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Coastal oceanographic conditions in the Prydz Bay region (East Antarctica) during the Holocene recorded in an isolation basin
Abstract
Information on East Antarctic coastal environments during the Holocene is relatively sparse. This is surprising as sedimentary records from the interface between land and sea can provide chronologies of climatic change, isostatic uplift, relative sea level and the colonization of newly formed biomes. Here we examine a sediment core from Pup Lagoon, a coastal lake in the Larsemann Hills, East Antarctica. Sediment stratigraphy, fossil pigments and diatoms were used to infer the sequence of Holocene environmental and climatic change. Results show that between 5800 and 5500 cal. yr BP the marine coast of Prydz Bay was characterized by stratified, open-water conditions during spring and summer and seasonally warm conditions. From 5500 to 2750 cal. yr BP sea-ice duration in Prydz Bay increased with the coast being ice-free for 2–3 months each year, conditions which are similar to the present day. A return to stratified, open-water conditions and a reduction in winter sea-ice extent between 2750 and 2200 cal. yr BP is signalled by enhanced biogenic production and more open-water diatom taxa. This is consistent with evidence for the mid-Holocene Hypsither mal detected in other records in East Antarctica. Isostatic isolation of the Pup Lagoon basin from the sea between 2200 and 2000 cal. yr BP slightly precedes the emergence of lakes with comparable sill heights from the nearby Vestfold Hills. The colonization of Pup Lagoon after its isolation as a freshwater lake was initiated by a siliceous flora dominated by stomatocysts with microbial mat development being prevented by mechanical or physical stress. A brief period of marine incursion following the mid-Holocene Hypsithermal may be related to local events such as iceberg calving or to minor sea-level change. Weighted averaging regression, used to infer salinity in the lacustrine zone, shows that from 1500 cal. yr BP Pup Lagoon is a freshwater lake, where the flora is dominated by stratified cyanobacterial mats, with green algae and diatoms as co-dominants, comparable to modern Pup Lagoon and other lakes in the Larsemann Hills.
... Table 3 Photosynthetic pigments in the Ok4C-1 sediment core from Lake Oyako-ike (pheo-b, pheophytin b; pyro-b, pyropheophorbide b; continued; μg/g). [10,15] ． Fucoxanthin および cis-diatoxanthin は緑藻類，珪藻およびシアノバクテリアの指標で あり， zeaxanthin は緑藻類およびシアノバクテリア の指標となるカロテノイドである [15,16] ．Lutein， [10,15,17] ． Cis-alloxanthin はクリプト藻に特徴的に含まれる カロテノイドである [18] ．Chlorobactene は，嫌気性 光合成バクテリアである緑色硫黄バクテリアの指 標である [19] ...
... Table 3 Photosynthetic pigments in the Ok4C-1 sediment core from Lake Oyako-ike (pheo-b, pheophytin b; pyro-b, pyropheophorbide b; continued; μg/g). [10,15] ． Fucoxanthin および cis-diatoxanthin は緑藻類，珪藻およびシアノバクテリアの指標で あり， zeaxanthin は緑藻類およびシアノバクテリア の指標となるカロテノイドである [15,16] ．Lutein， [10,15,17] ． Cis-alloxanthin はクリプト藻に特徴的に含まれる カロテノイドである [18] ．Chlorobactene は，嫌気性 光合成バクテリアである緑色硫黄バクテリアの指 標である [19] ...
... Table 3 Photosynthetic pigments in the Ok4C-1 sediment core from Lake Oyako-ike (pheo-b, pheophytin b; pyro-b, pyropheophorbide b; continued; μg/g). [10,15] ． Fucoxanthin および cis-diatoxanthin は緑藻類，珪藻およびシアノバクテリアの指標で あり， zeaxanthin は緑藻類およびシアノバクテリア の指標となるカロテノイドである [15,16] ．Lutein， [10,15,17] ． Cis-alloxanthin はクリプト藻に特徴的に含まれる カロテノイドである [18] ．Chlorobactene は，嫌気性 光合成バクテリアである緑色硫黄バクテリアの指 標である [19] ...
We studied Holocene paleoenvironmental changes in the Soya Kaigan of East Antarctica inferred from the analyses of Lake Oyako-ike sediment core (Ok4C-01, length 135 cm) , along with sedimentary facies and AMS ¹⁴C dating. The Ok4C-01 core was composed of clayish mud containing laminae between 135-65.5 cm. This was overlain by organic sediments containing algal mats between 65.5-0 cm. The mean sedimentation rate and uplifting rate were estimated to be 0.69 mm/y and 2.2 mm/y, respectively. The low biological production with diatom in coastal marine environments (135-74.75 cm, ca.2,170-1,300 cal BP), changes into green sulfur bacteria in stratified saline lake in 74.75-60.95 cm (ca.1,300-1,100 cal a BP), and then high biological production with cyanobacteria and green algae in lacustrine environments (60.95-0 cm, ca.1,100-220 cal BP). The ongoing retreat of glaciers and ongoing isostatic uplift during the mid-Holocene Hypsithermal (4.5-2.8 cal ka BP) and thereafter are the main reasons for this isolation, whereas eustatic sea level change is believed to have played only a minor role.
... Records of past microbial flora are archived in the stratigraphic sediment deposits in the bottom of the lakes. As one of only four major ice-free regions in East Antarctica, these stratigraphic sequences in the Larsemann Hills are being used as an important tool for understanding climate change, ice sheet extent, deglaciation history of the Antarctic coastline, and changes in the lacustrine and terrestrial environment (Squier et al. 2002;Verleyen et al. 2004aVerleyen et al. , 2004b. ...
... Identification of the diatom species was mainly based on Sabbe et al. (2003) and references therein. Communities from both cores were divided into zones following standard ordination and cluster analyses on the basis of total relative abundances of diatoms (Verleyen et al. 2004a(Verleyen et al. , 2004b. The surface area (m 2 ) of each diatom species was calculated with BIOVOL ver. ...
... (c) Water column and sea ice (TDB planktonic /TChla) and benthic (TDB benthic /TChla) diatom production relative to total primary production on the basis of absolute diatom counts, biovolume measurements, and proportion of benthic taxa. Zoning is based on diatom data and macroscopic lithological observations in the field (Verleyen et al. 2004a). entire core (r 2 ϭ 0.187, p Ͻ 0.0001; Table 4); however, correlations were highly significant in the marine intervals (r 2 ϭ 0.557, p Ͻ 0.0001) but not in the lacustrine core sections (r 2 ϭ 0.102, p ϭ 0.111; Table 4). ...
Reconstructions of historical primary production, and of the algal groups and habitats that contribute to it, are fundamental in studies of climate and environmental change in both marine and freshwater environments. The aims of this study were to critically evaluate morphological and biogeochemical markers of diatom production by direct comparison of diatom marker pigments with absolute diatom biovolume and to partition diatom production between the main habitats (plankton, sea ice, and benthos). Sediments in two cores from the Larsemann Hills, Antarctica, spanning the last 10,000 yr, were analyzed for siliceous microfossils by microscopy and for fossil pigments by high-performance liquid chromatography. Diatom pigments (diadinoxanthin, diatoxanthin, fucoxanthin) were highly correlated ( $r^{2}=0.557$ and 0.358, p < 0.0001) with diatom biovolume in the marine intervals of both cores, but only weakly correlated in the lacustrine sections ( $\text{r}^{2}=0.102$ , p = 0.111; $\text{r}^{2}=0.223$ , p = 0.001, after correction for temporal autocorrelation), possibly because of frustule dissolution and selective degradation of diadinoxanthin and diatoxanthin. In contrast, fucoxanthin was better preserved. By combining both microfossil and pigment proxies, we obtained a first estimate of diatom production in specific habitats (benthic and planktonic). Benthic diatom production was greatest in the lacustrine core sections, when benthic microbial mats dominated the flora, whereas diatoms were associated mainly with the water column and sea ice during the marine intervals. The combination of both proxies in marine and freshwater environments permits more accurate interpretation of pigment and diatom data in paleo- and neoecological research and the partitioning of diatom production between habitats.
... Records of past microbial flora are archived in the stratigraphic sediment deposits in the bottom of the lakes. As one of only four major ice-free regions in East Antarctica, these stratigraphic sequences in the Larsemann Hills are being used as an important tool for understanding climate change, ice sheet extent, deglaciation history of the Antarctic coastline, and changes in the lacustrine and terrestrial environment (Squier et al. 2002;Verleyen et al. 2004aVerleyen et al. , 2004b. ...
... Identification of the diatom species was mainly based on Sabbe et al. (2003) and references therein. Communities from both cores were divided into zones following standard ordination and cluster analyses on the basis of total relative abundances of diatoms (Verleyen et al. 2004a(Verleyen et al. , 2004b. The surface area (m 2 ) of each diatom species was calculated with BIOVOL ver. ...
... (c) Water column and sea ice (TDB planktonic /TChla) and benthic (TDB benthic /TChla) diatom production relative to total primary production on the basis of absolute diatom counts, biovolume measurements, and proportion of benthic taxa. Zoning is based on diatom data and macroscopic lithological observations in the field (Verleyen et al. 2004a). entire core (r 2 ϭ 0.187, p Ͻ 0.0001; Table 4); however, correlations were highly significant in the marine intervals (r 2 ϭ 0.557, p Ͻ 0.0001) but not in the lacustrine core sections (r 2 ϭ 0.102, p ϭ 0.111; Table 4). ...
Reconstructions of historical primary production, and of the algal groups and habitats that contribute to it, are fundamental in studies of climate and environmental change in both marine and freshwater environments. The aims of this study were to critically evaluate morphological and biogeochemical markers of diatom production by direct comparison of diatom marker pigments with absolute diatom biovolume and to partition diatom production between the main habitats (plankton, sea ice, and benthos). Sediments in two cores from the Larsemann Hills, Antarctica, spanning the last 10,000 yr, were analyzed for siliceous microfossils by microscopy and for fossil pigments by high-performance liquid chromatography. Diatom pigments (diadinoxanthin, diatoxanthin, fucoxanthin) were highly correlated (r 2 5 0.557 and 0.358, p , 0.0001) with diatom biovolume in the marine intervals of both cores, but only weakly correlated in the lacustrine sections (r 2 5 0.102, p 5 0.111; r 2 5 0.223, p 5 0.001, after correction for temporal autocorrelation), possibly because of frustule dissolution and selective degradation of diadinoxanthin and diatoxanthin. In contrast, fucoxanthin was better preserved. By combining both microfossil and pigment proxies, we obtained a first estimate of diatom production in specific habitats (benthic and planktonic). Benthic diatom production was greatest in the lacustrine core sections, when benthic microbial mats dominated the flora, whereas diatoms were associated mainly with the water column and sea ice during the marine intervals. The combination of both proxies in marine and freshwater environments permits more accurate interpretation of pigment and diatom data in paleo- and neoecological research and the partitioning of diatom production between habitats.
... Pup Lagoon (76 ° 03¢ E-69 ° 25¢ S) is a shallow lake, which became isolated from the sea at c. 2002-2307 cal yr BP (2150 ± 45 14 C yr BP) due to regional isostatic processes ( Verleyen et al. 2004a). The lake is located c. 100 m from the coast of Stornes and c. 2250 m from the continental ice sheet. ...
... The core was photographed, macroscopically described, sectioned into 1 cm slices in the field and frozen at below À20 °C until analysis. The upper 120 cm of this core, which fall within the lacustrine sediment sequence ( Verleyen et al. 2004a), was analysed in the present study. Figure 2. Non-linear regression linking modern TScyt/TCC mod content to lake depth, based on 28 lakes from the Larsemann Hills ( Hodgson et al. 2004). ...
... Linear age depth models were applied to the minimum and maximum calibrated 14 C dates from the Pup Lagoon core in order to interpolate the ages of major changes in the sediment proxies (Table 1, Figure 3). Lacustrine sediments in the Pup Lagoon core, deposited after isostatic uplift and subsequent isolation of the basin from the sea, are dominated by freshwater diatoms (e.g., Stauroforma inermis and Pinnularia microstauron) and consist of laminated undisturbed microbial mats ( Verleyen et al. 2004a). Inferred lake depth and salinity, both known to influence scytonemin production ( Dillon et al. 2002;Hodgson et al. 2004), were variable during the first $450390 years of the lacustrine phase ( Verleyen et al. 2004a). ...
Late Holocene changes in the ultraviolet radiation (UVR) penetration in a lake in the Larsemann Hills (East Antarctica) were reconstructed using sediment core proxies based on fossil pigments (scytonemins and its derivatives) and siliceous microfossils. The influence of changes in lake depth on the UVR proxy was excluded by applying a correction, based on the non-linear relation between modern scytonemin concentrations and lake depth in a regional reference data set, and the record of past lake depths inferred using a diatom based transfer function in the sediment core. Results showed four well-defined maxima in the UVR proxy during the last 1600–1800years, centred around 1820–1780, 1580–1490, 790–580 and 680–440 AD. Several mechanisms may account for these observed changes in UVR penetration, including past variability in cloud cover, atmospheric turbidity, ozone column depth, snow cover on the lake ice, DOM concentrations and lake-ice thickness and transparency resulting from temperature fluctuations. Although some gaps remain in our knowledge of scytonemin production in relation to the limnology of Antarctic lakes, the results highlight the importance and potential of the sediments in these highly transparent water bodies as archives of changes in past UVR receipt at the Earth’s surface.
... Stanols are found in microalgae (dinoflagellates, diatoms and raphidphytes, Volkman et al. 1998) and are also formed by bacterial reduction of stenols Fig. 7 Depth profiles of photosynthetic pigments in the Sk4C-02 sediment core from Lake Skallen Oike. Chlorophyll a, pheophythin a and pyrophyophytin a: ubiquitous (Verleyen et al. 2004b;Tani et al. 2009). Fucoxanthin and cisdiatoxanthin: Diatoms, Dinophyta, Chrysophyta, brown algae and Heptophycae (Chihara 1997;Verleyen et al. 2004b). ...
... Chlorophyll a, pheophythin a and pyrophyophytin a: ubiquitous (Verleyen et al. 2004b;Tani et al. 2009). Fucoxanthin and cisdiatoxanthin: Diatoms, Dinophyta, Chrysophyta, brown algae and Heptophycae (Chihara 1997;Verleyen et al. 2004b). Zeaxanthin: Cyanobacteria, Chlorophyta and mosses (Verleyen et al. 2004b;Hodgson et al. 2006). ...
... Fucoxanthin and cisdiatoxanthin: Diatoms, Dinophyta, Chrysophyta, brown algae and Heptophycae (Chihara 1997;Verleyen et al. 2004b). Zeaxanthin: Cyanobacteria, Chlorophyta and mosses (Verleyen et al. 2004b;Hodgson et al. 2006). Lutein: Chlorophyta, red algae, Charophyceae and vascular plants (Chihara 1997;Verlayen et al. 2004b;Tani et al. 2009). ...
Antarctic climate changes influence environmental changes at both regional and local scales. Here we report Holocene paleolimnological
changes in lake sediment core Sk4C-02 (length 378.0cm) from Lake Skallen Oike in the Soya Kaigan region of East Antarctica
inferred from analyses of sedimentary facies, a range of organic components, isotope ratios of organic carbon and nitrogen,
and carbon-14 dating by Tandetron accelerator mass spectrometry. The sediment core was composed of clayish mud (378.0–152.5cm)
overlain by organic sediments (152.5cm-surface). The age of the surface and the core bottom were 150 (AD1950-1640) and ca.
7,030±73 calibrated years before present (cal BP), respectively, and the mean sedimentation rate was estimated to be 0.55mm/year.
Multi-proxy analyses revealed that the principal environmental change in the core is a transition from marine to lacustrine
environments which occurred at a depth of 152.5cm (ca. 3,590cal BP). This was caused by relative sea level change brought
about by ongoing retreat of glaciers during the mid-Holocene warming of Antarctica, and ongoing isostatic uplift which outpaced
changes in global (eustatic) sea level. The mean isostatic uplift rate was calculated to be 2.8mm/year. The coastal marine
period (378.0–152.5cm, ca. 7,030–3,590cal BP) was characterized by low biological production with the predominance of diatoms.
During the transition period from marine to freshwater conditions (152.5-approximately 135cm, ca. 3,590–3,290cal BP) the
lake was stratified with marine water overlain by freshwater, with a chemocline and an anoxic (sulfidic) layer in the bottom
of the photic zone. Green sulfur bacteria and Cryptophyta were the major photosynthetic organisms. The Cryptophyta appeared
to be tolerant of the moderate salinity and stratified water conditions. The lacustrine period (approximately 135cm-surface,
ca. 3,290cal BP-present) was characterized by high biological production by green algae (e.g. Comarium clepsydra and Oedegonium spp.) with some contributions from cyanobacteria and diatoms. Biological production during this period was 8.7 times higher
than during the coastal marine period.
KeywordsAntarctic lake-Paleolimnological change-Sediment core-Organic components-AMS carbon-14 dating-Uplifting rate
... Zones KPI and KP II were dated at 150, 155 and 156 cm sediment depth by Accelerator Mass Spectrometry radiocarbon analysis at Beta Analytic, Florida. These supplemented the existing chronological control for the core which consisted of 8 radiocarbon dates and 2 TL dates (Hodgson et al., 2001; Verleyen et al., 2004a). Calibration of conventional radiocarbon ages to calendar years was undertaken using the calibration data set CalPal-2007Hulu (Weninger and Jö ris, 2008) using CalPal-2007online (Danzeglocke et al., 2008). ...
... Calibration of conventional radiocarbon ages to calendar years was undertaken using the calibration data set CalPal-2007Hulu (Weninger and Jö ris, 2008) using CalPal-2007online (Danzeglocke et al., 2008). To determine sediment provenance (marine or freshwater), diatoms were counted at high resolution using the methods described in Verleyen et al. (2004a Verleyen et al. ( , 2005). Pigments (chlorophylls, bacteriochlorophylls and carotenoids) were analysed using high performance liquid chromatography–mass spectrometry (HPLC– MS) following methods described in Airs et al. (2001) in concentrated acetone extracts of samples at 150–151, 154–155, 155–156 and 156–157 cm and compared with the pigment content of freshwater sediments in zone KPIII (sample 135–136 cm) and previously published pigment analyses of both freshwater and marine sediments in the remainder of the core (Squier et al., 2002). ...
... Samples from 158 to 156 cm are dominated by a marine flora consisting of Tryblionella marginulata, Thalassiosira oestrupii and Fragilariopsis curta. T. marginulata is characteristic of early stages of transition between marine and lacustrine conditions (contacts) and is found abundantly in a later Holocene marine to freshwater transition zone in this core (Verleyen et al., 2004bVerleyen et al., , 2005), and in a core from nearby Pup Lagoon (Verleyen et al., 2004a). The marine diatom flora includes one taxon T. oestroepii that is present in earlier Pliocene deposits in the Larsemann Hills (McMinn and Harwood, 1995) and the Vestfold Hills some 120 km distant (Harwood et al., 2000; Whitehead et al., 2001) and F. curta which is found in the Pliocene Sørsdal Formation of the Vestfold Hills but not in the Larsemann Hills (Harwood et al., 2000). ...
In this paper we present geological evidence from the Larsemann Hills (Lambert Glacier – Amery Ice Shelf region, East Antarctica) of marine sediments at an altitude of c. 8 m a.s.l., as revealed by diatom, pigment and geochemical proxies in a lake sediment core. The sediments yielded radiocarbon dates between c. 26 650 and 28 750 14C yr BP (31 366–33 228 cal yr BP). This information can be used to constrain relative sea level adjacent to the Lambert Glacier at the end of Marine Isotope Stage 3. These data are compared with the age and altitude of Marine Isotope Stage 3 marine deposits elsewhere in East Antarctica and discussed with reference to late Quaternary ice sheet history and eustatic sea-level change.
... With the onset of Holocene warming ∼11.5 ka BP, the glaciers may have retreated, giving way to five large proglacial lakes occupying the low lying valleys of SO (Fig. 8. B). This is similar to Larsemann Hills where between 11.5 and 9.5 ka BP the lakes became ice free and an early Holocene optimum has been inferred (Verleyen et al., 2003(Verleyen et al., , 2004a(Verleyen et al., , 2004bHodgson et al., 2004). This warming also coincides with the beginning of the Holocene deglaciation of other East Antarctic oases (Ingόlfsson et al., 1998;Gore et al., 2001;Hodgson et al., 2001;Kirkup et al., 2002). ...
... With the onset of Holocene warming ∼11.5 ka BP, the glaciers may have retreated, giving way to five large proglacial lakes occupying the low lying valleys of SO (Fig. 8. B). This is similar to Larsemann Hills where between 11.5 and 9.5 ka BP the lakes became ice free and an early Holocene optimum has been inferred (Verleyen et al., 2003(Verleyen et al., , 2004a(Verleyen et al., , 2004bHodgson et al., 2004). This warming also coincides with the beginning of the Holocene deglaciation of other East Antarctic oases (Ingόlfsson et al., 1998;Gore et al., 2001;Hodgson et al., 2001;Kirkup et al., 2002). ...
... The mud cracks indicate that the lake had recently dried as it has black, wet sediment indicative of recent water influence. The salt deposits on their surfaces (Fig. 2 H) today may be linked with a slightly negative moisture balance during the neoglacial cooling that commenced at ca. 2460 to 1800 BP and is continuing to the present (Taylor et al., 2001;Brachfeld et al., 2002;Taylor and McMinn, 2002;Cremer et al., 2003and Verleyen et al., 2004a, 2004b. Soil formation in the oasis is negligible, but thin (mm to cm scale) dark clay organic layers are encountered in many of the sections although the LOI shows a range (2e8%) however variation in the pattern is noticed. ...
Large former glacial lakes and their sediments are described from the Schirmacher Oasis region of East Antarctica. The water bodies were present during the Late Quaternary (∼10–3 ka BP) and have reduced in size by negative water balance. This desiccation can possibly be attributed to the combined effect of recession of glaciers feeding them, low melt water, low precipitation and strong winds. Seven representative sections from five dry lake beds have been studied using loss-on-ignition (LOI) and Magnetic Susceptibility (MS). The LOI indicates a very low organic content, while MS enables assumptions to be made about the reconstruction of changing detrital input. Detailed study of sediment profiles was used to reconstruct the evolution of the Schirmacher Oasis from 13 ka BP to the present. These lacustrine sediments are a very important source of information on the Quaternary geological history of the Schirmacher Oasis.
... In short, lacustrine diatoms are generally used in combination with transfer functions to enable the quantitative reconstruction of past changes in the moisture balance (e.g., Roberts and McMinn, 1998; Verleyen et al., 2003) and/or nutrient levels (Roberts et al., 2004). Marine diatoms are divided into sea-ice related and open water taxa (e.g., Verleyen et al., 2004a) based upon their presence in modern analogue assemblages of the Southern Ocean (e.g., Armand et al., 2005; Crosta et al., 2005). Faunal microfossils are used to study past changes in lake ecology (Cromer et al., 2005Cromer et al., , 2006). ...
... Faunal microfossils are used to study past changes in lake ecology (Cromer et al., 2005Cromer et al., , 2006). Fossil pigments enable the reconstruction of changes in the marine and lacustrine autotrophic communities, primary productivity, and changes in ice cover dynamics (e.g., Hodgson et al., 2003; Verleyen et al., 2004a Verleyen et al., , 2005). Sedimentological and geochemical proxies are used to reconstruct transitions between different sedimentary environments (e.g., glacial vs. lacustrine), primary productivity [e.g., loss-on-ignition, total organic carbon content (TOC)], whether a reduction or oxidation occurs in the water column through reduced or increased ice cover [total sulphur content (TS) e.g., Wagner et al., 2006], or the presence of vegetation in the catchment area (the total carbon vs. total nitrogen content (TC/TN), Wagner et al., 2006). ...
... In the Larsemann Hills this warm period is dated between c. 4 and 2 ka BP (Fig.3). There, relatively wet conditions resulted in increased lake water levels, which predate then overlap with the coastal marine optimum inferred from the presence of open water marine diatoms in isolation basins at 2.7 to 2.2 ka BP (Verleyen et al., 2004aVerleyen et al., , 2004b). A short return to dry conditions and low water levels is present in one of the lake records at c. 3.2 ka BP (Verleyen et al., 2004b). ...
We review the post-glacial climate variability along the East Antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere. Nearly all East Antarctic records show a near-synchronous Early Holocene climate optimum (11.5–9 ka BP), coinciding with the deglaciation of currently ice-free regions and the optimum recorded in Antarctic ice and marine sediment cores. Shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the Early Holocene warm period, and show complex regional patterns, but an overall trend of cooling in the terrestrial records. A Mid to Late Holocene warm period is present in many East Antarctic lake and shallow coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4.7 and 1 ka BP, which overlaps with a similar optimum found in Antarctic Peninsula terrestrial records. The differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify. Nearly all records show a neoglacial cooling from 2 ka BP onwards. There is no evidence along the East Antarctic coastline for an equivalent to the Northern Hemisphere Medieval Warm Period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the Northern Hemisphere's Little Ice Age. There is a need for well-dated, high resolution climate records in coastal East Antarctica and particularly in Terre Adélie, Dronning Maud Land and Enderby Land to fully understand the regional climate anomalies, the disparity between marine and terrestrial records, and to determine the significance of the heterogeneous temperature trends being measured in the Antarctic today.
... It was soon recognised that the sediments of many lakes, particularly the abundant meromictic (permanently stratified) lakes, provided superb records of wellpreserved microfossils, notably diatoms, which could be used indirectly as indicators of palaeo-climate change (e.g., Bronge, 1992;Björck et al., 1996;Roberts et al., , 2001. Recently, more attention has been given directly to the palaeoecology of Antarctic lakes (e.g., Squier et al., 2002;Verleyen et al., 2004). In many cases, these studies still focus on secondary proxies, in that they examine chemical or genetic signatures of a particular class of organism (e.g. ...
... We use these data, along with previously-published sediment records, to describe changes in the lake's ecology. The changes in the ecology recorded in the sediments of Ace Lake provide a model for the ecological development of similar marine-derived saline lakes that occur both elsewhere in the Vestfold Hills (Pickard et al., 1986;Gibson, 1999) and in other regions of Antarctica (Tominaga and Fukui, 1981;Roberts et al., 2004;Verleyen et al., 2004). ...
The sediment record of the fauna of Ace Lake, a saline meromictic lake in the Vestfold Hills, Antarctica, consists of copepod eggs, spermatophores and exoskeletal fragments, rotifer and tintinnid loricae, and foraminiferal and folliculinid tests. The relative abundance of these remains, along with other characteristics of the core, allows the development of a coherent picture of the progress of Ace Lake from a species-poor, freshwater lake early in the Holocene to a biodiverse marine basin following a marine transgression. Subsequent sea level fall reformed Ace Lake as a saline lake and productivity initially increased after isolation. After a major event, possibly associated with overturn of the meromictic lake, biodiversity and productivity decreased, and have continued to do so until the present.
... Izaguirre et al. (2003) studied the planktonic communities (zooplankton, phytoplankton, bacterioplankton) and their main limnological features to describe the relative contributions of autotrophic and heterotrophic components of their food webs in Hope Bay. Verleyen et al. (2004) studied diatoms, chrysophytes and silicoflagellates in sediment cores from three lakes in Larsemann Hills to show that the western peninsula, Stornes, and offshore islands were covered by ice between 30,000 years BP and 13,500 years BP in Larsemann Hills. Cromer et al. (2005) Neloy Khare et al studied copepod eggs, spermatophores and exoskeletal fragments, rotifer and tintinnid loricae, and foraminiferal and folliculinid tests to develop a coherent picture of the progress of Ace Lake. ...
... Verleyen et al. (2003) stated that salinity is the most important environmental variable explaining the variance in the diatom flora on the basis of the data of diatoms and water chemistry from Larsemann Hills, the Bolingen Islands, the Vestfold Hills, the Rauer Islands and the Windmill Islands. Verleyen et al. (2004) analyzed sediment stratigraphy, fossil pigments and diatoms in a sediment core recovered from Pup Lagoon, a coastal lake in the Larsemann Hills to infer the sequence of Holocene environmental and climatic change. Hall et al. (2006) studied geomorphology, sedimentology and importance of reconstructing the glacial history of the Dry Valleys using lake-ice conveyor deposits. ...
Bilogical composition and biodiversity alongwith microbial study became very upcoming subjects in present science. In recent time the lakes of Antarctica are the main area for biological studies. To understand the ecology and climate, and hence the evolution of Antarctica, different aspects of biological studies have been carried out in Antarctic Lake waterbodies. The biotic compositional changes through time in lake water reflect the climatic changes of the lake sites as well as evolutionary and migratory path of such biological community. Here the review of some important studies on biology in Antarctic lake area is provided in details. Along with this the geomorphological studies of Antarctic lakes along with their evolution is also discussed to understand the interlink between lake structure and its biological composition through time.
... A variety of macroscopically different mat morphologies have been recognised and their distribution has been related to a suite of environmental factors, including depth, sedimentation of inorganic sediment, light, concentrations of dissolved gases and alkalinity of the lake water (Wharton, Parker & Simmons, 1983; Squyres et al., 1991; EllisEvans, 1996;). Perennial microbial mats forming deposits several metres thick are widespread in lakes of the Larsemann Hills and Bølingen Islands, two important icefree oases in continental East-Antarctica (Hodgson et al., 2001a; Verleyen et al., 2003 Verleyen et al., , 2004). Minimal bioturbation (due to the absence of larger metazoa), limited wind-induced hydrodynamic mixing (most lakes are covered by ice for more than 10 months per year) and slow decomposition are thought to contribute to the strongly laminated, well-preserved nature of these deposits in the deeper lakes (>5 m). ...
... We examine the nature of their relationships with mat physiognomy, environmental conditions and geomorphological data using multivariate ordination techniques. This study is part of a broader programme on the biodiversity of microbial communities in continental Antarctic lakes and forms the framework for the development of biological proxies based on diatoms, pigment composition and genetic fingerprinting of fossil cyanobacterial assemblages (Squier, Hodgson & Keely, 2002; Verleyen et al., 2003 Verleyen et al., , 2004; A. Taton et al., unpublished data). ...
1. Lakes and ponds in the Larsemann Hills and Bølingen Islands (East‐Antarctica) were characterised by cyanobacteria‐dominated, benthic microbial mats. A 56‐lake dataset representing the limnological diversity among the more than 150 lakes and ponds in the region was developed to identify and quantify the abiotic conditions associated with cyanobacterial and diatom communities.
2. Limnological diversity in the lakes of the Larsemann Hills and Bølingen Islands was associated primarily with conductivity and conductivity‐related variables (concentrations of major ions and alkalinity), and variation in lake morphometry (depth, catchment and lake area). Low concentrations of pigments, phosphate, nitrogen, DOC and TOC in the water column of most lakes suggest extremely low water column productivity and hence high water clarity, and may thus contribute to the ecological success of benthic microbial mats in this region.
3. Benthic communities consisted of prostrate and sometimes finely laminated mats, flake mats, epilithic and interstitial microbial mats. Mat physiognomy and carotenoid/chlorophyll ratios were strongly related to lake depth, but not to conductivity.
4. Morphological‐taxonomic analyses revealed the presence of 26 diatom morphospecies and 33 cyanobacterial morphotypes. Mats of shallow lakes (interstitial and flake mats) and those of deeper lakes (prostrate mats) were characterised by different dominant cyanobacterial morphotypes. No relationship was found between the distribution of these morphotypes and conductivity. In contrast, variation in diatom species composition was strongly related to both lake depth and conductivity. Shallow ponds were mainly characterised by aerial diatoms (e.g. Diadesmis cf. perpusilla and Hantzschia spp.). In deep lakes, communities were dominated by Psammothidium abundans and Stauroforma inermis . Lakes with conductivities higher than ±1.5 mS cm ⁻¹ became susceptible to freezing out of salts and hence pronounced conductivity fluctuations. In these lakes P. abundans and S. inermis were replaced by Amphora veneta . Stomatocysts were important only in shallow freshwater lakes.
5. Ice cover influenced microbial mat structure and composition both directly by physical disturbance in shallow lakes and by influencing light availability in deeper lakes, as well as indirectly by generating conductivity increases and promoting the development of seasonal anoxia.
6. The relationships between diatom species composition and conductivity, and diatom species composition and depth, were statistically significant. Transfer functions based on these data can therefore be used in paleolimnological reconstruction to infer changes in the precipitation–evaporation balance in continental Antarctic lakes.
... The gradual increase in temperature recorded in Antarctic ice cores is interrupted by a short cooling period, the Antarctic Cold Reversal (ACR; , that coincides with a rapid rise in global sea level (MWP1A; Clark et al., 2002), suggested to be a trigger for the Bølling-Allerød warm period (14,600 14 C yr B.P.) in the North (Weaver et al., 2003), detected in ice cores from Greenland and terrestrial records in the Northern Hemisphere (Benson et al., 1997). In Antarctica, temperatures increased immediately after the ACR, leading to deglaciation of the currently ice-free coastal oases (e.g., Ingó lfsson et al., 1998;Roberts and McMinn, 1999;Verleyen et al., 2004a). In the Lake Reid core however, lake water level remains quasiconstant, implying little variation in the moisture balance (and thus precipitation-evaporation balance and meltwater regime) during Termination I, the ACR and the Younger Dryas cold event (ca. ...
... The only evidence of hydrological changes at this time is a steady depletion of y 18 O down to À12°by 43 cm, possibly reflecting the onset of deglaciation and the renewed input of depleted meltwater from catchment snow banks. Together these data imply that the terrestrial environment in this part of East Antarctica responded to slowly changing temperatures after Termination I, possibly due to the buffering effect of ice sheets that remained grounded on some parts of the continental shelf of Prydz Bay before 14,000 cal yr B.P. (Domack et al., 1998;Verleyen et al., 2004a) and the presence of firnified snow and ice in the Broknes valleys. This is in contrast to present-day lakes in the maritime Antarctic, which have been shown to amplify climate changes during deglaciation through increases in their effective catchment areas leading to higher inputs of nutrients (Quayle et al., 2002). ...
Little is known about the response of terrestrial East Antarctica to climate changes during the last glacial–interglacial cycle. Here we present a continuous sediment record from a lake in the Larsemann Hills, situated on a peninsula believed to have been ice-free for at least 40,000 yr. A mutli-proxy data set including geochronology, diatoms, pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record. We interpret this as Marine Isotope Stage 5e after application of a chronological age-depth model and similar ice core evidence. Dry and cold conditions are inferred during the last glacial, with lake-level minima, floristic changes towards a shallow water algal community, and a greater biological receipt of ultraviolet radiation. During the Last Glacial Maximum and Termination I the lake was perennially ice-covered, with minimal snowmelt in the catchment. After ca. 10,500 cal yr B.P., the lake became seasonally moated or ice-free during summer. Despite a low accumulation rate, the sediments document some Holocene environmental changes including neoglacial cooling after ca. 2450 cal yr B.P., and a gradual increase in aridity and salinity to the present.
... The isolation-basins approach is widely used in reconstructions of shoreline displacement resulting from neotectonic, isostatic or eustatic processes all over the world (Corner et al., 1999;Donner et al., 1977;Davydova, 1984;García-Rodríguez et al., 2001;Lie et al., 1983;Long et al., 2011;Miettinen et al., 2007;Roe et al., 2009;Sangren et al., 2004;Shennan et al., 2000;Smith et al., 2005;Snyder et al., 1997;Verleyen et al., 2004;Yu et al., 2004). ...
This paper discusses the results of siliceous microfossils studies performed in a “staircase” of four isolation basins (33.7 m–2.9 m a.s.l.) on Big Solovetskiy Island (Solovki Archipelago, the White Sea). Diatoms were used as a primary group for paleoinferences, while chrysophyte cysts and sponge spicules also demonstrated high indicative potential. In all study lakes, the siliceous microfossils stratigraphy revealed three main stages of their evolution, i.e. large-basin, transitional and small-lake stages, each characterized by certain composition of the diatom assemblages and floristic diversity, relative abundances of chrysophyte cysts and sponge spicules, and siliceous microfossils concentrations. In the uppermost lake, glaciolacustrine environments unfavorable for aquatic biota existed during the large-basin stage. The proglacial lake stage terminated prior to ca. 10.4 cal ka BP, followed by a (semi)terrestrial episode before the transition to small-lake environments. In the other three lakes, marine environments were inferred at the earlier stage, characterized by the predominance of marine and brackish-marine diatoms, increased proportions of sponge spicules and low “cysts to diatoms” ratio. At the transitional marine-freshwater stage, mass growth of small fragilarioid diatoms and decreased abundances of spicules indicated unstable environments, while increased proportions of cysts pointed to progressive freshening of the basins. The duration of the marine-freshwater transition expectedly prolonged from ca. 200 yr in the upper basin (16.6 m a.s.l) to ca. 500 yr in the lowermost lake (2.9 m a.s.l.). The isolation from the sea took place between ca. 6.3 and 1.4 cal ka BP. At the small-lake stage, siliceous microfossils stratigraphies reflected local specifics of the basins and their catchments. We argue that besides traditionally used diatom data, relative and absolute abundances of siliceous microfossils also possess high indicative value for isolation basin studies. Our study demonstrated that marine waters on Big Solovetskiy Island never reached ca. 34 m a.s.l. during the Holocene, unlike the western coast of the Onega Bay where the Preboreal marine intrusion was recorded even at higher elevated localities. Different rates and amplitudes of shoreline displacement are thus suggested for the inner and outer parts of the Onega Bay. During the mid-Holocene Tapes transgression, before ca. 6.3 cal ka BP, the relative sea level on Big Solovetskiy Island exceeded 17 m a.s.l. The average estimated rates of the shoreline retreat during the second half of the Holocene gradually decreased from 0.28 cm year⁻¹ to 0.2 cm year⁻¹, indicating slowed isostatic uplift.
... During such periods, the salinity of the aquatic bodies increases, leading to the prolific growth of marginal marine flora and fauna, like foraminifera and diatoms. The lakes in the marginal regions of Antarctica, provide ample opportunity to reconstruct regional climatic changes (Roberts and McMinn, 1999;Roberts et al., 2000;Hodgson et al., 2001;Verleyen et al., 2004;Gibson et al., 2006), including changes in the ice-sheet extent and sea-level (Gillieson, 1991;Burgess et al., 1994;Zwartz et al., 1998). The past climate records as inferred from the lake sediments match well with the ice-core records, thus indicating the robustness of lake sediment based proxies and paleoclimatic records (Roberts et al., 2001). ...
The faunal (foraminiferal and diatom abundance) and sedimentological analysis was carried out on two cores collected from a coastal lake in the Vestfold Hills region of Antarctica. Out of a couple of cores collected from the same lake, the one closer to the marine inlet, contained abundant foraminifera and the diatoms were dominant in the second core. The radiocarbon dating of the organic matter revealed that the sediments were inverted, with two sequences of younger sediments overlain by older sediments. The increased abundance of marine microfossils, including both the foraminifera and diatoms in inverted layers, suggests that the sediments were transported from the adjacent shelf. The transport from the shelf is further confirmed by the abundant presence of planktic foraminiferal shells in the sediments. The planktic foraminifera are relatively deeper dwellers and thus confirm the transport of material from relatively deeper water depths. The transport of older marine sediments from the nearby shelf, into the lake against gravity is inferred as a result of storm/cyclone. Two such past storm-cyclone events are inferred as the core includes two sets of inverted sediments. The study suggests that faunal and sedimentological analysis in conjunction with chronology can be applied to infer past instances of extreme events in the high latitude regions.
... The start of biogenic sedimentation in the lacustrine sediments of glacial lakes and marine sedimentation in isolation basins provides minimum ages of initial ice sheet retreat over the terrestrial and nearshore marine environment respectively (cf. Hodgson et al., 2001;Verleyen et al., 2004; Table S1). The latter were combined with 14 C dates of marine fossils in raised beaches . ...
Abstract The East Antarctic Ice Sheet has relatively few field data to constrain its past volume and contribution to global sea-level change since the Last Glacial Maximum. We provide new data on deglaciation history and develop new relative sea-level (RSL) curves along an 80 km transect (from Skallen to Skarsvnes, Langhovde and the Ongul Islands) in Lützow Holm Bay, East Antarctica. The geological constraints were compared with output from two Glacial Isostatic Adjustment (GIA) models. The minimum radiocarbon age for regional deglaciation is c. 11,240 cal. yr BP on West Ongul Island with progressively younger deglaciation ages approaching the main regional ice outflow at Shirase Glacier. Marked regional differences in the magnitude and timing of RSL change were observed. More in particular, in Skarvsnes a minimum marine limit of 32.7 m was inferred, which is c. 12.7 m higher than previously published evidence, and at least 15 m higher than that reported in the other three ice-free areas. Current GIA model predictions slightly underestimate the rate of Late Holocene RSL fall at Skallen, Langhovde, and West Ongul, but provide a reasonable fit to the reconstructed minimum marine limit at these sites. GIA model predictions are unable to provide an explanation for the shape of the reconstructed RSL curve at Skarvsnes. We consider a range of possible explanations for the Skarvsnes RSL data and favour an interpretation where the anomalously high marine limit and rate of RSL fall is due to reactivation of a local fault.
... A previous study has also revealed that the Schirmacher Oasis was probably deglaciated at the Pleistocene-Holocene boundary (Gingele et al. 1997). This phenomenon is almost similar to that in the Larsemann Hills where the lakes were ice-free during 11.5 and 9.5 ka BP (Verleyen et al. 2003(Verleyen et al. , 2004a(Verleyen et al. , 2004bHodgson et al. 2004). This rise in temperature can be correlated with the commencement of the Holocene warming in other East Antarctic oases (Ingόlfsson et al. 1998;Gore et al. 2001;Hodgson et al. 2001;Kirkup et al. 2002). ...
Eighteen sediment samples from a 36 cm long sediment core retrieved from a proglacial lake (namely P 11) situated in the Schirmacher Oasis, East Antarctica, were analysed for the study of quartz grain morphology and microtexture, along with sand percentage, to reconstruct the paleoenvironmental changes in the lake during the Holocene. The age of the core ranges from 3.3 ka BP to 13.9 ka BP. The quartz grain morphology and microtexture reveal significant evidences of glacial transport along with some eolian and aqueous activities. On the basis of predominance of these signatures and the zonation from CONISS Cluster Analysis on the percentages of characteristic grain morphology and microtextures, the entire core has been subdivided into three major zones. From the paleoenvironmental perspective, it can be concluded that there is an onset of interglacial period at the advent of Holocene (12.3 ka BP), which reigned until 5.3 ka BP and thereafter, again a glacial environment prevailed until 3.3 ka BP with some variations in-between. The results indicate probable alternative colder and less colder phases in the study area, which are also well supported by the respective sand percentages in the sediments.
... The Amery Ice Shelf (Fig. 1) is one of the main sources of ice loss along the East Antarctic coastline, discharging ice from the Lambert Glacier and other glaciers into Prydz Bay. As a result there have been several studies of RSL changes at ice-free areas in this region including the Vestfold Hills (Zwartz et al., 1998), Larsemann Hills (Hodgson et al., 2009;Verleyen et al., 2005;Verleyen et al., 2004a) and Rauer Islands (Berg et al., 2010). This network of sites potentially enables an evaluation of local versus regional changes in ice volume and a robust assessment of regional ice mass change through the Holocene. ...
Prydz Bay is one of the largest embayments on the East Antarctic coast and it is the discharge point for approximately 16 % of the East Antarctic Ice Sheet. Geological constraints on the regional ice sheet history include evidence of past relative sea-level change at three sites; the Vestfold Hills, Rauer Islands and Larsemann Hills. In this paper we compile updated regional relative sea-level data from these sites. We compare these with a suite of relative sea-level predictions derived from glacial isostatic adjustment models and discuss the significance of departures between the models and the field evidence. The compiled geological data extend the relative sea-level curve for this region to 11258 cal yr BP and include new constraints based on abandoned penguin colonies, new isolation basin data in the Vestfold Hills, validation of a submarine relative sea-level constraint in the Rauer Islands and recalibrated radiocarbon ages at all sites dating from 12728 cal yr BP. The field data show rapid increases in rates of relative sea level rise of 12-48 mm/yr between 10473 (or 9678) and 9411 cal yr BP in the Vestfold Hills and of 8.8 mm/yr between 8882 and 8563 cal yr BP in the Larsemann Hills. The relative sea-level high stands of ≥ 8.8 m from 9411 to after 7564 cal yr BP (Vestfold Hills) and ≥ 8 m at 8563 and 7066 cal yr BP (Larsemann Hills) are over-predicted by some of the glacial isostatic adjustment models considered here, suggesting that assumptions relating to the magnitude and timing of regional ice loss since the Last Glacial Maximum may need revising. In the Vestfold Hills and Rauer Islands the final deglacial sea-level rise was almost exactly cancelled out by local rebound between 9411-5967 cal yr BP and this was followed by a near exponential decay in relative sea-level. In the Larsemann Hills the sea-level data suggest that the rate of ice retreat in this region was not uniform throughout the Holocene. Swath bathymetric surveys of the benthic seafloor topography show the presence of multiple offshore basins. These are a priority for further study as those free of grounded ice should provide precise constraints on relative sea-level rise and ice sheet history during the most rapid phases of the last major deglaciation.
... The rapid increase in total chls and total carotenoids indicates a quick colonization of the lake by cyanobacteria, diatoms and green algae following isolation (Fig. 8). The microbial turnover following lake isolation is similar to patterns observed from other Antarctic regions, such as the Larsemann Hills (Verleyen et al. 2004), and is characterized by an increase in brackish-water diatom species (N. phyllepta, Craspedostauros laevissimus (West & West) Sabbe and T. marginulata; Fig. 6), a rapid increase in cyanobacteria-derived pigments, the appearance of diatom-and green algae-related pigments (Fig. 8), and the subsequent establishment of a freshwater diatom community (Fig. 6). ...
Palaeoclimate changes, such as the Medieval Climate Anomaly and the Little Ice Age, are well-defined in the Northern Hemisphere during the past 2000 years. In contrast, these anomalies appear to be either absent, or less well-defined, in high-latitude regions of the Southern Hemisphere. Here, we inferred environmental changes during the past two millennia from proxies in a sediment core from Mago Ike, an East Antarctic lake in Skarvsnes (Lützow Holm Bay). Variations in lake primary production were inferred from fossil pigments, sedimentological and geochemical proxies and combined with absolute diatom counts to infer past diatom productivity and community changes. Three distinct stratigraphic zones were recognized, resulting from a shift from marine to lacustrine conditions with a clear transition zone in between. The presence of open-water marine diatoms indicates a coastal zone seasonally free of sea ice between c. 2120–1500 cal yr bp. Subsequently, the lake became isolated from the ocean due to isostatic uplift. Freshwater conditions were established from c. 1120 cal yr bp onwards after which the proxies are considered highly sensitive to temperature changes. There is no evidence for a Medieval Climate Anomaly, Little Ice Age or twentieth century warming in our lake sediment record suggesting that studies that have imposed Northern Hemisphere climate anomalies onto Southern Hemisphere palaeoclimate records should be treated with caution.
... Shennan et al. 2000), Greenland (e.g. Long et al. 1999Long et al. , 2008Bennike et al. 2002;), Iceland (Lloyd et al. 2009), Canada ( Miousse et al. 2003;Hutchinson et al. 2004;Smith et al. 2005), Russia (Corner et al. 2001) and Antarctica ( Zwartz et al. 1998;Verleyen et al. 2004;Bentley et al. 2005). ...
The main purpose of this work has been to describe the relative sea-level history in two areas of Norway with high accuracy through time and space, by collecting and interpreting new field data from isolation basins. This method offers a unique opportunity to reconstruct shoreline displacement along the Norwegian coastline, but has previously been employed only in a few regions. Much of the presented work focuses on Finnmark, perhaps the region in Norway where the most comprehensive and detailed reconstructions have been made, but also a region virtually devoid of chronological data. A site well inside Hardangerfjorden has
also been studied, where a rare cluster of isolation basins render it possible to produce the first precisely dated sea-level curve from a fjord site in Norway. A secondary objective has been to use lake stratigraphy to map and date deglaciation and tsunami history. Lake basins often provide continuous sequences that hold complete archives of geological events, rather than scattered traces that can be found in surface deposits.
Records of environmental changes, as well as tsunami erosion and deposition in near-shore basins, can therefore be found. Recent mapping of the seafloor has shown that several large slides have occurred at the Norwegian continental margin during the Holocene. Besides the much studied Storegga event, it is unknown whether tsunamis were triggered by these slides. Lakes that were close to sea level at tsunami time are likely to hold traces of such events.
... A similar increase of A. oligotrophenta (described as A. veneta and A. veneta var. capitata) was observed in the sediments of the coastal brackish Pup Lagoon at Larsemann Hills and interpreted as indicating saline lacustrine conditions following isolation (Gillieson, 1991; Verleyen et al., 2004). The upper sediments of Pup Lagoon are characterized by an ubiquitous cyanobacterial mat that is also evident throughout recent non-marine sediments of L. Skallen. ...
The paleolimnology of two lakes which were isolated as a result of the crustal uplift during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica were studied. The focus was on temporal variations in the biogeochemical composition of sediment cores recovered from Lake Skallen at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine settings, as indicated by analyses of C and N contents, nitrogen isotopic compositions (d 15 N), and major element concentrations. Changes in the dominant primary producers during the marine–lacustrine transition (marine diatom to cyanobacteria) at L. Skallen was clearly revealed by biogenic opal-A, diatom assemblages, and molecular signature from denaturing gradient gel electrophoresis (DGGE) with 16S ribo-somal RNA (rRNA) gene analysis. Radiocarbon dating of acid-insoluble organic C suggested that the environ-mental transition from marine to fresh water occurred at 2940 ± 100 cal yr BP at L. Skallen and 1060 ± 90 cal yr BP at L. Oyako. Based on these data, a mean crustal uplift rate of 3.2 mm yr À1 is inferred for the history of marine–lacustrine transition via brackish conditions. The geological setting causing glacio-isostatic uplift was the primary factor in controlling the transition event in sedimentary and biological facies.
... Within Diatom Zone 2 (68e54 cm) the transition from marine sea ice sub-surface communities to freshwater taxa was complete by 65e64 cm, 7165 (7280e7030) cal yr BP. Navicula phyllepta was relatively abundant in this transition zone and has been recorded in similar isolation basin transitions in east Antarctica (Verleyen et al., 2004(Verleyen et al., , 2005. The freshwater diatom community was highly variable between 65 and 54 cm with a succession from communities dominated by Pinnularia microstauron, to assemblages dominated by Navicula veneta and Planothidium quadripunctatum, culminating in a flora in which Gomphonema spp. ...
... Within Diatom Zone 2 (68e54 cm) the transition from marine sea ice sub-surface communities to freshwater taxa was complete by 65e64 cm, 7165 (7280e7030) cal yr BP. Navicula phyllepta was relatively abundant in this transition zone and has been recorded in similar isolation basin transitions in east Antarctica (Verleyen et al., 2004(Verleyen et al., , 2005. The freshwater diatom community was highly variable between 65 and 54 cm with a succession from communities dominated by Pinnularia microstauron, to assemblages dominated by Navicula veneta and Planothidium quadripunctatum, culminating in a flora in which Gomphonema spp. ...
The Antarctic Peninsula is one of the fastest-warming regions on Earth, but its palaeoenvironmental history south of 63° latitude is relatively poorly documented, relying principally on the marine geological record and short ice cores. In this paper, we present evidence of late-Quaternary environmental change from the Marguerite Bay region combining data from lake sediment records on Horseshoe Island and Pourquoi-Pas Island, and raised beaches at Horseshoe Island, Pourquoi-Pas Island and Calmette Bay. Lake sediments were radiocarbon dated and analysed using a combination of sedimentological, geochemical and microfossil methods. Raised beaches were surveyed and analysed for changes in clast composition, size and roundness. Results suggest a non-erosive glacial regime could have existed on Horseshoe Island from 35,780 (38,650–33,380) or 32,910 (34,630–31,370) cal yr BP onwards. There is radiocarbon and macrofossil evidence for possible local deglaciation events at 28,830 (29,370–28,320) cal yr BP, immediately post-dating Antarctic Isotopic Maximum 4, and 21,110 (21,510–20,730 interpolated) cal yr BP coinciding with, or immediately post-dating, Antarctic Isotopic Maximum 2. The Holocene deglaciation of Horseshoe Island commenced from 10,610 (11,000–10,300) cal yr BP at the same time as the early Holocene temperature maximum recorded in Antarctic ice cores. This was followed by the onset of marine sedimentation in The Narrows, Pourquoi-Pas Island, before 8850 (8480–9260) cal yr BP. Relative sea level high stands of 40.79 m above present at Pourquoi-Pas Island and 40.55 m above present at Calmette Bay occurred sometime after 9000 cal yr BP and suggest that a thicker ice sheet, including grounded ice streams, was present in this region of the Antarctic Peninsula than that recorded at sites further north. Isolation of the Narrows Lake basin on Pourquoi-Pas Island shows relative sea level in this region had fallen rapidly to 19.41 m by 7270 (7385–7155) cal yr BP. Chaetoceros resting spores suggest high productivity and stratified surface waters in The Narrows after 8850 (9260–8480) cal yr BP and beach clasts provide evidence of a period of increased wave energy at approximately 8000 yr BP. Lake sediment and beach data suggest an extended period of regional warming sometime between 6200 and 2030 cal yr BP followed by the onset of Neoglacial conditions from 2630 and 2030 cal yr BP in Narrows Lake and Col Lake 1, respectively. Diatom and δ13C vs C/N and macrofossil evidence suggest a potential increase in the number of birds and seals visiting the Narrows Lake catchment sometime after 2100 (2250–2000) cal yr BP, with enhanced nutrient enrichment evident after 1150 (1230–1080) cal yr BP, and particularly from c. 460 (540–380) cal yr BP. A very recent increase in Gomphonema species and organic carbon in the top centimetre of the Narrows Lake sediment core after c. 410 (490–320) cal yr BP, and increased sedimentation rates in the Col Lake 1 sediment core, after c. 400 (490–310) cal yr BP may be a response to the regional late-Holocene warming of the Antarctic Peninsula.
... Palaeolimnological research has been carried out in several East Antarctic coastal oases including the Vestfold Hills (e.g., Roberts and McMinn 1999; Roberts et al. 1999; Roberts et al. 2001a), Bunger Hills (e.g., Roberts et al. 2000), Larsemann Hills (e.g., Hodgson et al. 2001; Verleyen et al. 2004a, b, 2005a, b; Hodgson et al. 2005; Squier et al. 2005; Hodgson et al. 2006), Amery Oasis (Wagner et al. 2004) and Windmill Islands (e.g., Roberts et al. 2004). In closed lake systems the water chemistry responds quickly to changes in the balance between precipitation, evaporation from the catchment and open water, and sublimation loss from the frozen ice surface (Spaulding and McKnight 1999; Roberts et al. 1999; Verleyen et al. 2003) leading to episodes of increased salinity during dry/warmer periods and decreased salinity during wet/cooler periods. ...
Research in East Antarctica has shown several recent environmental changes that may be linked to human impacts on climate. In order to detect the influence and context of these changes on coastal aquatic ecosystems we examined lake sediment cores from three lakes in the Windmill Islands, East Antarctica; Beall Lake, Holl Lake and ȁ8Lake Mȁ9. Cores were sectioned at␣2.5mm intervals. Their diatom species composition was examined to detect changes in lake salinity using a diatom-salinity transfer function, and their algal pigment content was examined to detect photoautotrophic community responses to environmental change. Results showed that Holl Lake originated in a depression exposed by Holocene recession of the continental ice sheet and that Beall Lake and Lake M originated as isolated marine basins formed by changes in relative sea level. A general late Holocene trend of declining lake salinity was evident in all three lakes, interrupted by one short-term high salinity event in Beall Lake. This is consistent with a long-term positive moisture balance. This general decline in salinity has been followed by a remarkable recent rapid increase in salinity in all three lakes in the last few decades. We speculate that this rapid increase in salinity might be linked to changes taking place in the region including feedbacks resulting from decreasing sea ice extent as recorded in the nearby Law Dome ice core, and positive feedbacks in the catchments whereby reduced snow cover has led to decreased albedo, which in turn has caused increased evaporation and sublimation. Collectively these changes have shifted the lakes across a threshold from positive to negative moisture balance. A minor, but not rapid shift in the abundance of diatom pigments relative to pigments from green algae and cyanobacteria was also detected suggesting that some changes in photoautotrophic community composition have occurred. Measurements of modern nutrient levels are also higher than would be expected in Beall Lake and Holl Lake, given the extremely low sediment accumulation rates. This may be associated with a c. 300% increase in the population of Adélie penguins in the Windmill Islands recorded since the 1950s, or may a first signs of a rapid increase in catchment development and associated lake productivity as experienced in Antarctic and Arctic lakes subject to recent rapid regional warming. The most marked feature of the records is the rapid increase in salinity in all three lakes in␣the last few decades, which has occurred in lakes both with and without resident penguin populations.
... In order to interpolate the ages of different layers in the cores, a linear sedimentation rate was assumed. Marine and freshwater transitions were identified using a combination of sedimentology (Hodgson et al., 2001), diatoms (Verleyen et al., 2004a,b), and pigments (Squier et al., 2002). Sill elevations of the lakes were surveyed by the Australian Antarctic Data Centre with a spot-elevation accuracy of b0.5 m. ...
We present a relative sea-level (RSL) history, constrained by AMS radiocarbon-dated marine–freshwater transitions in isolation basins from a site adjacent to the Lambert Glacier, East Antarctica. The RSL data suggest an initial ice retreat between c. 15,370 and 12,660 cal yr B.P.. Within this period, meltwater pulse IA (mwp IA, between c. 14,600–14,200 and 14,100–13,700 cal yr B.P.) occurred; an exceptionally large ice melting event, inferred from far-field sea-level records. The RSL curve shows a pronounced highstand of approximately 8 m between c. 7570–7270 and 7250–6950 cal yr B.P. that is consistent with the timing of the RSL highstand in the nearby Vestfold Hills. This is followed by a fall in RSL to the present. In contrast to previous findings, the isolation of the lakes in the Larsemann Hills postdates the isolation of lakes with similar sill heights in the Vestfold Hills. An increase in RSL fall during the late Holocene may record a decline in the rate of isostatic uplift in the Larsemann Hills between c. 7250–6950 and 2847–2509 cal yr B.P., that occurred in response to a documented mid-Holocene glacier readvance followed by a late-Holocene retreat.
... Recent evidence that some east Antarctic coastal oases remained ice free through the LGM (Gore et al., 2001; Hodgson et al., 2001a) has highlighted an opportunity to reconstruct longer-term environmental changes by examining lake-sediment records. These changes can be inferred using the physical, biological and biogeochemical proxies that have already been applied in east Antarctic Holocene environmental reconstructions (Hodgson et al., 2001a; Verleyen et al., 2004b, c). In this study we present a reconstruction and comparison of likely-MIS5e and late Holocene (MIS1) interglacial environments in one east Antarctic oasis using multiple proxies (geochronology, sedimentology, biological and biogeochemical markers) in a lake-sediment core. ...
We reconstruct terrestrial and freshwater environments of the last two Quaternary interglacials in coastal east Antarctica by examining multi-proxy evidence in a lake sediment core. The record, from Progress Lake in the Larsemann Hills consists of two discrete sediment units. The lower unit contains the first known evidence of Antarctic coastal environments during a previous interglacial, likely to be MIS5e. Biogeochemical, biological and sedimentological climate proxies revealed a productive biological community and an active hydrological regime, consistent with the warmer conditions detected in continental ice cores at this time. The diatom assemblage was similar to that currently found in the sub- and maritime-Antarctic biome and included some sub-Antarctic endemic taxa that have not previously been reported from east Antarctica. This suggests southward expansion of the sub-Antarctic diatom biome during MIS5e. Mosses were also present in the lake or the catchment but are rare in the region today. Two discrete periods of enhanced productivity show that the MIS5e environment was not stable. MIS5e ended abruptly with a rapid transition to glacial conditions, the lake was covered by a layer of firnified snow and ice, and phototrophic biological activity ceased for a period of c. 90,000 years. The upper unit was deposited in MIS1 after 3470–3687 cal yr BP after phototrophic biological production resumed. Lower species diversity, pigment production, an Antarctic continental diatom assemblage and an absence of moss layers suggest cooler conditions during MIS1.
• Lakes and ponds along the Antarctic coastline provide an opportunity for palaeoclimate reconstructions to complement ice core records from the interior of the continent, including via their diatom records.
• Diatom palaeoecological studies in remote Antarctica are partially undermined by uncertainty concerning the relative influence of climate, water quality and substrate on diatom species assemblages.
• The relative abundance and distribution of diatoms across a range of substrates and water depths were analysed from nine lakes in the coastal ice-free regions of Lützow-Holm Bay, East Antarctica.
• Specific conductivity and sample position (whether from the shallow, littoral zone, or from deeper parts of the lake) were identified as significant variables in explaining diatom distribution, using non-metric multidimensional scaling and regression tree analysis to identify statistically significant groupings of diatom assemblages and associated environmental variables.
• In contrast to the significant difference between the diatom assemblages from the shallow littoral region and the lake floor at most sites, the diatom flora from different substrates in the littoral zone were not significantly different, which may be related to the extent of ice cover.
• Humodophila australis was the most common species in the lakes with lowest specific conductivity, whereas Halamphora vyvermaniana was associated with lake-floor habitats and Psammothidium papilio with samples from littoral zones at several sites.
• These observations hold significance for the interpretation of lake sediment diatom assemblages in Lützow-Holm Bay as archives of past climate and indicate that sampling strategies should consider a range of locations in lakes, with samples from the lake floor prioritised for the interpretation of sediment core diatom records.
The geomorphological settings of the lakes in the coastal oases of East Antarctica play a significant role in the lake’s response to the local and regional environment. A 63-cm radiocarbon-dated sediment core spanning between 18.7 and 7.2 cal ka BP was retrieved from Discussion Lake, Larsemann Hills of East Antarctica in order to understand the pathways of sediment transport and deposition and the mechanisms involved in response to changing environmental settings. This was achieved by analyzing the sedimentary sequence of this coastal lake for its grain size (sand-silt-clay) and organic matter content variations. Two cluster zones were identified viz., LZ1 (18.7 to 8.2 cal ka BP) and LZ2 (8.2 to 7.7 cal ka BP). LZ1 was dominated by fine-grained sediments (clay-silt), indicating wind and low meltwater influx influenced deposition of higher silt content. In addition, the lake during this period was in a moated or partially ice-free phases. On the other hand, coarser grains (sand) were predominant in LZ2 suggesting increased flux of the meltwater to the ice-free lake. Thus, the distinct shift in the sedimentary grains fractions (finer-to-coarser), indicated a change in environmental conditions of the lacustrine system, i.e., from an ice-covered lake to an ice-free lake in response to the regional warming trends and local geomorphological features. Furthermore, the environmental conditions, proximity of the lakes to coast or the ice-sheet, elevation and area, defines the sedimentological characteristics of the lake.
We studied Holocene paleolimnological changes inferred from multi-proxy data set of CNS elements, biomarkers and microscopic observation of microalgae and cyanobacteria in sediment cores from Rundvågshetta lakes (Maruwanminami-ike and Maruwan o-ike) in the Soya Coast region of East Antarctica, along with sedimentary facies and AMS ¹⁴ C dating. They are discussed with paleoenvironmental changes, transition ages and glacio-isostatic uplift rates in the Soya Coast region and East Antarctica. Ages of the Maruwanminami-ike core (MwS4C-01, length 147 cm) and Maruwan-oike (Mw4C-01, length 226 cm) ranged from 1,230-5,010 cal BP) and 2,240-5,700 cal BP, respectively. Reservoir effects of the Rundvågshetta lakes were very high which may be due to the influence of dead carbon in glacially eroded marine sediments and base rocks. Average sedimentation rates of Lakes Maruwanminami-ike and Maruwan-oike were 0.389 and 0.649 mm/yr, respectively. Crustal uplift rates of Lakes Maruwanminami-ike and Maruwan-oike determined by sedimentary facies, green sulfur bacterial biomarkers and diatoms were estimated to be 8.24 and 8.25 mm/yr, respectively. Coastal marine environment: Maruwanminami-ike (147-72.5 cm, 5,010-2,590 cal BP) and Maruwan-oike (226-47.2 cm, 5,700-3,190 cal BP) were characterized by low biological production with the predominance of diatoms. Transition period of stratified brackish lake environment: Maruwanminami-ike (72.5-65.6 cm, 2,590-2,500 cal BP) and Maruwan-oike (47.2-28.8 cm, 3,190-2,890 cal BP) were characterized by stratified conditions with marine water overlain by freshwater, and a chemocline developed together with an anoxic layer in the bottom of photic zone. Freshwater lake environment of Maruwanminami-ike (65.6-0 cm, 2,500-1,230 cal BP) was characterized by high biological production by cyanobacteria (e.g. Leptolyngbya spp.) and green algae (e.g. Comarium clepsydra) with some contribution of diatoms, while that of Maruwan-oike (28.8-0 cm, 2,890-2,240 cal BP) was very low biological production. The marine to terrestrial transition ages of raised beaches and isolated basins in the Saya Coast region ranged from 970 to 9,290 yr BP with an average of 3,660±1,520 yr BP (standard deviation) suggesting that major warm periods in the region are the middle Holocene. Glacio-isostatic uplift rates of raised basins and isolated basins in the Soya Coast region ranged from 0.19 to 4.40 mm/yr with an average of 2.0 ± 0.92 mm/yr which is similar to East Antarctica. Glacio-isostatic uplift rates of raised beaches are correlated with altitudes with a correlation coefficient of r ² = 0.724. Increasing crustal uplift rates with altitudes reflect continuous crustal uplifts in the Soya Coast region.
Holocene paleoenvironmental changes along the East Antarctic margin have been reconstructed using marine and lake sediment cores. Isolation basins in the coastal ice-free regions offer continuous sedimentary sequences to reconstruct marine-freshwater transitions and its environmental changes. In this study, we present the grain size (sand-silt-clay) and organic matter variations in a 51 cm radiocarbon-dated sediment core from Pup Lagoon, an isolation basin in Larsemann Hills (East Antarctica). The sediment core spans the last 6109 years and provides information on environmental changes in two different settings, i.e., (a) under the marine influence, and (b) as an isolated lake. Three cluster zones were identified viz., LZ1 (6109–2427 y BP: marine environment), LZ2 (2427–2101 y BP: transition zone) and LZ3 (2101–116 y BP: freshwater environment). Fine grain sediments (silt) are dominant in LZ1, indicating a strong hydrodynamic energy conditions affected by tidal currents with low organic matter. Higher sand content during the transition period (LZ2) indicates the strongest hydrodynamic condition and sediment deposition from sea ice. The increasing trend of OM (cyanobacterial benthic mat) beginning at ∼ 2101 y BP suggests the isolation of the lake. The highest fine grained sediments (silt-clay) in LZ3 suggests lowered meltwater derived detritus in response to mild austral summer conditions during the Late Holocene.
Geomorphic reconstructions of the East Antarctic Ice Sheet history across Antarctica suggest diachronous and varying retreat patterns with changing climate. However, little is known of how terrestrial environments responded to these climate changes because the continental ice sheet covered most Antarctic coastal oases during the Last Glacial Maximum (LGM), eliminating terrestrial records. In this study, the environmental history spanning the last 25,400 years was reconstructed using geochronology, lithology, rock magnetism and geochemistry to understand the effect of glacial–deglacial climate variations on surface processes and Mochou Lake ecology. During the last glacial period (25.4 to 18.8 cal. kyr BP), intensified winds and the freeze-thaw action of ice actively weathered the high elevation western catchment that was a dominant sediment source to the lake. The glacial environmental conditions induced a persistent perennial lake ice-cover resulting in anoxia, low sedimentation, primary production and weak brackish conditions. Progressively, as deglacial conditions augmented around 18.8 cal. kyr BP, increased catchment meltwater flow enhanced sediment transport and also transformed the lake into a freshwater basin, although perennial ice-cover still prevailed. Further, the biotic development of the lake began later in the Mid-Holocene as compared to other lakes in the region, wherein the seasonal lake ice cycle and/or ice moat developed. Weak chemical weathering and pedogenesis also commenced in the catchment in response to the warming climate trend. This delayed response to the Holocene warming was possibly due to the local cooling effect of the Dälk Glacier's discharge that also led to sea-ice persistence in the Prydz Bay. This study also provides further evidence that parts of the Larsemann Hills remained free of erosive grounded ice during the LGM and subsequent deglaciation. The Mirror Peninsula, specifically, escaped ice overriding despite being enclosed by the Dälk Glacier, Lake Nella ice lobe and Amery Ice Shelf.
Lakes from the coastal oasis of Larsemann Hills respond to changes in regional climate. They are mainly influenced by the ice-sheet dynamics and regional eustatic variation based on their proximity to either of them or both. The sedimentary sequences of the ice-free regions of Antarctica offer unique climate records (lake sediment deposits). Here, we present the evolution of a lake reconstructed from its sedimentary sequence. A 60 cm long radiocarbon-dated sediment core spanning the last 11.8 kyr from Lake LH73 located in Broknes Peninsula of Larsemann Hills is studied for grain size fractions, magnetic susceptibility, and diatom abundance. Based on the diatom and grain fraction data, it is inferred that the lake persisted as a proglacial lake during the early-Holocene (11.8 to 7.2 ky BP) dammed by ice-sheet towards the south. The lake level was at least 3 m higher than the present level (4 m) as inferred from the diatom transfer function owing to the presence of ice dam. The retreat of the ice-sheet and the collapse of the ice dam between 7.2 and 7 ky BP resulted in the lake transitioning to an isolated lake with the lake level attaining current level (4 m). As a consequence, the catchment area increased and the lake received meltwater from the snowbanks hence largely modulating the sedimentary process. The absence of glacial clay from 5 ky BP suggests that the lake was cut-off from the glacial input. The appearance of diatom at ~ 8.6 ky BP indicates the establishment of optimal condition for productivity in the lake ecosystem. Stauroforma inermis and Plannothidium quadripunctatum (Psammothidium abundans) dominates between 7 ky BP till present (11.8 to 7 ky BP), responding to lake level variation. Ice-sheet retrieval and ablation led to transition of proglacial-to-isolated lake leading to shallowing of the lake as reflected in diatom assemblage changes.
The Schirmacher Oasis and Larsemann Hills are among the few significant ice free areas of East Antarctica that are conspicuous due to presence of more than a hundred melt water lakes each, preserving the signatures of climatic variation and deglaciation history since Last Glacial Maximum (19 to 24 ky BP) and beyond. There are evidences, recorded in the lake sediments of low lying Larsemann Hills, of marine transgression due to variation in sea level, isostatic upliftment and close vicinity of the Hills to the marine environment. The Schirmacher Oasis, on the other hand has preserved various landforms-both erosional and depositional- typical of a periglacial environment along with proglacial lakes (incorporating signals of ice-sheet dynamics) and epishelf lakes (signatures of marine influence) .
The Antarctic Ice Sheet (AIS) is one of the largest potential contributors to future sea-level changes. Recently, an acceleration of AIS volume loss through basal melting and iceberg calving has been reported based on several studies using satellite observations, including radar altimetry, interferometer, and gravity measurements. A recent model that couples ice sheet and climate dynamics and incorporates hydrofracturing mechanism of buttressing ice shelves predicts a higher sea-level rise scenario for the next 500 years. However, the calibration and reproducibility of the sea-level rise projection from these models relies on geological sea-level reconstructions of past warm intervals. This suggests that a highly reliable reconstruction of the past AIS is essential for evaluating its stability and anticipating its contribution to future sea-level rise. In particular, a relative sea-level reconstruction in East Antarctica is the key to solving the problems and refining future projections. The current understanding of sea-level change along the East Antarctic margin is reviewed, including Glacial Isostatic Adjustment (GIA) effects, and a new strategy is proposed to address this topic based on seamless sediment coring from marine to lake in the East Antarctic margin. This project will provide essential data on AIS change since the last interglacial period.
Introduction The polar regions, both Arctic and Antarctic, show strong evidence of climate change affecting freshwater species, communities, and ecosystems, and are expected to undergo rapid and continued change in the future (IPCC, 2007). Diatoms in the freshwater and brackish habitats of inland waters of the Antarctic provide valuable records of their historic and modern environmental status. Antarctic habitats also contain a unique biodiversity of species many of which are found nowhere else on Earth. In this chapter, we review investigations using diatoms as indicators of environmental change in Antarctic and subantarctic island habitats, including lakes and ponds, streams and seepage areas, mosses and soils, cryoconite holes, brine lakes, and remarkable subsurface glacial lakes. The Antarctic continent holds the vast majority of the Earth’s freshwater, but the water is largely inaccessible because it is in the form of ice. Life is dependent upon liquid water, a substance scarce in Antarctica. Less than 0.4% of the continent is ice free, and it is within these ice-free regions that freshwater lakes and ephemeral streams form, fed by the melting of snow and glacial ice and occasional precipitation. These ice-free regions are located primarily near the Antarctic coastline (Figure 14.1). Of these regions, the “desert oases” of East Antarctica are considered to be the coldest, driest regions on Earth. In the limited parts of these oases where liquid water is available, even if present for only a few short weeks of the year, there is life (McKnight et al., 1999).
We collected two lake sediment cores (MC and DM) from the East Antarctic region for analysis of biogenic silica and other biogeochemical parameters (e.g., organic matter, C, N, S, H). Based on synthetically comparative research, we focused on the potential application of biogenic silica (BSi) for the reconstruction of paleo-primary productivity in the East Antarctic lakes. Analytical results showed that a large number of diatoms were well preserved in the freshwater lake sediments, and that concentrations of biogenic silica displayed notable fluctuations over different water depths. The content of biogenic silica had a consistent profile over water depth, and this pattern changed with organic matter, reflecting their potential as eco-environmental proxies. Low lev-els of BSi and organic matter indicated reduction of lake algal production, and corresponded to decreased lake primary productivity. Due to the fragile ecosystem state and limited contribution of terrestrial organic matter in the East Antarctic lakes, the contents of biogenic silica in the lacustrine sediments can sensitively indicate the evolutionary history of paleo-primary productivity. Overall, BSi is an ideal proxy for the reconstruction of past eco-environmental change recorded in the lacustrine sediments on East Antarctica.
Isolation basins are natural topographic depressions that at various times in their history may be connected to or isolated from the sea by changes in relative sea-level (RSL). They provide a valuable source of data for tracking large scale (tens of meters), millennial-scale changes in RSL, as well as quiet-water depositional environments where abrupt changes caused by tsunami, iceberg roll or storms may be recorded. In this paper we review isolation basins as sources of RSL data with a particular focus on their use in Greenland to constrain the Holocene history of the ice sheet. A new RSL curve from Disko Fjord, West Greenland is presented, which shows that local ice free conditions were established at c. 11 k cal. yr BP, after which RSL fell rapidly from a marine limit at c. 80 m to reach close to present sea-level by c. 4 k cal yr BP. We compare this record with other isolation basin RSL data from six other sites in Disko Bugt and note a strong northwest/southeast differential rebound across the area during the early and mid-Holocene that reflects variations in ice load history. We compare the Disko Bugt data with other previously published isolation basin RSL records from Sisimiut (central West Greenland), Nanortalik (south Greenland) and Ammassalik (southeast Greenland). RSL fell below present during the early-Holocene at Nanortalik (c. 10 k cal yr BP) and during the mid to late Holocene elsewhere before rising to present. These differences reflect variations in the timing and amount of Greenland ice load change since the last glacial maximum, as well as non-Greenland processes, notably the collapse of the Laurentide forebulge and changes in ice equivalent sea-level. Isolation basin data have relatively small age and height uncertainties compared with other RSL indicators, enabling them to resolve between different earth and ice sheet models, especially during periods of large ice load and RSL change.
Both ground-based and satellite data show that parts of Antarctica have entered a period of rapid climate change, which already affects the functioning and productivity of limnetic ecosystems. To predict the consequences of future climate anomalies for lacustrine microbial communities, we not only need better baseline information on their biodiversity but also on the climate-related environmental factors structuring these communities. Here we applied denaturing gradient gel electrophoresis (DGGE) of the small subunit ribosomal DNA (SSU rDNA) to assess the genetic composition and distribution of Cyanobacteria and eukaryotes in 37 benthic microbial mat: samples from east Antarctic lakes. The lakes were selected to span a wide range of environmental gradients governed by differences in lake morphology and chemical limnology across 5 ice-free oases. Sequence analysis of selected DGGE bands revealed a high degree of potential endemism among the Cyanobacteria (mainly represented by Oscillatoriales and Nostocales), and the presence of a variety of protists (alveolates, stramenopiles and green algae), fungi, tardigrades and nematodes, which corroborates previous microscopy-based observations. Variation partitioning analyses revealed that the microbial mat community structure is largely regulated by both geographical and local environmental factors of which salinity (and related variables), lake water depth and nutrient concentrations are of major importance. These 3 groups of environmental variables have previously been shown to change drastically in Antarctica in response to climate change. Together, these results have obvious consequences for predicting the trajectory of biodiversity under changing climate conditions and call for the continued assessment of the biodiversity of these unique ecosystems.
The history of glacial advances and retreats of the East Antarctic ice sheet during the Holocene is not well-known, due to limited field evidence in both the marine and terrestrial realm. A 257-cm-long sediment core was recovered from a marine inlet in the Rauer Group, East Antarctica, 1.8km in front of the present ice-sheet margin. Radiocarbon dating and lithological characteristics reveal that the core comprises a complete marine record since 4500yr. A significant ice-sheet expansion beyond present ice margins therefore did not occur during this period.
Diatoms were studied in sediment cores SKPC-10, SKPC-08, SKPC-01 and LINK-1, retrieved from the Faeroe Islands fjords and the adjacent waters of the Northern Atlantic Ocean. The diatom record encompasses the Holocene sediments beginning from the middle Holocene. The record shows distinct temporal changes in species composition and is dominated by marine forms. Earlier studies showed that inundation of the fjords by Northern Atlantic waters took place about 7700–6400 years BP. Saline waters inflow forced drastic changes in the diatom species composition in the study area. Unlike other areas of the Northern Atlantic, the Faeroe Islands fjords sediments are characterized by well preserved diatom floras. The diatoms are predominantly of planktonie origin (Paralia sulcata, Thalassiosira nordenskioeldii, Thalassionema nitzschioides, Thalassiosira angulata and Rhizosolenia hebetatd); however, the relatively shallow coring sites result in fairly abundant and diverse benthic flora (Odontella aurita, Grammatophora marina, Grammatophora angulosa var. islandica, Cocconeis costata, Rhabdonema minutum, and Rhabdonema arcuatum). A special focus of this paper is the distribution and taxonomy of the benthic marine taxa, either sediment dwelling or epiphytic.
A sediment core from Progress Lake, one of the oldest lacustrine sequences in East Antarctica, contains distinct zones dating from a previous interglacial (most likely Marine Isotope Stage 5e, c. 125–115 kyr BP) and the present interglacial (Marine Isotope Stage 1), separated by a transition zone representing when the lake became sub-glacial. Profiles of fossil pigments, determined using high performance liquid chromatography and liquid chromatography-tandem mass spectrometry, show distinct differences in the photoautotrophic community during these two interglacial periods. The first was dominated by algae and purple phototrophic bacteria, with periods of photic zone euxinia indicated by pigments from anoxygenic phototrophic bacteria. Specific chlorophyll a derivatives reveal periods when grazing pressure impacted significantly on the phytoplankton community. The virtual absence of pigments in the transition zone reflects severe restriction of photoautotrophic activity, consistent with the lake having become sub-glacial. Retreat of snow and ice in the late Holocene (3345 14C yr BP) allowed establishment of a less diverse primary producer community, restricted to algae and cyanobacteria. Grazers were severely restricted and oxidative transformation was more important than during the previous interglacial. The pigment data provide a unique and detailed insight in to the evolution of the lake ecology over an interglacial-glacial-interglacial transition and strong evidence that the Marine Isotope Stage 5e interglacial in this region of coastal East Antarctica was several degrees warmer than at present.
An 85-cm long sediment sequence from Mochou Lake on Mirror Peninsula in the Larsemann Hills, East Antarctica, was investigated for elemental geochemistry, biogeochemistry and strontium (Sr) isotopic composition in the acid-insoluble and acid-soluble fractions. The biogeochemical data showed that the freshwater lacustrine sediment originated after 2750 BP. The element Zn, Cu, F, P and Se fluxes displayed almost the same vertical distribution patterns, and their ratios over loss on ignition had strong positive correlations with each other, indicating a common source, probably from seabird droppings. The Sr isotopic compositions provided further evidence of the influence of seabirds on the freshwater lacustrine sediments. The 87Sr/86Sr ratios determined in the acid-soluble fraction were remarkably lower than those of the acid-insoluble fraction; with a bedrock 87Sr/86Sr signature, they were close to those of the marine-derived Sr and were negatively correlated with total amino acids. Using the ratio vs. depth profiles of P, Zn, Cu, Se, F, As, Cd and Ni fluxes over Al, we reconstructed the historical seabird population in the catchment area of Mochou Lake. During the past c. 2800 years, the seabird population has experienced substantial changes in the absence of human activity, and four troughs were identified. After comparison with the palaeoclimatic records and glacial advance and retreat history, the pronounced seabird population declines seem to be related to climatic deterioration.
The Late Quaternary climate history of the Larsemann Hills has been reconstructed using siliceous microfossils (diatoms, chrysophytes and silicoflagellates) in sediment cores extracted from three isolation lakes. Results show that the western peninsula, Stornes, and offshore islands were ice-covered between 30 000 yr BP and 13 500 cal. yr BP. From 13 500 cal. yr BP (shortly after the Antarctic Cold Reversal) the coastal lakes of the Larsemann Hills were deglaciated and biogenic sedimentation commenced. Between 13 500 and 11 500 cal. yr BP conditions were warmer and wetter than during the preceding glacial period, but still colder than today. From 11 500 to 9500 cal. yr BP there is evidence for wet and warm conditions, which probably is related to the early Holocene climate optimum, recorded in Antarctic ice cores. Between 9500 and 7400 cal. yr BP dry and cold conditions are inferred from high lake-water salinities, and low water levels and an extended duration of nearshore sea-ice. A second climate optimum occurred between 7400 and 5230 cal. yr BP when stratified, open water conditions during spring and summer characterised the marine coast of Prydz Bay. From 5230 until 2750 cal. yr BP sea-ice duration in Prydz Bay increased, with conditions similar to the present day. A short return to stratified, open water conditions and a reduction in nearshore winter sea-ice extent is evident between 2750 and 2200 cal. yr BP. Simultaneously, reconstructions of lake water depth and salinity suggests relatively humid and warm conditions on land between 3000 and 2000 cal. yr BP, which corresponds to a Holocene Hypsithermal reported elsewhere in Antarctica. Finally, dry conditions are recorded around 2000, between 760 and 690, and between 280 and 140 cal. yr BP. These data are consistent with ice-core records from Antarctica and support the hypothesis that lacustrine and marine sediments on land can be used to evaluate the effect of long-term climate change on the terrestrial environment. Copyright © 2004 John Wiley & Sons, Ltd.
Approximately 98% of the Antarctic continent is currently ice-covered and, except for subglacial lakes (Priscu and Christner 2004), possesses no liquid water environments. In contrast, the other 2% contains an extraordinary array of aquatic environments including ice-covered freshwater and saline lakes and ephemeral streams. Lakes are found mostly in coastal, ice marginal regions in the Antarctic (Doran et al. 1994). Because of the great differences in mean-annual temperature related to the locations of these aquatic systems (Fig. 1), the temporal extent of ice covers on the lakes varies greatly. There are lakes that are ice-covered for part of each year, while there are perennially ice-covered systems in the dry valleys region of Southern Victoria Land where only 'moats' (ie ice-free littoral zones) form during the warmest summers. Because ice cover greatly influences both the physical and biological processes occurring within lakes, the extent and thickness of ice cover is an extremely important parameter in the biogeochemistry of Antarctic lakes (Wharton et al. 1993, Fritsen and Priscu 1999). Paleolimnological investigations demonstrate that climate variations have greatly impacted the extent of ice cover, in addition to the overall hydrology of Antarctic lakes throughout the Holocene back into the Last Glacial Maximum (LGM) (Wilson 1964, Bird et al. 1991, Bjorck et al. 1996, Fulford-Smith and Sikes 1996, Gore et al. 1996, Lyons et al. 1998b, Hendy 2000). Much of the paleolimnological work from Antarctic lakes has recently been summarized by Hodgson et al. (2004) and Doran et al. (2004) and will not be repeated here. Some of the earlier work on Antarctic lakes illustrated its value in delineating changes in the hydrologic response to climate (Wilson 1964). The integration of paleolimnological data with more recent observations has provided important insights into how these lakes respond to climate change (eg Gibson and Burton 1996, allied with the work of Roberts et al. 2001 in the Vestfold Hills and Poreda et al. 2004, allied with Hendy 2000 in Taylor Valley, Victoria Land). Understanding the impact of climate on the hydrologic balance of Antarctic lakes, and in turn, the influence of hydrologic changes on the overall ecology of these systems is a major challenge to Antarctic limnologists. This will be especially true in the future period of anthropogenically-induced climate change. Kejna (2003) has recently reviewed the air temperature records from 34 stations around the Antarctic continent. The data span from 1958-2000 for 21 stations and for 1981-2000 for all the stations. In general, warming has occurred on the Antarctic Peninsula and in interior West Antarctica, with Faraday Station, on the west coast of the Peninsula having increased at a rate of 0.67°C per decade over the period 1958- 2000. Many of the coastal stations in East Antarctica also demonstrated an increase in temperature over the longer time interval. However, since 1981, many regions of the continent, especially in East Antarctica, have shown a cooling. For example, Casey shows a 0.82°C per decade decrease (Kejna 2003). There has also been a weakening of the warming rate on the Peninsula during the last 20 years. Because Antarctic lakes are so sensitive to both increases and decreases in temperature (ie Wilson 1964, Gibson and Barton 1996, Foreman et al. 2004), the direct monitoring of Antarctic lakes provides an excellent sentinel of climate change, especially as climate impacts the local hydrologic cycle. Climate variation and change are not the only factors affecting Antarctic lakes. The activities of mammal and bird populations also exert considerable influence on the physical, chemical and biological evolution of many Antarctic limnetic systems. Human activities can also be important in certain situations. For example, Heywood Lake, on Signy Island, has undergone eutrophication in the last 30 years because of input of nutrients from an expanding fur seal population within the catchment (Butler 1999). This has led to increased microbial abundance and changes in the structure of the ecosystem, with phytoplankton taxa more typical of polluted waters, as opposed to the more oligotrophic waters that existed in the 1970s and early 1980s (Butler 1999) before the fur seal population explosion. Eutrophication has led to longer periods of lake anoxia during winter thermal stratification and changes in seasonal biological patterns within the lake. Recent work in the Larsemann Hills has demonstrated that lakes impacted by human activities such as grey water and human waste discharge and even rock crushing by tracked vehicles have enhanced nutrient and total dissolved solid loads (Kaup and Burgess 2002). A comparison of human impacted catchments with catchments with little direct human activity indicates that the levels of dissolved nitrogen compounds were generally much higher in the human-influenced catchments. Salinities were also up to an order of magnitude higher in the human impacted catchments (Kaup and Burgess 2002). Monitoring the response of lake dynamics to changing climate has long been recognized as an important task (Wilson 1981). The linkage between changing climate and lake dynamics becomes even more complicated in lakes that are influenced by direct human impacts. Most investigations of Antarctic lakes have been conducted over limited time periods (1-3 years). Although these short-term studies have been extremely important in establishing base-line conditions, determining the taxa that are present, and understanding biogeochemical processes in the lakes, they are not conducive to establishing long-term limnological trends. Our paper focuses on studies resulting in long-term data comparisons that have produced information about biological and/or physical and chemical trends thought to be driven by changing climatic parameters. This focus greatly limits the resources available to compare long-term trends that do exist and historic information on Antarctic limnology because it eliminates numerous one-time studies of specific limnetic systems in various parts of the continent. (We differentiate between longterm and historic data by defining 'long-term' as relatively continuous records through time and 'historic' as data collected with time gaps between collections). In addition, this paper will not address trends in the epishelf lakes that exist on the continent especially in the Bunger Hills and Schirmacher Oasis regions (Bormann and Fritzsche 1995, Doran et al. 2000, Gibson and Andersen 2002). For information on epishelf lakes, see Gibson et al. this volume. Because of the important differences in the climate regimes within the Antarctic, we have separated our discussion into geographic regimes that have been used previously (Convey 2001).
The seasonal variations of limnological (water temperature, light availability, turbidity, and chlorophyll a concentration) parameters were recorded continuously from January 2004 to February 2005 at two freshwater lakes: Oyako-ike
and Hotoke-ike, Sôya Coast, East Antarctica. Water was in a liquid phase throughout the year, with temperatures ranging from
0 to 10°C. The maximum photosynthetically active radiation in Lake Oyako-ike was 23.16molm−2day−1 (at 3.8m) and Hotoke-ike was 53.01molm−2day−1 (at 2.2m) in summer, and chlorophyll a concentration ranged from ca. 0.5 to 2.5μgL−1 (Oyako-ike) and from ca. 0.1 to 0.8μgL−1 (Hotoke-ike) during the study period. Increase in chlorophyll a fluorescence occurred under dim-light conditions when the lakes were covered with ice in spring and autumn, but the signals
were minimum in ice-free summer in both the lakes. During spring and summer, as a result of decreasing snow cover, the chlorophyll
a concentration similarly decreased when PAR was relatively high, following periods of heavy winds. The autumnal and spring
increase occurred under different PAR levels (ca. 20-fold and 90-fold stronger, respectively, in autumn in both the lakes).
Differences in the autumn and spring increases suggest that the spring algal community is more shade-adapted than the autumn
algal community. Antarctic phytoplankton appears especially adapted to low-light levels and inhibited by strong light regimes.
The Rauer Group is an archipelago in Prydz Bay, East Antarctica. The ice-free islands and the surrounding shallow marine areas provide valuable archives for the reconstruction of the late Pleistocene and Holocene environmental and climatic history of the region. Two sediment records from two marine inlets of Rauer Group have been studied for their sedimentological, geochemical, and biological characteristics. Radiocarbon ages from one of the inlets indicate ice-free conditions within the last glacial cycle, probably during the second half of Marine Isotope Stage 3. Subsequent ice sheet coverage of Rauer Group during the Last Glacial Maxiumum (LGM) can be inferred from a till layer recovered in one of the basins. The inlets became ice-free prior to 11,200 cal yr BP, when biogenic sedimentation started. Deglacial processes in the catchments, however, influenced the inlets until ~ 9200 cal yr BP as evidenced by the input of minerogenic material. Marine productivity under relatively open water conditions indicates an early Holocene climate optimum until 8200 cal yr BP, which is followed by a cooler period with increased sea ice. Warmer conditions are inferred for the mid Holocene, when both basins experienced an input of freshwater between ~ 5700–3500 cal yr BP, probably due to ice-sheet melting and increased precipitation on the islands. Neoglacial cooling in the late Holocene since c. 3500 cal yr BP is reflected by an increase in sea ice in both inlets.
High performance liquid chromatography-mass spectrometry has permitted the identification of a homologous series of novel alkylsulfide derivatives of chlorophyll a containing between one and five carbon atoms, in sediment from a coastal Antarctic lake. The sulfur-containing compounds are present in varying abundance in stratigraphic horizons representing a phase when the lake was a marine basin. Throughout this marine phase photic zone anoxia is recorded by the presence of bacteriochlorophyll c and d-derivatives. Distributional variations between sulfurised and non-sulfurised chlorophyll a-derivatives throughout the sediment section studied indicate that the extent of sulfurisation is not controlled by chlorophyll a abundance alone.
We determined the mean crustal uplifting rate during the late Holocene along the Soya Coast, Lützow-Holm Bay, East Antarctica, by dating a marine-lacustrine transition recorded in lake sediments. We focused on temporal variations in the chemical composition of sediments recovered from Lake Skallen Oike at Skallen and Lake Oyako at Skarvsnes. Both sets of lake sediments record environmental changes associated with a transition from marine to lacustrine (fresh water) settings, as indicated by analyses of sedimentary facies for carbon and nitrogen contents, nitrogen isotopic compositions (15N/14N), and major element concentrations. Changes in the dominant primary producers during the marine-lacustrine transition were also clearly revealed by biogenic Opal-A, diatom assemblages, and gradient gel electrophoresis (DGGE) with 16S rRNA gene analysis. Geochronology based on radiocarbon dating of acid-insoluble organic carbon suggested that the environmental transition from saline to fresh water occurred at 2940±100 cal yr BP at L. Skallen and 1060±90 cal yr BP at L. Oyako. Based on these data and a linear approximation model, we estimated a mean crustal uplifting rate of 3.6 mm yr−1 for the period since the marine-lacustrine transition via brackish condition; this uplift is attributed to glacial-isostatic rebound along the Soya Coast. The geological setting was the primary factor in controlling the emergence event and the occurrence of simultaneous changes in sedimentary and biological facies along the zone of crustal uplift.
This paper presents preliminary relative sea level curves for the Marguerite Bay region and for the South Shetland Islands. The Marguerite Bay curve is constrained by both new and previously published 14C dates on penguin remains and shells, and on two isolation basins dating back to 6500 14C yr BP. Extrapolation back to the marine limit yields a minimum deglaciation date for Marguerite Bay of ca 9000 14C yr BP. Analysis of beach clasts suggests that there was a period of increased wave activity, perhaps related to a reduction in summer sea-ice extent, between ca 3500 and ca 2400 14C yr BP. The curve for the South Shetland Islands is derived entirely from published 14C dates from isolation basins and on whalebone, penguin bone and seal bone. The curve shows an initial relative sea level fall, which was interrupted by a period in the mid-Holocene when relative sea level rose to a highstand of between 14.5 and 16 m above mean sea level (amsl), before falling again.
Lake-sediment cores from Heywood and Sombre Lakes on Signy Island (South Orkney Islands), Antarctica, have yielded a conformable radiocarbon chronology for the Holocene and a high-resolution record of environmental change. The lakes share a common climate and geology but have distinct catchments. This provides an opportunity for using lake sediments to differentiate between local, within lake/catchment, events and those at a regional scale. Analyses of various biological and physical remains from the lakes suggest that both catchments have undergone considerable changes during the last 5700 years. Macrofossils (moss and crustacean remains) are more abundant in the late Holocene, being associated with a period of high sediment accumulation, which is related to diatom evidence for more nutrient-rich conditions at the sites. This is interpreted as a response to a Holocene‘climate optimum' at c. 3800–1300 14C yr BP. The record is consistent with other lake, ice and ocean core studies, although the climate optimum appears to have persisted for a longer period at Signy Island.
The Larsemann Hills area in Prydz Bay, East Antarctica, underwent low pressure granulite facies metamorphism about 1100 Ma ago. This peak metamorphic age is similar to that of large areas west of the Larsemann Hills, but contrasts with the Archaean age of the Vestfold Hills only 100 km to the northeast. The dominant rock types in the Larsemann Hills are metapelitic cordierite‐ and Fe‐Ti oxide‐rich gneisses and various leucogneisses. Felsic, garnet‐bearing, variably foliated ‘yellow gneiss’ (60% of outcrop) and the extremely cordierite‐rich ‘blue gneiss’ (10% of outcrop) constitute the two major metasedimentary units. Mafic dykes, charnockites and evidence of brittle deformation are absent, and there are minor orthogneisses as well as mafic two pyroxene gneisses that lack garnet and ultramafic rocks. These features distinguish the Larsemann Hills not only from the Archaean Vestfold Hills to the northeast, but also from the 1000 Ma old ‘transition zone’ in the Rauer Group and outcrops of similar age to the southwest.Three major deformation phases affected the Larsemann Hills area. The first deformation, D1, took place prior to and synchronously with the peak metamorphic event M1 and formed tight, isoclinal folds which cannot be resolved on a regional scale. The second deformation, D2, the major outcrop‐scale shortening deformation, took place at the time of decompression (M2) from the metamorphic peak, and subsequent minor deformation may have continued during cooling to the stable geotherm. The third deformation, D3, folded the Larsemann Hills gneisses into a large, knee‐shaped fold plunging steeply to the southwest. Overprinting of many textures by large porphyroblasts and granitic melts indicates that a thermal event (M3) or rapid increase in H2O activity affected the area after the pervasive ductile deformations. This event may correlate with D3 and may have been responsible for the excavation of the Larsemann Hills during the Palaeozoic.
Two sediment cores taken from Jaw lake (Bunger Hills, East Antarctica) were analysed for diatom composition and abundance. A diatom-salinity transfer function developed for the nearby Vestfold Hills was used to determine palaeosalinity reconstructions from the assemblages preserved in each of the cores. There is a large step-wise decrease in salinity in the second core from at least c. 4000 to c. 2000 uncorrected 14C yr BP. The salinity record from the first core starts at c. 3000 uncorrected 14C yr BP and is comparable with the salinity of the second core between c. 3000 and c. 2000 uncorrected 14C yr BP. Sudden lake water dilution in both cores at c. 1900 uncorrected 14C yr BP is followed by brief increases in lake water salinity between c. 1900 and c. 500 uncorrected 14C yr BP, after which gradual dilution to present occurs. This analysis of the local environmental history of this saline lake reveals a mid–late Holocene evolution of the lake basin similar to that documented from earlier marine and freshwater lacustrine sediments in the Bunger Hills. The high coherence of the independent sediment records suggests a robust general palaeosalinity reconstruction of the lake is achieved in addition to providing evidence for the fidelity of single sediment cores as useful and adequate representation of the palaeolimnological histories of Antarctic lakes.
Based on light and electron microscopical investigations, a new genus Craspedostauros is described for a group of marine biraphid diatoms previously placed in Stauroneis Ehrenberg. The genus Stauronella Mereschkowsky had been erected for one of these species, Amphiprora constricta sensu W. Smith, but Mereschkowsky's name cannot be used for nomenclatural reasons. Craspedostauros species can be recognized by the possession of cribrate areolae, a stauros that is usually narrower than the fascia, many girdle bands with double rows of cribrate areolae and two chloroplasts, fore and aft of the central cytoplasm, each with a central pyrenoid. The genus shows similarities in its pore structure and chloroplast type and arrangement to Mastogloia Thwaites ex W. Smith and Aneumastus Mann & Stickle, suggesting that it is more closely related to these than to other naviculoid genera with a stauros, i.e. Stauroneis, Staurophora Mereschkowsky, Meuniera Silva and Haslea Simonsen. The stauros is a feature that probably arose a number of times. A description of the genus and its currently recognized members is given, with a key to their identification. Four new species are described, the types of which have been deposited in the Natural History Museum, London. The status of Stauronella constricta var. linearis Mereschkowsky remains unclear in the absence of any material from the Black Sea. Some marine stauroneid diatoms that do not belong in Craspedostauros are briefly discussed.
Natural levels of ultraviolet (UV) radiation can harm organisms in shallow aquatic ecosystems in which concentrations of photoprotective dissolved organic carbon are low. These compounds can be removed as a result of acidic precipitation and climate changes, an effect which may have recently been manifested in up to 200,000 boreal lakes. Unfortunately, meteorological and biological monitoring studies are usually too brief to record the magnitudes of past changes in UV radiation fluxes and their effects. Here we demonstrate that certain fossil pigments in lake sediments can be used to document historical changes in the UV radiation environment of lakes. These pigments are produced by benthic algae when exposed to UV radiation and show sedimentary concentrations that are correlated to the depth of penetration of UV radiation within lakes. Analysis of fossil profiles from the sediments of two mountain lakes suggests that past UV radiation penetration has sometimes been-at least in these mid-latitude lakes-greater than dining the period of anthropogenic stratospheric ozone depletion.
A marine survey in Prydz Bay, provides an unparalleled view of glacigenic and marine sedimentation across Prydz Channel and Amery Depression during the Late Quaternary. Gravity cores and a suite of eight radiocarbon dates indicate that the Late Wisconsin Glacial Maximum (LGM) was associated with grounding of a palaeo-ice shelf along the periphery of Prydz Channel. Deposition in front of the grounding line was dominated by ice-rafting. A granulated facies, containing angular clay and diamicton clasts, was producd by a combination of regelation freezing, near to the grounding line, and remelting of this basal debris in the sub-ice shelf setting. Beneath these LGM marine deposits lie two key beds of diatom ooze that are distinct in size sorting and Pliocene diatoms. These “interstadial” units can be traced across most of the Prydz Channel, and are underlain by additional glacial marine units. Debris related to the Lambert Deep is distinct from detritus from eastern Prydz Bay and deposition of these two sources within the channel oscillated during the LGM. We suggest that coastal drainage systems contributed to a limited glaciation of the shelf during the LGM, rather than direct outflow via the Lambert/Amery system. It is proposed that shelf-wide glaciation is related to the duration of glacial sea level lowstands rather than the absolute magnitude of eustatic fall during such episodes.
Radiocarbon dating of marine, lacustrine or terrestrial biogenic deposits is the main technique used to determine when deglaciation of the oases of East Antarctica occurred. However, at many of the oases of East Antarctica, including the Schirmacher Oasis, Stillwell Hills, Amery Oasis, Larsemann Hills, Taylor Islands and Grearson Oasis, snow and ice presently forms extensive blankets that fills valleys and some lake basins, covers perennial lake ice and in places overwhelms local topography to form ice domes up to hundreds of square kilometres in area. Field observations from Larsemann Hills and Taylor Islands suggest that under these conditions, terrestrial and lacustrine biogenic sedimentation is neither widespread nor abundant. If similar conditions prevailed in and around the oases immediately following retreat of the ice sheet, then a lengthy hiatus might exist between deglaciation and the onset of widespread or abundant biogenic sedimentation. As a result, radiocarbon dating might be a clumsy tool with which to reconstruct deglaciation history, and independent dating methods that record emergence of the hilltops from the continental ice must be employed as well.
The Rauer Islands contain more than fifty shallow lakes and small ephemeral ponds. Despite their proximity to the Vestfold Hills - one of the most diverse and intensively studied lake districts of eastern Antarctica - the lakes of the Rauer Islands have remained undescribed. In this study the physical and chemical limnology and biology of ten lakes is presented and their species-environment relationships explored using multivariate statistics. Analyses of chemical and biological data indicate that the Rauer Islands form a distinct limnological province amongst the lakes of the Prydz Bay oases. Salinities range from hypo- to hyper-saline with an ionic order close to that of seawater. Deviance from this order indicates either an earlier origin for some of the most hypersaline lakes when compared with the Vestfold Hills, more rapid evaporation vs precipitation or differences in the sources of ions resulting from isostatic history. With fluctuating salinities, winter water temperatures below –10°C, seasonal ice and slush formation, desiccation and high levels of solar radiation, the lacustrine environment presents considerable abiotic challenges for biological survival. Results indicate that there is little or no planktonic flora in the lakes and no zooplankton were encountered. Despite this, analyses of pigments, diatoms and other micro-algae revealed an active and diverse benthic biota characterized by filamentous cyanobacteria with interstitial algae. Thirty-eight diatom taxa, and a selection of Chlorophyta and Xanthophyta were detected amongst the cyanobacteria. Clusters in the diatom data correspond to salinity. Further analyses of the relationships between the biota and their environment revealed some of the strategies employed for survival. In particular, the synthesis of scytonemin was detected. This pigment is known to function as an extracellular UV sunscreen which protects cyanobacterial cells against damage by ultraviolet radiation. These results support the hypothesis that environmental extremes and biogeographical isolation control the biology of these lakes.
This overview examines available circum-Antarctic glacial history archives on land, related to developments after the Last Glacial Maximum (LGM). It considers the glacial-stratigraphic and morphologic records and also biostratigraphical information from moss banks, lake sediments and penguin rookeries, with some reference to relevant glacial marine records. It is concluded that Holocene environmental development in Antarctica differed from that in the Northern Hemisphere. The initial deglaciation of the shelf areas surrounding Antarctica took place before 10 000 14C yrs before present(BP), and was controlled by rising global sea level. This was followed by the deglaciation of some presently ice-free inner shelf and land areas between 10 000 and 8000 yr BP. Continued deglaciation occurred gradually between 8000 yr BP and 5000 yr BP. Mid-Holocene glacial readvances are recorded from various sites around Antarctica. There are strong indications of a circum-Antarctic climate warmer than today 4700–2000 yr BP. The best dated records from the Antarctic Peninsula and coastal Victoria Land suggest climatic optimums there from 4000–3000 yr BP and 3600–2600 yr BP, respectively. Thereafter Neoglacial readvances are recorded. Relatively limited glacial expansions in Antarctica during the past few hundred years correlate with the Little Ice Age in the Northern Hemisphere.
Analysis of a 1.5 m thick sediment sequence from Midge Lake, Byers Peninsula, Livingston Island, shows that the lake and its catchment have undergone significant changes during the last 4000 years. Radiocarbon dating (AMS), sediment lithology, and microfossil analyses indicate that the lake was deglaciated over 4000 14C years ago. Distinct peaks in accumulation rates of sediment, Pediastrum algae, pollen and spores, as well as changes in the diatom assemblage, suggest significant environmental changes between ca 3200 and 2700 y BP. These changes are interpreted as reflecting a milder and more humid, maritime climate. The increased humidity can explain independent observations of glacier growth during this period. The combined data also indicate that between ca 1500 and 500 y BP the area might have experienced more continental conditions with slightly colder and drier climate than today. Since the 14C dates from the Midge Lake sediments are regarded as reliable and the sediment sequence is rich in tephra layers this sediment sequence will be critical for a forthcoming tephra chronology of the region.
A floristic and taxonomic survey was made of the diatom communities of sediments and microbial mats in 66 freshwater and saline lakes and pools in the Larsemann Hills, Rauer Islands and Bølingen Islands (continental eastern Antarctica). A total of 31 taxa were distinguished, 10 of which could not be identified to species (nine) or even generic (one) level, either because they have most probably not yet been described or because they belong to species complexes that are in need of revision. Four new combinations are proposed; three species are reported for the first time from continental Antarctica, while another three are confirmed for eastern Antarctica for the first time. Analysis of literature data on Antarctic lacustrine diatoms shows that taxonomic practice has a profound influence on the assessment of distribution patterns. Force-fitting of European and North American names to Antarctic taxa and erroneous identifications have contributed to an underestimation of endemism in the diatom flora of Antarctic inland waters. In addition, changing concepts on species boundaries during the last decade influence the interpretation of biogeographic patterns. The application of a more fine grained taxonomy will almost certainly reveal a higher degree of endemism in Antarctica, and especially continental Antarctica. The present case study shows that in the Larsemann Hills Antarctic endemics account for about 40% of all freshwater and brackish taxa, while the biogeographic distribution of about 26% is unknown, mainly due to their uncertain taxonomic identity. This contradicts the view that cosmopolitanism prevails in Antarctic diatoms.
Two gravity cores, Gebra-1 and Gebra-2 from the central and eastern basins of Bransfield Strait, West Antarctica, consist mainly of hemipelagic, laminated muds with black layers rich in sand-sized volcanic ash. Micropalaeontological (diatoms and radiolarians) and geochemical (organic and inorganic) analyses, together with radiometric dating (U/Th, 14C and 210Pb) have been performed on both cores. AMS analyses on Total Organic Carbon yielded a 14C-age older than expected, 2810 yr BP for the core top of Gebra-1 and 2596 yr BP for Gebra-2. The downcore pattern of ages indicates a sedimentation rate of 130 cm kyr1 for Gebra-1 and 160 cm kyr1 for Gebra-2 210Pb anomalies suggest the core top of Gebra-1 is present-day sediment. The diatom and radiolarian assemblages are related to the sequence of neoglacial events over the last three millennia. The recent significant reduction in Chaetoceros resting spores is interpreted as a reduction in palaeoproductivity. The progressive increase in sea-ice taxa for the last three millennia may indicate a cooling trend. Greater sea-ice coverage during the coldest neoglacial events in the Bransfield Basin, as well as in the Weddell Sea and Bellingshausen Sea, is documented by increases in sea-ice taxa and reductions in Thalassiosiraantarctica/T.scotia resting spores, Fragilariopsiskerguelensis, the Lithomelissa group and the group of radiolarians. For these periods, we postulate a restricted communication between the Weddell Sea, Bellingshausen Sea and Bransfield basin. The millenial-scale changes are overprinted by a high frequency cyclicity at about 200yrs solar cycle.
Changes in the ice load since the time of the Last Glacial Maximum (LGM) contribute to the present-day vertical motion of the Antarctic continent. The obser-vation of these motions will reveal information on the ice load history. Predictions of uplift rates along a transect across the Lambert Glacier region, East Antarctica, from the coast to the southernmost rock outcrops of the Prince Charles Mountains have been computed for three deglacia-tion scenarios. The relative vertical velocities between sites on the transect are -7 to +7 mm/yr and are large enough to be detected from continuous GPS observations taken at permanent sites over several years. When available, such in-formation will discriminate between the currently available models for deglaciation of East Antarctica.
This review assesses the circumpolar occurrence of emerged marine macrofossils
and sediments from Antarctic coastal areas in relation to Late Quaternary climate changes.
Radiocarbon ages of the macrofossils, which are interpreted in view of the complexities of
the Antarctic marine radiocarbon reservoir and resolution of this dating technique, show a
bimodal distribution. The data indicate that marine species inhabited coastal environments
from at least 35 000 to 20 000 yr BP, during Marine Isotope Stage 3 when extensive ...
Limnological surveys show that fossil pigment concentration is an accurate predictor of algal production. However, experimental and mass flux studies indicate that >90% of pigment is degraded to colourless compounds before permanent burial. To reconcile these views, this paper reviews current literature on pigment degradation and proposes a hierarchical control model for pigment deposition and fossil abundance. Over the widest range of production, pigment deposition and fossil concentration are proportional to algal standing crop. However, within a narrower range, the actual concentration of pigment in sediments is regulated by photo- and chemical oxidation. Three phases of loss exist: rapid oxidation in the water column (T1/2=days); slower post-depositional loss in surface sediments (T1/2=years); and very slow loss of double bonds in deep sediments (T1/2=centuries). Despite losses during deposition, fossil and algal abundance remain correlated through time, so long as there is no change in basin morphometry, light penetration, stratification or deepwater oxygen content. At the finest scale, food-web processes can increase the preservation of pigments from edible algae by incorporating pigments into feces that sink rapidly and bypass water column losses. As a consequence of selective loss during deposition and initial burial, carotenoid relative abundance is an unreliable measure of phytoplankton community composition. Instead, absolute concentration — scaled to the historical maximum — should be used for fossil interpretations.
The Larsemann Hills are a series of rocky peninsulas and islands in Prydz Bay at 69 24 S and 76 20 E. There is about 2000 km2 of ice free land with well over 150 freshwater lakes spread evenly over the granite and gneiss hills. The nearshore islands were ice free by 9500 BP, while the present coastline was exposed by 4500 BP. A relatively steady rate of ice retreat is indicated, around 0.3 ma–1. The two freshwater lakes studied so far have evolved from oligotrophic, proglacial lagoons to fresh or brackish lakes affected by periodic influxes of salt water from sea spray and surges produced by glacial calving. The diatom assemblages increase in species diversity following marine incursion or influence. The major changes are therefore due to the postglacial recovery of sea level, rather than any intrinsic chemical evolution of the lake waters.
The water chemistry of lake systems on the edge of the Antarctic continent responds quickly to changes in the moisture balance. This is expressed as increasing salinity and decreasing lake water level during dry periods, and the opposite during wet periods. The diatom composition of the lakes also changes with these fluctuations in salinity and lake water depth. This is important, as their siliceous remains become incorporated into lake sediments and can provide long-term records of past salinity using transfer functions. In order to develop transfer functions, diatoms and water chemistry data were inter-calibrated from five different East Antarctic oases, namely the Larsemann Hills, the Blingen Islands, the Vestfold Hills, the Rauer Islands and the Windmill Islands. Results indicate that salinity is the most important environmental variable explaining the variance in the diatom flora in East Antarctic lakes. In oligo- saline lakes the variance is mainly explained by lake water depth. This dataset was used to construct a weighted averaging transfer function for salinity in order to infer historical changes in the moisture balance. This model has a jack-knifed r2 of 0.83 and a RMSEP of 0.31. The disadvantage of this transfer function is that salinity changes in oligo-saline lakes are reconstructed inaccurately due to the edge effect and due to the low species turnover along the salinity gradient at its lower end. In order to infer changes in the moisture balance in these lakes, a second transfer function using weighted averaging partial least squares (with two components) for depth was constructed. This model has a jack-knifed r2 of 0.76 and a RMSEP of 0.22. Both transfer functions can be used to infer climate driven changes in the moisture balance in lake sediment cores from oligo-, hypo-, meso- and hyper-saline lakes in East Antarctic oases between 102–75E. The transfer function for lake water depth is promising to track trends in the moisture balance of small freshwater lakes, where changes in shallow and deep-water sediments are readily reflected in changing diatom composition.
The relationship between surface sediment diatom assemblages and measured limnological variables in thirty-three coastal Antarctic lakes from the Vestfold Hills was examined by constructing a diatom-water chemistry dataset. Previous analysis of this dataset by canonical correspondence analysis revealed that salinity accounted for a significant amount of the variation in the distribution of the diatom assemblages. Weighted-averaging regression and calibration of this diatom-salinity relationship was used to establish a transfer function for the reconstruction of past lakewater salinity from fossil diatom assemblages. Weighted-averaging regression and calibration with classical deshrinking provided the best model for salinity reconstructions and this was applied to the fossil diatom assemblages from one of the saline lakes in the Vestfold Hills in order to assess its potential for palaeosalinity and palaeoclimate reconstruction.
A new Holocene sea-level record from the Vestfold Hills, Antarctica, has been obtained by dating the lacustrine–marine and marine–lacustrine transitions that occur in sediment cores from lakes which were formerly connected to the sea. From an elevation of ∼7.5 m 8000 yr ago, relative sea-level rose to a maximum ∼9 m above present sea-level 6200 yr ago. Since then, sea-level has fallen monotonically until the present. The precision of the new record makes it suitable for constraining the recent history of the ice sheet in that region, using numerical models of glacio-hydro-isostasy. Simplified regional models suggest that the ice-sheet margin has retreated 30–40 km since the last glacial maximum, with 600–700 m of thinning occurring at the present coastline.
Stratigraphically constrained cluster analysis is a multivariate method for quantitative definition of stratigraphic zones. As opposed to ordinary, unconstrained cluster analysis, only stratigraphically adjacent clusters are considered for merging. The method of incremental sum of squares has been used widely for unconstrained analyses and has proved particularly satisfactory for pollen frequency data. CONISS is a FORTRAN 77 program for stratigraphically constrained cluster analysis by this method. Several data transformations lead to different implicit dissimilarity coefficients. As an option, the program also will perform an unconstrained analysis, which can be useful for comparison with the constrained analysis.
The biomass and percentage cover of subtidal macro algae were recorded at five sites near Anvers Island, along the Antarctic Peninsula (64°S, 64°W) in 1989. Total macroalgal wet biomass ranged from 1.64 to 6.34 kg m−2. The largest biomass contributors were the large overstory brown algae (Phaeophyceae) Desmarestia antarctica Moe et Silva, Desmarestia menziesii J. Agardh, Desmarestia anceps Montagne and Himantothallus grandifolius (Skottsberg) Zinova. These species had an overall cover of 72% of the bottom. D. menziesii and/or D. anceps were dominant at 2 and 5 m. D. antarctica dominated the overstory at 10 and 15 m. H. grandifolius was also abundant at 15 m and dominated at 20 m. Several red macroalgae (Rhodophyta) were also conspicuous: Iridaea cordata (Turner) Bory and Curdiea racovitzae Hariot at 2 and 5 m; Myriogramme mangini (Gain) Skottsberg and Plocamium cartilagineum (Linnaeus) Dixon at 10 and 15 m; and Gigartina skottsbergii Setchell et Gardner and Sarcodia montagneana (Hooker et Harvey)...
Four diatom assemblages are identified from the surface sediments of Prydz Bay and the Mac.Robertson Shelf using multivariate analysis. A coastal assemblage is characterised by the sea-ice diatoms Fragilariopsis curta, F. angulata, F. cylindrus and Pseudonitzschia turgiduloides. A continental shelf assemblage is characterised by sea-ice and ice-edge diatoms, and an oceanic assemblage is characterised by the open-water diatoms Fragilariopsis kerguelensis, Thalassiosira lentiginosa, T. gracilis var. expecta and Trichotoxin reinboldii. The Cape Darnley assemblage contains both sea-ice and open-water diatoms, but all are characteristically large and heavily silicified. Multiple regression has been used to identify the relationships between the diatom assemblages and known environmental variables. There are strong correlations between the coastal, shelf and oceanic assemblages and ecological conditions, including latitude, sea-ice distribution and ocean currents. The Cape Darnley assemblage is thought to represent an assemblage from which the smaller and more lightly silicified species have been removed by current winnowing.
The Age Calibration Program, CALIB, published in 1986 and amended in 1987 is here amended anew. The program is available on a floppy disk in this publication. The new calibration data set covers nearly 22 000 Cal yr (approx 18 400 14C yr) and represents a 6 yr timescale calibration effort by several laboratories. The data are described and the program outlined. -K.Clayton
A modified ignition loss method is described for determining organic and carbonate carbon in calcareous sedimentary materials using equipment found in most laboratories. The method has been found to equal or excel the accuracy and precision of other methods tested and has the advantage of being considerably faster if large numbers of samples are to be analyzed.
Downcore diatom data from a deep basin in Granite Harbor, Antarctica, provide new, high-resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years. The influence of global-scale climatic change, during the time of the Medieval Warm Period and possibly the Little Ice Age, is revealed by long-term changes in floral assemblages, as recorded by changes in the relative concentration of Nitzschia cylindrus. The diatom data suggest that Granite Harbor experienced less annual ice and pack ice cover during both these periods, possibly because of higher temperatures during the Medieval Warm Period and stronger offshore winds during the Little Ice Age. The sedimentary record reveals several distinct, short-lived events, in which nearly monospecific blooms of Corethron criophilum and Chaetoceros spp. occurred, possibly the result of strong stabilization of the upper water column and were most likely a response to regional, rather than global conditions. Although short-lived, these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor.
Lake Sonachi, Kenya, is a small alkaline-saline crater lake that over the past 175 years has experienced considerable fluctuations in lake depth ( Zmax 5 3-18 m) and an alternation of meromictic and holomictic episodes lasting from a few years to several decades. Paleolimnological methods were used to reconstruct the long-term dynamics of algal and invertebrate communities in Lake Sonachi in relation to the historical evolution of their physical and chemical environ- ment. Multivariate statistical analysis revealed only weak correlation between the stratigraphic distributions of fossil algal pigments, diatoms, and chironomid larvae in 210 Pb-dated sediment cores and the documented or reconstructed variation in lake depth, mixing regime, and surface-water conductivity. The eventful biological history of Lake Sonachi exemplifies the complexity of long-term community dynamics in tropical African soda lakes and reveals how phytoplankton com- munity structure can exert direct control on benthic and planktonic invertebrate communities. The modest phytoplankton abundance and photosynthetic activity of Lake Sonachi when compared with other tropical African soda lakes represent recent lake conditions, resulting from a dramatic decline of filamentous cyanobacteria (e.g., Spirulina platensis) between the 1930s and 1970s and incomplete replacement by the small coccoid cyanobacteria (e.g., Synechococcus bacillaris), which are dominant today. This reduction in algal biomass favored benthic and planktonic invertebrates by reducing the prevalence of complete water-column anoxia associated with intense nighttime respiration of cyanobacterial blooms. Anoxia-intolerant halobiont chironomids expanded during an episode of low lake level (Zmax , 4 m), holomixis, and high conductivity (.9,000 m Sc m 21 ) in the late 1940s and 1950s, whereas they had failed to do so under similar conditions in the late 19th century when algal abundance was high. Planktonic cladocerans developed high population densities only during two short meromictic phases in the 1970s when conductivity was modest (3,000-6,000 m Sc m 21 ) and algal abundance was low. The decline of filamentous cyanobacteria also increased water-column transparency but apparently did not increase benthic diatom abundance.
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Statistical analyses of diatom assemblages from radiocarbon-dated sediment cores were used to reconstruct changing palaeoceanographic conditions in the western and west-central Ross Sea, Antarctica, from. c.12 14C kyr BP to the present. Data from three Kasten cores support a north-to-south time-transgressive glacial/interglacial transition. Assemblages at the base of each core suggest that glacial processes affecting frustule preservation were significant during the late Pleistocene. Increasing biogenic silic and decreasing per centages of reworked species suggest that upper water-column productivity, instead of preservational processes, increasingly dominates diatom assemblages during grounding-line recession (c.12to c.6 14C kyr BP). A warm ing during the middle to late Holocene (c.6to c.3 14C kyr BP) may have resulted in: (a) spring sea ice melting prior to the annual inception of the Ross Sea polynya in the west-central Ross Sea, and (b) increased plateletice delivery due to increased melting beneath the ice sheet in coastal areas. An increasingly cooler late Holocene (c.3 14C kyr BP to the present) may have resulted in: (a) decreased sea-ice melting prior to physical disinte gration of the annual sea-ice cover by spring inception of Ross-Sea-polynya winds in the west-central Ross Sea, and (b) decreased platelet-ice delivery in coastal areas.
Fifty four surface sediment samples from the western and central Ross Sea were examined to determine relationships between modern oceanographic conditions and surface sediment diatom assemblages. A centered R mode principal components analysis demonstrates four geographically distinct assemblages. The assemblage just north of the Ross Ice Shelf in the central Ross Sea is most closely associated with Stephanopyxis spp. (a heavily silicified diatom abundant during the Pliocene), and may result from a combination of winnowing/reworking, and modern flux of primarily non-siliceous algae. The algal assemblage in the western part of the central Ross Sea is most closely associated with Thalassiosiragracilis (an open water diatom), and reflects early seasonal pack ice break up during the late spring inception of the Ross Sea polynya. The algal assemblage north of Drygalski Ice Tongue, in the western Ross Sea, is most closely associated with Fragilariopsiscurta (a diatom common in stratified ice edge zones), suggesting that water column seeding by species melting out of coastal sea ice is important in this area. The assemblage south of Drygalski Ice Tongue is most closely associated with resting spores of Thalassiosiraantarctica (a diatom associated with coastal waters). Although the habitat of T.antarctica requires future research, we speculate that sea ice conditions unique to area B support an autumnal T.antarctica bloom.
The retreat of five small Antarctic Peninsula ice shelves in the late 20th century has been related to regional (possibly anthropogenic) climate warming. We use the record of ice- rafted debris (IRD) in cores to show that the Prince Gustav Channel ice shelf also retreated in mid-Holocene time. Early and late Holocene-age sediments contain IRD derived entirely from local ice drainage basins, which fed the section of ice shelf covering each site. Core- top and mid-Holocene (5 2 ka) sediments include a wider variety of rock types, recording the drift of far-traveled icebergs, which implies seasonally open water at the sites. The period when the Prince Gustav ice shelf was absent corresponds to regional climate warming deduced from other paleoenvironmental records. We infer that the recent decay cannot be viewed as an unequivocal indicator of anthropogenic climate perturbation.
The Holocene sea-level high stand or tt" marine limittt" in Wilkes Land, East Antarctica, reached ~ 30 m above present sea level at a few dispersed sites. The most detailed marine limit data have been recorded for the Windmill Islands and Budd Coast at the margin of the Law Dome ice cap, a dome of the East Antarctic Ice Sheet (EAIS). Relative sea-level lowering of 30 m and the associated emergence of the Windmill Islands have occurred since 6900 14C (corr.) yr B.P. Numerical modeling of the Earth's rheology is used to determine the glacio-isostatic component of the observed relative sea-level lowering. Glaciological evidence suggests that most of EAIS thickening occurred around its margin, with expansion onto the continental shelf. Consequently, a regional ice history for the last glacial maximum (LGM) was applied in the glacio-isostatic modeling to test whether the observed relative sea-level lowering was primarily produced by regional ice-sheet changes. The results of the modeling indicate that the postglacial (13,000 to 8000 14C yr B.P) removal of an ice load of between 770 and 1000 m from around the margin of the Law Dome and adjacent EAIS have produced the observed relative sea-level lowering. Such an additional ice load would have been associated with a 40- to 65-km expansion of the Law Dome to near the continental shelf break, together with a few hundred meters of ice thickening on the adjoining coastal slope of the EAIS up to 2000 m elevation. Whereas the observed changes in relative sea level are shown to be strongly influenced by regional ice sheet changes, the glacio-isostatic response at the Windmill Islands results from a combination of regional and, to a lesser extent, Antarctic-wide effects. The correspondence between the Holocene relative sea-level lowering interpreted at the margin of the Law Dome and the lowering interpreted along the remainder of the Wilkes Land and Oates Land coasts (105$[$deg$]$-160$[$deg$]$ E) suggests that a similar ice load of up to 1000 m existed along the EAIS margin between Wilkes Land and Oates Land.
The major influences on the salinity and water level of an Antarctic lake are parameterized and a palaeohydrological model linking the palaeosalinity of an Antarctic lake to the palaeohydrology of the lake is developed. Climatic change in this lake is recorded in the evaporative loss trend reconstructed from water level and lakewater salinity estimates. A decrease in salinity betweeñ700 and 200 years BP corresponds with c. 5 m increase in water level over the same time period. Both water level and lakewater salinity then stabilize in the last ~200 years BP. The palaeohydrological model derived from the changes inferred in salinity and water level shows that there is no significant change in evaporation for the last ~700 years but that a lower evaporation period is evident at ~150–200 years BP suggestive of a mild ‘Little Ice Age’ event in the Vestfold Hills.
Solidified stomach oil deposits in snow petrel colonies in the Antarctic proved to be suitable for 14C dating and provide important palaeobiogeographical and palaeoenvironmental information. Following earlier studies in the Untersee oasis (Central Dronning Maud Land) we present here 14C measurements on comparable deposits from the Bunger Hills (66°10′S, 101°E). The conventional 14C age of the basal layer reflects the occupation age of any particular nesting site and therefore a minimum age for the time when this area became ice-free. According to the 14C results the occupation of the southern part of the Bunger Hills by petrels started about 10000yr ago. The breeding colonies expanded continuously following local ice retreat. The most intensive phases of colonization seem to have been from 8–6 kyr BP and during the past 2 kyr.
The postglacial sea-level history along a cross-section of western Norway has been studied in detail. Ten local sea-level curves were used to construct an equidistant shoreline diagram, covering the last 13000 years. This includes 76 radiocarbon dates, of which the majority represent lacustrine sediments at the marine/lacustrine boundary in cores from emerged lakes. The distance between the westernmost and easternmost sites is 170 km and the difference in total emergence along this profile is more than 200 m. The shorelines all dip westward with a decreasing gradient through time. The Late Weichselian lines are all slightly curved whereas the Holocene lines are apparently straight. After the formation of the uppermost shoreline by around 12 800 BP there was a rapid emergence that decelerated with time to a near standstill during the Younger Dryas. From about 10 300 there was again a rapid emergence followed by the Tapes transgression along the coast and a standstill in the most easterly areas. At the western end of this profile, the Tapes transgression started around 9000 and culminated approximately 6000 BP, when a gradual regression occurred. To the east the early Holocene regression minimum occurs at a younger date and the transgression maximum is up to 1500 years older.
Lake Fidler is an ectogenic meromictic lake with a monimolimnion maintained by periodic incursions of brackish water from the lower Gordon River estuary. A dam across the middle reaches of the Gordon River has restricted these incursions of brackish water and meromictic stability has rapidly declined. A palaeolimnological study was carried in order to assess the historical development of meromixis and the impact of the dam on the microbiological communities in the lake. Fossil pigments in a 17 m sediment core were analysed using reverse phase high performance liquid chromatography (rp-HPLC) and mass spectrometry (MS). In addition, taphonomic studies of pigment production, deposition and degradation in the water column and surface sediments were used to identify planktonic and benthic pigment degradation processes and constrain the stratigraphic interpretation. Results comparing the pigment composition of pelagic sediment traps and littoral surface sediments indicated that the core from the centre of the lake would permit a historical reconstruction of planktonic bacterial and algal communities. Marked increases in prokaryotic pigments ca 3500 yr B.P. suggested the possible colonisation of a chemocline by phototrophic bacteria. Further changes in chlorophyll: carotenoid ratios and changes in relative abundances of both chlorophyll a and bacteriochlorophyll c derivatives also indicated that a change in the depositional environment had occurred; possibly due to altered stratification or anoxia. From this we infer the onset of either intermittent or permanent meromixis. Further increases in prokaryotic pigment abundance suggested that the present state of permanent meromixis was firmly established by 2070 50 14C yr B.P., and diatom analysis confirmed the development of a stable mixolimnion. High resolution studies of the top 10 cm of sediments measured pigments in mean concentrations of 15.1 ng g-1 with a mean S.D. of only 2.78 indicating little change in pigment abundance since the construction of the dam. Thus, Lake Fidler still retains most of the features of meromixis. However, evidence from nearby Lake Morrison and Sulphide Pool has shown that any further declines in meromictic stability will cause a rapid reversion to holomixis. Palaeolimnological evidence from the early stages of meromictic development of Lake Fidler suggests that such reversion to holomixis may not permanently eliminate all the microbiological communities, and that, given time, they may return and prosper with re-establishment of a suitable chemocline. These studies will guide recommendations for a management strategy to prevent the further decay of meromixis in the Gordon River lakes.
Accurate identification of fossil pigments is essential if they are to be used as biomarker compounds in palaeolimnological studies. In recent years High Performance Liquid Chromatography (HPLC) has greatly enhanced the efficiency with which fossil pigments can be characterised and quantified. Using HPLC, undegraded pigments are typically identified through retention times, absorbance spectra and co-chromatography with authentic reference standards. However, lake sediments may also contain degraded pigments for which there are often no standards, and which may be difficult to identify using HPLC alone. In this study, we submitted HPLC fractions of fossil pigments and pigment derivatives collected from a meromictic lake in south west Tasmania, to a combination of Mass Spectrometry (MS) techniques including Electron Impact (EI) and static Liquid Secondary Ion MS (LSIMS) to identify their molecular ion characteristics and organic chemical composition. Mass Spectrometry permitted the detection of specific mass ions which were used to verify the identity of pigments and their derivatives. These included five carotenoids, chlorophyll a and derivatives, three previously described bacteriochlorophyll c derivatives with molecular weights of 770, 784, and 802, and two undescribed derivatives of bacteriochlorophyll c with molecular weights of 766 and 788. With these improved identifications we speculate on the pathways and modes of pigment degradation in the lake and asses the value of the degraded pigments as biomarkers. The use of MS permitted the identification of a greater number of signature pigments of algal and bacterial communities thus increasing the palaeolimnological value of the sediments. These methods are best applied in fossil pigment studies where there are a large number of unknown pigments and pigment degradation products, and where there are no authentic standards for co-chromatography. Practical suggestions for pigment MS are included in the discussion.
A procedure is described for making diatom microscopy slides from large numbers of sediment samples, simultaneously. The method uses small sediment samples, small test tubes, small amounts of hydrogen peroxide, no decantings, no centrifuging, and it requires no washing-up of glassware. It is, therefore, fast, cheap, gentle to the diatoms and needs little fume cupboard space.
The hitherto longest found lake sediment sequence on Byers Peninsula, Livingston Island, South Shetland Islands, was analysed with respect to lithology, chronology, diatoms, Pediastrum, pollen and spores, mosses, mineralogy, and sediment chemistry. During the ca. 5000 year long development the sediments were influenced by frequent tephra fall-outs. This volcanic impact played a major role in the lake's history during two periods, 4700–4600 and 2800–2500 BP, but was of importance during the lake's entire history with considerable influence on many of the palaeoenvironmentally significant indicators. The large and complex data set was analysed and zonated with different types of multivariate analysis. This resulted in a subdivision of the sequence into 8 time periods and 21 variables. Redundancy analysis (RDA) of this data set, both without and with the tephra periods, and with 4–6 of the variables as explanatory environmental variables, reveal that climatic/environmental signals are detectable. The palaeoclimatic picture that emerged out of the tephra noise suggests that the first 100 years were characterized by mild, humid conditions. This was followed by a less mild and humid climate until ca. 4000 BP when a gradual warming seems to have started, coupled with increased humidity. These mild and humid conditions seem to have reached an optimum slightly after 3000 BP. At ca. 2500 BP a distinct climatic deterioration occurred with colder and drier conditions and long seasons with ice cover. This arid, cold phase probably reached its optimum conditions at ca. 1500 BP, when slightly warmer conditions might have prevailed for a while. Except for the modern sample with rather mild climate, the last 1400 years seem to have been fairly arid and cold, and the effects of the frequent volcanic activity during this period is only vaguely seen in the records.
Watts Lake is a 0.38 km2 freshwater lake in the Vestfold Hills, East Antarctica (68°35′S 78°00′E) that was formerly a marine embayment. The water level of the lake is currently rising, it is now at −5.8 m altitude. The lake currently has a maximum salinity of 2.4 g 1−1 and no outlet. Abundant Holocene marine fossil molluscs, polychaetes and algae dated at 4700–8000 14C yr B.P. indicate that the lake was one basin of a complex marine inlet during the early to mid Holocene. A prominent terrace formed in the tide zone during this period. Processes involved in terrace formation are discussed using Watts Lake as an example. Other basins of this inlet have now become saline or hypersaline. Isostatic uplift isolated the whole inlet from the sea and allowed the basins to become separate lakes. From 3000–4000 14C yr B.P. copious volumes of freshwater from nearby stagnant ice and possibly from a major river system poured into Watts Lake displacing the salt water over a sill at the eastern end. Within 2000 yr the lake was fresh. Freshwater inflow declined and the lake level began to fall from evaporation. Cyanobacterial stromatolites formed from 2800 to 1700 14C yr B.P. at the eastern end of the lake. At least two other lakes in the Hills have similar histories.
Holocene, marine deposition in Lallemand Fjord, Antarctic Peninsula, is reinterpreted using statistical analyses (cluster analysis, analysis of variance, nonmetric multidimensional scaling and multiple regression) to compare diatom assemblages and the primary sedimentological proxies. The assemblages have been deposited in a variable sea ice zone over the last ca. 10,500 yr BP in response to a climate change. In the Late Pleistocene/early Holocene (10,580–7890 yr BP), a sea ice diatom assemblage was deposited in the presence of a retreating ice shelf at the head of the fjord. In the mid Holocene (7890–3850 yr BP), an open water assemblage was deposited and sea ice cover was at a minimum. We associate the assemblage with climatic warming, which characterizes much of the Antarctic Peninsula during this time. A second sea ice assemblage, different from that deposited in the early Holocene, has been deposited in Lallemand Fjord since the late Holocene (<3850 yr BP). The assemblage reflects Neoglacial cooling, an increase in sea ice extent and/or an advance of the Müller Ice Shelf.
A study of 230 surface sediment samples collected in the Atlantic sector of the Southern Ocean between the southernmost Weddell Sea and the Subtropical Zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance. Estimations of diatom valves per gram dry sediment display numbers of (50–200) × 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the Polar Front and maximum values of greater than 200 × 106 in the near-shore sedimentary basins off the Antarctic Peninsula. Lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the Weddell Basin. Despite alteration of the diatom assemblages prior to their incorporation into the sediment record, the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography (water temperature). These relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record. Another close link occurs between the distribution of sea ice and sea ice related diatoms.
Microfaunal and microfloral data from two gravity cores, and stable-isotope results from one of these cores taken on Fram Bank near Prydz Bay, Antarctica indicate changes in sea-ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr. Modern diatom assemblages indicative of ice free conditions 1–2 months of the year, and dominated by Nitzschia species became prevalent some time around 2000–2700 yr B.P. The occurrence of Chaetoceros spp. diatom spore-dominated assemblages, and increased abundances of benthic and planktonic foraminifera, ostracods, and diatoms, coupled with carbon- and oxygen-isotope changes around 2700–3400 yr B.P. strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period. Based on diatom assemblage associations recognized in modern environments, the upper water column of Fram Bank shelf waters was probably stratified during that time due to the presence of low-salinity melt water and a very shallow mixed layer, protected from storms, with sea-ice cover for less than 10 months per year. The close correspondence of δ¹³C and δ¹⁸O values from N. pachyderma (r² = 0.74) throughout one core suggests that whatever oceanographic conditions influenced δ¹⁸O also influenced δ¹³C. Changes in Prydz Bay microfossil abundances and isotopes may result from alterations in circulation patterns, upwelling conditions, or sea-ice patterns which significantly affected benthic and planktonic productivity in the area.
Comparison of diatom data from modern surface sediments in Prydz Bay and the Kerguelen Plateau with diatom assemblages from the Sørsdal Formation, Vestfold Hills, indicates that the climate was warmer than present during the early Pliocene (4.5–4.1 Ma). Extant, sea-ice associated diatoms are significantly less abundant throughout the Sørsdal Formation than in the modern Antarctic coastal zone. Extant diatoms in the Sørsdal Formation, including Stellarima stellaris, Thalassiosira oliverana, Fragilariopsis sublinearis, Pseudo-nitzschia turgiduloides and Eucampia antarctica var. recta, are consistent with annual sea-surface temperatures (SST) of between −1.8 and 5.0°C. The presence of S. stellaris indicates that the summer SSTs were >3°C during some intervals. The absence of calcareous coccoliths and the silicoflagellate Dictyocha suggests that the upper limit for summer SST was <5°C. These data indicate that early Pliocene summer SST were between 1.6 and 3°C warmer than today. Abundant Chaetoceros cysts infer that stratified, open-water conditions were present during summer/spring. Ice sheet models suggest that warming of the magnitude evident in the Sørsdal Formation (≤3°C) should have resulted initially in increased snow accumulation and ice sheet growth. However, ice sheet growth was probably short-lived, as the long-term response to this warming in the early Pliocene resulted in a significant decrease in ice volume and deposition of the Sørsdal Formation. Other factors, such as increased basal-ice sliding and higher discharge (icebergs and melt-water), probably led to significantly elevated ablation rates from the Pliocene ice sheet, resulting in ice sheet retreat.
Sediment profiles from several lakes/ponds in the northern, ice-free area of James Ross Island, Antarctica, were the subject of a multi-disciplinary palaeoenvironmental investigation. The results, obtained from lithological, geomagnetic, geochemical and diatom analyses, and the frequency of Branchinecta eggs, were evaluated with multivariate statistics and provide a fairly detailed picture of climate change during the last 5000 years. New radiocarbon dates are combined with previously published 14C dates, so as to date the palaeoenvironmental and palaeohydrological changes identified by the stratigraphic studies. In combination with the findings of glacial geological studies our data suggest that the Brandy Bay glacier began to recede rapidly just before 5000 yr B.P., due to calving and moisture starvation caused by cold and arid conditions. In one of the ponds studied gypsum began to precipitate as a consequence of these conditions when the influence of glacial meltwater ceased. This hypothesis was tested by hydrochemical modeling. At approximately 4200 yr B.P. the climate became more humid (and warmer) and the pond supported a fairly diverse biota, which included a variety of diatom species and, for example, Branchinecta gaini, a crustacean that feeds on benthic cyanobacterial mats. The Brandy Bay glacier probably advanced during this humid period, but the advance was interrupted by subsequent arid conditions which started at 3000 yr B.P. During this arid phase, glaciers became completely absent from the study area. As a result formerly large lakes, fed by glacial meltwater, transformed into small, enclosed, brackish water bodies that contained B. gaini. The arid and fairly cold conditions lasted for 1500–2000 years, until approximately 1200 yr B.P. when the aquatic systems expanded and their salinity was lowered as a result of increased snow accumulation and glacial expansion. The increased deposition of minerogenic matter caused by glacial erosion and meltwater inflow probably caused the disappearance of Branchinecta on James Ross Island. We regard this most recent phase as a period of increased humidity and warmth compared to the previous period, although the conditions appear to be less warm and humid than those which prevailed during the climatic optimum between 4200 and 3000 yr B.P. In spite of certain correlation problems we tentatively correlate our results to other studies of Holocene environments in Antarctica, and from that it can be suggested that the climatic optimum was of circumpolar significance. Therefore the climatic oscillations recorded in sediments on James Ross Island may reflect oscillations in the anticyclonic stormtracks and the strength of the high pressure cell over the inland ice sheet.
A comparison is made of the Holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east Antarctica (Vostok, Dome B, Plateau Remote, Komsomolskaia, Dome C, Taylor Dome, Dominion Range, D47, KM105, and Law Dome) and west Antarctica (Byrd), with temporal resolution from 20 to 50 yr. The long-term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations. All the records confirm the widespread Antarctic early Holocene optimum between 11,500 and 9000 yr; in the Ross Sea sector, a secondary optimum is identified between 7000 and 5000 yr, whereas all eastern Antarctic sites show a late optimum between 6000 and 3000 yr. Superimposed on the long time trend, all the records exhibit 9 aperiodic millennial-scale oscillations. Climatic optima show a reduced pacing between warm events (typically 800 yr), whereas cooler periods are associated with less-frequent warm events (pacing >1200 yr).
New experiments were performed with three-dimensional thermomechanical models of the Greenland and Antarctic ice sheets to simulate their behaviour during the glacial cycles, to reconstruct their thickness and extent at the Last Glacial Maximum (LGM), and to estimate their glacio-eustatic contribution to the global sea-level stand. The calculations used improved ice-dynamic and isostatic treatments, updated datasets on higher grid resolutions, and refined climatic treatments based on newly calibrated transfer functions between ice core records and climatic perturbations. Results are discussed from a reference run with standard parameters that is compared with available glacial-geological observations, and from a series of sensitivity experiments focusing on isostatic adjustment, thermomechanical coupling, climatic forcing, mass-balance changes, and basal melting rates and viscosity changes of Antarctic ice shelves. For the Antarctic ice sheet, we find that volume changes are closely linked with grounding line changes of the West Antarctic ice sheet. At the LGM, the grounding line extended close to the continental shelf break almost everywhere. Ice over central East Antarctica was generally thinner than today and varied mainly in accordance with accumulation fluctuations. For the Greenland ice sheet, melting is important only during interglacial periods and the most sensitive period concerns the size of the ice sheet during the Eemian. At the LGM, the Greenland ice sheet extended beyond the present coastline to cover at least the inner continental shelf and thinned by up to several hundred meters in central areas. For a plausible range of parameters, the experiments indicate that at the time of maximum sea-level depression (21 kyr BP), the Antarctic ice sheet contributed 14–18 m to the sea-level lowering, and the Greenland ice sheet 2–3 m, significantly less than the older CLIMAP reconstructions. Whereas both ice sheets were at 21 kyr BP close to their maximum extent, the experiments also indicate that their maximum volumes were reached only by 16.5 kyr BP (Greenland) and 10 kyr BP (Antarctica), equal to an additional sea-level lowering of, respectively, 0.4 and 3.7 m. Holocene retreat was essentially complete by 5 kyr BP in Greenland, but is found to still continue today in West Antarctica before reversing to growth during the next millenium. The models were found to reproduce gross features of the ice sheet's history since the LGM in reasonably good agreement with available glacial-geological data, although observational control on ice thickness changes remains very limited.