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Comparison of diatom preservation between oxic and anoxic basins in ellis fjord, antarctica
Abstract
Sedimentary diatom assemblages from adjacent sub-basins in Ellis Fjord reflect the differing degree of oxygenation in each of their bottom waters. The absence of a benthic fauna and a lower pH in the anoxic sub-basin allows the preservation of the smaller, more fragile diatoms. By contrast, the presence of an active benthos and a higher pH in the well-oxygenated sub-basin results in preservation of only the more robust species. Approximately 50% of diatom cells sedimenting from the surface waters of the oxygenated sub-basin of Ellis Fjord are removed prior to incorporation into the sediments.
... Chaero-ceros spp., Entomeneis kjellmanii Cleve, Nitzschia cloisterium (Ehrenberg) W. Smith N. stellata Mangin and N. subcurvata Hasle) by the above authors are not preserved in abundance in sediments. The lightly silicified and fragile frustules of such species are have been lost to the sediment by mechanical breakage and selective dissolution (McMinn, 1995). Coupled with bioturbation and selective predation, these processes alter the original diatom assemblage, leading to a decline in both species diversity and abundance (Mikkelsen, 1980;Dunbar et al., 1989;McMinn, 1995). ...
... The lightly silicified and fragile frustules of such species are have been lost to the sediment by mechanical breakage and selective dissolution (McMinn, 1995). Coupled with bioturbation and selective predation, these processes alter the original diatom assemblage, leading to a decline in both species diversity and abundance (Mikkelsen, 1980;Dunbar et al., 1989;McMinn, 1995). Although F: qlindrus is small and lightly silicihed, its high abundance in the water column and ice communities is reflected in the sediment. ...
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.
... Fecal pellets and coprolites of the Cretaceous age were described to contain diatoms (Chin et al., 2008), hence, analysis of Mesozoic coprolites may contain undiscovered fossil communities. Previous studies suggest that diatom preservation is elevated under anoxic conditions (McMinn, 1995). Soft tissues of invertebrates buried under anoxic conditions were found in sediments as old as 380 Ma (Melendez et al., 2013). ...
Paleontological observations of ancient flora and fauna provide powerful insights into past diversity and relationship dynamics between organisms and their environments. Diatoms are globally distributed protists that influence major biogeochemical cycles and sustain oceanic food webs. The fossil diatom record extends 120 million years back to the Early Cretaceous where rare deposits were discovered worldwide and are occasionally represented by diverse communities. However scarce, the taxonomic richness and geographical spread of these diatom communities suggest prior evolutionary events and therefore earlier deposits. To complement the existing fossil information and to discover diatom deposits predating 120 Ma, we examined 33 study sites from cores and outcrops across oceans and continents. These efforts did not generate new fossil discoveries, however. Our assessment suggests biogenic silica that comprises the cell wall of diatoms was likely dissolved from Mesozoic sediments through diagenetic processes. Altogether, the search for the oldest diatoms must continue but should target sediments that experienced shallow burial and concretions.
... Among the identified phytoplankton species at P01, there were relatively high cell densities of Fragilariopsis doliolus (0.8 × 10 3 cell L −1 ) and Asterionella glacialis (0.4 × 10 3 cell L −1 ). Both of them have been reported to be distributed mainly in cold-waters, such as the Antarctic Ocean (Hasle & Syvertsen, 1997) and the North Atlantic Ocean (McMinn, 1995). Their cold-adaptation might support higher isoprene production at lower temperatures, thereby leading to a significant deviation of the biological isoprene production rate (Chl-a-normalized) at P01 compared to the other stations when plotted against SST. ...
Marine isoprene plays a crucial role in the formation of secondary organic aerosol within the remote marine boundary layer. Due to scarce field measurements of oceanic isoprene and limited laboratory‐based studies of isoprene production, assessing the importance of marine isoprene on atmospheric chemistry and climate is challenging. Calculating in‐field isoprene production rates is a crucial step to predict marine isoprene concentrations and the subsequent emissions to the atmosphere. The distribution, sources, and dominant environmental factors of isoprene were determined in the Northwest Pacific Ocean in 2019. The nutrient enrichment in the Kuroshio Oyashio Extension (KOE) surface seawater, driven by the upwelling and atmospheric deposition, promoted the growth of phytoplankton and elevated the isoprene concentration. This was confirmed by observed responses of isoprene to nutrients and aerosol dust additions in a ship‐based incubation experiment, where the isoprene concentrations increased by 70% (t = 4.417, p < 0.001) and 35% (t = 2.387, p < 0.05), respectively. Biogenic isoprene production rates in the deck incubation experiments were positively related to chlorophyll a, temperature, and solar radiation, with an average production of 7.33 ± 4.27 pmol L⁻¹ day⁻¹. Photochemical degradation of dissolved organic matter was likely an abiotic source of isoprene, contributing to approximately 14% of the total production. Driven by high isoprene production and extreme physical disturbance, the KOE showed very high emissions of isoprene of 46.0 ± 13.0 nmol m⁻² day⁻¹, which led to a significant influence on the oxidative capacity of the local atmosphere.
... This may be explained, firstly, by a considerably higher content of silica in the frustule (in comparison with species of pennate diatoms) and, secondly, by their autecology: since they are planktonic, they participate less in near-bottom taphonomic processes. We believe that the interesting fact is dissolution of diatom frustules developed in the water MOSCOW body with supposed low pH, while, on the contrary, the diatom frustules dissolve at high pH according to literature [15][16][17]. Evidently, this issue requires further investigation. With consideration of the obtained data, we cannot relate preservation level to a certain environmental factor. ...
Results of a study of diatoms from Holocene peatbog sediments from Shemya Island (Aleutian Islands, United States) are presented. The column of peat sediments (385 cm depth) was investigated (formation of peat sediments began more than 9500 years ago). Sixty-seven taxa of 31 genera, 17 families, eight orders, and three classes were identified. According to results of taxonomical and eco-geographical analyses, most taxa belong to the order Naviculales and family Pinnulariaceae and are benthic organisms with cosmopolitan distribution. Forms with different quality of frustule preservation were revealed. Centric diatoms demonstrate the best preservation in sediment. Of special interest is the dissolution of frustules in a water body with presumably low pH value. Dynamics of the pattern of species relative abundance was studied. Several zones with characteristic diatom complexes are distinguished. Analysis of distribution of diatoms in the column showed that, apparently, this locality was a shallow oligotrophic reservoir with a relatively low pH in the past. Water level changed occasionally, but trophic level did not change over the period of the reservoir’s existence.
... lineola (Fig. 3). Despite the fact that these species are often important contributors to the living diatom assemblages in the surface layer in the AZ, they are most likely overrepresented in the sediment traps due to selective dissolution in the upper water column and mechanical breakage by zooplankton of weakly silicified species that can cause profound modifications in the original diatom assemblage (McMinn, 1995;Jordan and Stickley, 2010;Rigual-Hernández et al., 2016). The variations in the composition of the diatom sinking assemblages across the stations seem to be largely determined by the influence of sea ice cover, a critical factor determining the distribution of diatom assemblages in the modern sediments of the Southern Ocean (Zielinski and Gersonde, 1997;Armand et al., 2005). ...
The Antarctic Zone, the southernmost belt of the Antarctic Circumpolar Current, plays an important role in the control of atmospheric carbon dioxide concentrations. In the last decade, a number of studies have highlighted the importance of diatom assemblage composition in influencing the magnitude of the organic carbon and biogenic silica fluxes exported out of the mixed layer in Southern Ocean ecosystems. Here we investigate the relationship between the makeup of the diatom assemblage, organic carbon and biogenic silica export and several significant environmental parameters using sediment trap records deployed in different sectors of the Antarctic Zone. The study is divided in two parts. We first present unpublished diatom species flux data collected by a sediment trap in the offshore waters of Prydz Bay (Station PZB-1) over a year. The results of this study revealed a major export peak of diatom valves in Austral summer and two small unexpected secondary flux pulses during full winter conditions. The summer diatom sinking assemblages were largely composed of small and rapidly dividing species such as Fragilariopsis cylindrus, Fragilariopsis curta and Pseudo-nitzschia lineola, while winter assemblages were dominated by Fragilariopsis kerguelensis most reflecting its persistent strategy and selective preservation. In the second part of the study, we compare the annual diatom assemblage composition and biogeochemical fluxes of Station PZB-1 with flux data documented in previous sediment trap studies conducted in other sectors of the Antarctic Zone in order to investigate how diatom floristics influence the composition and magnitude of particle fluxes in the Antarctic Zone. The lack of correlation between the annual diatom valve, organic carbon and biogenic silica fluxes across stations indicates that other factors aside from diatom abundance play a major role in the carbon and silica export in AZ. Among these factors, the composition of the diatom assemblage appears to be critical, as suggested by the strong and significant correlation between Bio-SiO2 and the valve fluxes of F. kerguelensis alone, that this species is the main Bio-SiO2 vector from the surface layer to the deep ocean in the AZ waters, regardless of its relative abundance. Lastly, the good correlation between the annual fluxes of the group of small Fragilariopsis species with satellite-derived chlorophyll-a concentration estimates over the study stations, suggest that high abundances of these species in the Southern Ocean paleorecords could be used as a proxy of high algal biomass accumulation.
... The rising absolute and relative abundance since the 1950s of Pseudo-nitzschia , a lightly silicified diatom that does not preserve well in sediments, has been linked to increased eutrophication combined with silica limitation (Parsons et al., 2002). Although diatom preservation may be enhanced in anoxic sediment with reduced densities of bioturbating animals (McMinn, 1995), this factor does not seem to be responsible for patterns in the diatom record for the northern Gulf of Mexico (Parsons et al., 2002). In four cores from a part of Chesapeake Bay where anoxic periods are most prevalent and severe, Cooper and Brush (1993) and Cooper (1995) detected a decrease in diatom diversity that began around 1760 and became particularly marked in recent sediments. ...
Under certain conditions, sediment cores from coastal settings subject to hypoxia can yield records of environmental changes over time scales ranging from decades to millennia, sometimes with a resolution of as little as a few years. A variety of biological and geochemical proxies derived from such cores have been used to reconstruct the development of eutrophication and hypoxic conditions over time. Proxies based on 1) the preserved remains of benthic organisms (mainly foraminiferans and ostracods), 2) sedimentary features (e.g. laminations) and 3) sediment chemistry and mineralogy (e.g. presence of sulphides and redox-sensitive trace elements) reflect conditions at or close to the seafloor. Those based on 4) the preserved remains of planktonic organisms (mainly diatoms and dinoflagellates), 5) pigments and lipid biomarkers derived from prokaryotes and eukaryotes and 6) organic C, N and their isotope values reflect conditions in the water column. However, the interpretation of these proxies is not straightforward. A central difficulty concerns the fact that hypoxia is strongly correlated with, and often induced by, organic enrichment (eutrophication), making it difficult to separate the effects of these phenomena in sediment records. The problem is compounded by the enhanced preservation in anoxic and hypoxic sediments of organic microfossils and biomarkers indicating eutrophication. The use of hypoxia-specific indicators, such as the trace metals molybdenum and rhenium and the bacterial biomarker isorenieratene, which have not been used often in historical studies, may provide a way forward. All proxies of bottom-water hypoxia are basically qualitative; their quantification presents a major challenge to which there is currently no satisfactory solution. Finally, it is important to separate the effects of natural ecosystem variability from anthropogenic effects. Despite these problems, in the absence of historical data for dissolved oxygen concentrations, the analysis of sediment cores can provide plausible reconstructions of the temporal development of human-induced hypoxia, and associated eutrophication, in vulnerable coastal environments.
... , 20-40 µm,5-6 µm, 10 µm 11 : : (Hasle, 1965(Hasle, , 1968Round et al., 1992;Hasle & Syvertsen, 1997) (Mcminn, 1995), (Abbott, 1974 Arch. Hydrobiol. ...
A nanodiatom genus, Fragilariopsis Hustedt, is newly recorded in China. This genus is characterized by, (1) cells in ribbons united by the entire or the greater part of the valve surface, (2) raphe strongly eccentric, (3) approximately equal numbers of interstriae and fibule, (4) apical axis often heteropolar, and (5) striae with two rows of poroids, seldom one or more than two. A detailed description of the taxonomic characteristics of the genus is given. The two species distributed in East China Sea and Huanghai Sea of China, F. kerguelensis (O'Meara) Hustedt and F. rhombica (O'Meara) Hustedt, were observed under TEM and photographed.
The study presents the first lacustrine diatom record spanning a sequence down to the latest Weichselian (ca. 11.000 y BP) from Taymyr Peninsula, NW-Siberia. The aim of this contribution is to assess the development of Lama Lake (NE Norilsk) from the changes in diatom assemblage composition within the context of local pollen assemblages (Hahne and Melles, this volume) and sedimentological/ geochemical data.
Several features of the diatom assemblages of Lama Lake sequence are related to the establishment of microhabitats in marginal areas: stable background‘ percentages of alphameso to eutrophic taxa throughout the sequence, distinctive fluctuations in diversity indices and the record of acidophilus taxa, all of which rely on occurrence patterns of periphytic taxa. The large water body is considered to act as a buffer against environmental changes which are thus less strongly reflected by the diatom assemblages.
From a general agreement between main features of diatom (ratio of euplanktonic/nonplanktonic taxa) and pollen (ratio of arboreal/non arboreal pollen) data trends, changes in lake water surface temperature are inferred.
The distinctive maxima of certain diatom taxa and their specific ecological preferences for thermal and trophic conditions, as well as the pronounced succession of planktonic species maxima, enable us to assess trends in these lake parameters. However, a much higher temporal resolution is needed to resolve timing effects in the responses of terrestrial and aquatic ecosystems.
In January-February 1988, >40 diatom species were found in Prydz Bay. Small pennate diatom species (<20 μm), Nitzschia cylindrus, Nitzschia closterium and Nitzschia curta, dominated at all drill sites and were distributed ubiquitously along the transect of sampling sites, while larger-celled (>20 μm) diatom species, Chaetoceros dichaeta, Chaetoceros neglectus, and Corethron criophilum, were concentrated in the inner part of Prydz Bay. The smaller-celled diatom species influenced the total diatom cell density and showed similar patterns of distribution to the totals, whereas profiles of the larger-celled diatom species showed similar patterns to the chlorophyll a concentration. -from Authors
Spring phytoplankton communities in the water column of Ellis Fjord are characterized by diatoms originating from the bottom
sea-ice strand community. Upon ice breakout in early summer, these are replaced by blooms of the phytoflagellates, Phaeocystis pouchetii, Cryptomonas cryophila, Pyramimonas gelidicola, silicoflagellatcs and dinoflagellates. The narrow entrance of the fjord and the development of summer stratification is
probably limiting the availability of nutrients and containing the magnitude of the small bloom (maximum 2.8 × 106 cells l−1).
Cleaned Pliocene diatoms from Pacific deep-sea sediments were exposed to natural sea water in a laboratory experiment to study diagenetic alterations of diatom assemblages. After 200 hours of exposure to sea water most diatom valves showed noticeable dissolution effects. A smaller group of diatoms showed silica overgrowth, which apparently was initiated around the areolae of the valve surfaces. There is thus experimental evidence for the simultaneous occurrence of silica dissolution and overgrowth in diatom diagenesis.
Two diatom frustule dissolution experiments (DE1 and DE2) were performed on material from Lakes Geneva and Nantua, SE France. In DEl, the dissolution of diatom silica from sediments was measured over a 92-d period at room temperature in six 3 M salt solutions (NaCl, Na,CO,, KN09, CaCl,, LiN03, MgCl,), in 0.6 M NaCl, and in distilled water. As expected, dissolution was greatest in Na,CO, where high pH leads to ionic dissociation. A similar process was also apparent in solutions of KNO, and LiNO, which were only slightly alkaline. In contrast, weakly acid solutions of MgCl, and CaCl, produced less dissolution than distilled water. Between 0.6 and 3 M NaCI, silica solubility appeared to reach an undetermined optimum which could correspond to minimum values of ion activity coefficients. In a second experiment (DE2), the dissolution of living diatoms from Lake Geneva was monitored over 46 d in 3 M solutions of Na,CO, and NaCl and in distilled water. The results were not in accordance with the expected theoretical levels predicted by Pitzer's equations when applied to silica solubility in con- ccntrated solutions. Clear interspecific differences in diatom dissolution rates occurred in both experi- ments. The gross valve surface area : volume ratio was found to bc a useful first-order approximation of a particular diatom species' propensity to dissolve. Only minor differences in diatom assemblage com- position were observed in NaCl solutions over the experimental period whereas major changes were caused by Na,CO, solutions.
A transfer function has been established to quantify the dissolution of diatom silica in Southern Ocean sediments. The relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box-core tops, each representative of a modern diatom species sediment assemblage. The amount of dissolved silica was measured for each experiment. The resulting data set of species abundances (42 samples containing 32 diatom species and 2 silicoflagellate genera) was added to the modern data base of diatom species distributed over the Southern Ocean (124 core tops). Q-mode factor analysis individualizes four factors explaining 83% of the variance. The first three factors are controlled by surface water properties (mostly temperature). The fourth factor is the only one correlated with loss of silica in the reference samples (R = 0.900). We quantified the dissolution factor using this correlation: superficial sediments of the Southeast Indian Ocean are characterized, from low to high latitudes, by a decrease in silica loss by dissolution (from >50 to 10%) from the Subantarctic Zone (40°S) to around 55°S, followed by an increase of silica loss to values larger than 60% between 63° and 68°S. Application of the dissolution factor in two cores from the Southern Ocean (≈44° and 55°S) shows enhanced opal dissolution during the last glaciation, particularly during Emiliani's stage 3 (from 40,000 to 30,000 yr B.P.).
Diatom assemblage and preservational data are used to reconstruct paleoceanographic conditions at the last glacial maximum (18,000 yrs BP) in the Southern Ocean. From these data, the following points can be made about the last glacial maximum in this region. (1) Contraction and slight northern shift of the belt of well preserved diatoms appears to be related to the northward shift of late spring/early summer sea ice cover. (2) Presence of open-ocean, though poorly preserved, diatom assemblages to the south of this belt strongly suggest that, during many summers, large areas of the Southern Ocean were ice-free. (3) The distribution of theNitzschia kerguelensis factor, both in surface sediments and at the last glacial maximum, indicates that the gyre systems, particularly the Weddell Gyre, were intensified during glacial times. (4) Although data are sparse in the higher-latitude South Atlantic, there is an indication that the Weddell Polynya also existed during glacial times, although it was shifted a few degrees northward.
Three assemblages of Quaternary siliceous microfossils were dissolved for varying lengths of time in natural seawater. Changes in the relative abundances of certain radiolarians, diatoms, and sponge spicules were measured, and a dissolution index scheme was developed. This scheme allows an objective assessment of the preservation of tropical siliceous microfossil assemblages of Quaternary age. Its application to a study of near-surface sediments in the eastern tropical Pacific shows that the siliceous microfossil preservation pattern roughly reflects surface water productivity. Two second-order features are superimposed upon this pattern. First, preservation is usually better at deeper depositional sites at most latitudes, and this is attributed primarily to sediment redistribution processes. Second, the best preservation is found not in equatorial sediments, but in those obtained from an area near 10°N, 117°W. This is attributed to the unusually high abundance of fragments of the diatom genus Ethmodiscus found in those sediments.
Physico-chemical data and isotopic studies (utilising H14CO3, H2
18O, 3H2O) suggest that hypersaline meromixis in Ellis Fjord (Vestfold Hills, Antarctica) was initiated during the middle Holocene period, when hypersaline brine, excluded during the annual formation of sea-ice, gravitated in a density current to the bottom. The application of this contemporary information to the genesis of the meromictic lakes found today in the Vestfold Hills, suggest that their meromixis may have developed prior to isolation from the sea. Comparison of physico-chemical data from the meromictic basins of Ellis Fjord with that of the Vestfold Hills saline lake allows some determination of their evolutionary pathways initiated before, during and after isolation from the sea. Further evolution of each lake can be explained through the individual interaction between climate, the catchment size and basin morphology.