Article

Corrigendum to “Marine organic geochemistry of the Eastern Mediterranean: 2. Polar biomarkers in Cretan Sea surficial sediments” [Marine Chemistry 85 (2004) 1–25]

March 2004
Marine Chemistry

March 2004

DOI:10.1016/j.marchem.2003.08.005

Authors:

Alexandra Gogou

Hellenic Centre for Marine Research

Euripides G Stephanou

University of Crete

Lipid biomarkers and the organic carbon content have been determined in sediments collected from two transects across the continental shelf and slope (100 to 1500 m) in the oligotrophic Cretan Sea (Eastern Mediterranean). In general, concentrations (absolute and with respect to total organic carbon) of most biomarkers of both marine and terrestrial origin are attenuated with depth and with increasing distance from land. The low abundance of compounds that can be ascribed to primary producers (PP) (247–3589 ng/g of sediment and 5.2 to 23.6% of total lipids), namely diatoms, coccolithophorids, dinoflagellates, and nanoplankton species, reflects the low productivity in surface waters, along with the significant re-working of planktonic organic material prior and/or after burial. This re-working has been attributed to microorganisms, zooplankton and benthic invertebrates, with their specific biomarkers concentrations ranging from 111 to 755 ng/g (microorganisms) and from 157 to 2963 ng/g (zooplankton and invertebrates). Finally, the results on the abundance of terrestrial n-alkanals, n-alkanols and n-alkanoic acids, conjointly with those on terrestrial n-alkanes, presented in a previous paper (Mar. Chem. 68 (2000) 265) show that the terrestrial signal is an important fraction of total lipids in Cretan Sea sediments (13.0% to 51.7%). Its relative abundance shows an increase from the shallow station of the continental shelf (23.2%) to the deep basin station (51.7%), indicating a more persistent character of the terrestrially derived compared to the marine-derived component.

Evidence of spatial and temporal changes in sources of organic matter in estuarine sediments: Stable isotope and fatty acid analyses

Article

Full-text available

May 2014

We investigated spatial and temporal changes in sources of organic matter in sediments within an estuarine environment in South Africa using fatty acids (FA) and stable isotopes (SI). Samples of sediments and sources of organic matter [i.e., particulate organic matter, microphytobenthos (MPB), macrophytes, salt marsh plants, and terrestrial leaves] were collected during spring and summer 2012, and autumn and winter 2013 from the upper, middle, and lower reaches. A Stable Isotope Analysis in R (SIAR) mixing model was used to identify the organic matter sources contributing to sediments in each estuarine reach and season. We found that diatom-associated fatty acids (20:5ω3; 16:1ω7) increased toward the upper reaches, while long-chained terrigenous fatty acids (24:0) tended to be more prevalent in lower reach sediments. In support of the FA results, the SI mixing model showed a substantial contribution from the marsh grass Spartina maritima in sediments of the lower estuary during periods of low-freshwater discharge (autumn and winter), while MPB was the main component in sediments from the upper and middle reaches during all seasons. Our results have implications for evaluating estuarine food webs since the spatial and seasonal variability in the organic matter deposited can influence estuarine community structure.

Molecular biomarker evidence of origins and transport of organic matter in sediments of the Pearl River estuary and adjacent South China Sea

Article

Full-text available

Sep 2009
APPL GEOCHEM

Surface sediments from the subtropical Pearl River estuary and adjacent South China Sea were investigated by molecular organic geochemical methods to determine the composition, distribution and origin of extractable lipids (n-alkanes, n-alkanols and sterols). The absolute and organic C normalized concentrations of total alkane, n-alkanol, and sterol ranged from 0.16 to 2.67 μg g−1 and 0.9 to 12.3 μg g−1 OC, 24.4 to 427.3 ng g−1 and 63.2 to 1966.7 ng g−1 OC, and 9.0 to 493.5 ng g−1 and 58.4 to 1042.4 ng g−1 OC, respectively. The spatial distributions of these biomarkers indicated that terrestrial-derived molecular biomarkers such as long-chain n-alkanes, n-alkanols and plant-derived sterols were higher at the river mouth and along the coastline, suggesting that a higher proportion of terrestrial particulate organic matter was deposited there. Relatively lower amounts of marine-derived biomarkers such as short-chain n-alkanes, algal sterols at the river mouth reflected the lower primary productivity due to high turbidity. The spatial patterns of these biomarkers were partially related to the estuarine processes and conditions, evidencing an increased terrestrial signal from the Pearl River mouth to the inner estuary, and enhanced marine conditions further offshore.

Biomarcadores ácidos grasos y relaciones tróficas en macroinvertebrados bentónicos marinos

Research

Full-text available

Sep 2009

Julio César Marín Leal

The lipids, and particularly the fatty acids, have been widely used to study trophic interactions between marine macroinvertebrates in trophic networks of coastal environments. This approach is allows to know the contribution of different particulate organic matter sources (POMS) to the nutritional regime of the benthic macrofauna, thanks to the identification of specific fatty acid biomarkers, such as of diatoms, flagellated, terrestrial plants, bacteria, etc. In the present work the seasonal dynamics of the fatty acid profiles of different FMOP was studied, as well as of several species of benthic suspensivores in two ecosystems of the region of Normandy (France), destined to culture of the oyster Crassostrea gigas: the Bay of Veys (BDV) and the zone of Lingreville (LIN). In the BDV, samples of C. gigas, Mytilus edulis, Cerastoderma edule, Crepidula fornicata and Lanice conchilega were collected, whereas in LIN C. gigas, M. edulis, C. fornicata and Sabellaria alveolata were captured. The monitored POMS in both sites were: marine organic matter (mainly phytoplankton; MOM), terrestrial organic matter (TOM), sedimented organic matter (SOM), microphytobenthos (MPB), as well as the macroalgae Ulva lactuca and Fucus serratus. The analyses of fatty acid methylic esters by gas chromatography, connected to a mass detector, showed the presence of ubiquitous fatty acids, as the 16:0 and 18:0, as well as of more specific biomarkers, as 18:1(n-7) (bacterial), 20:5(n-3) (diatoms) and 18:1(n-9) (brown macroalgae). The multivariate analyses discriminating between the benthic macroinvertebrates based on their fatty acid profiles. These profiles exhibited fort temporary variations, indicating that the diatoms act as the main food source for the studied suspensivores (> 25% in M. edulis of the BDV), particularly during spring and summer. The bacteria contributed during autumn and winter, whereas the signature of terrestrial plants was insignificant. The presence of non-methylene interrupted dienoic acids (NMID) in the macroinvertebrates was detected, such as 20:2Δ5,11; 20:2Δ5,13; 22:2Δ7,13 and 22:2Δ7,15. The trophic and hydrologic characteristics of both ecosystems determined the contribution differential of POMS, showing a greater diversity of sources ingested under the estuarine influence of the BDV (intersite differences).

Interactions trophiques entre l’huître creuse Crassostrea gigas et les suspensivores benthiques dans deux écosystèmes intertidaux en Basse-Normandie : utilisation des isotopes stables naturels (δ13C, δ15N) et des profils acides gras

Thesis

Full-text available

Oct 2007

Julio César Marín Leal

Shellfish culture zones are singular ecosystems where particulate organic matter sources (POMS) are diverse and where interspecific trophic relations between benthic suspensivores are particularly complex. In this study, the compositions of both natural stable isotopes (δ13C and δ15N) and fatty acid biomarkers were used to evaluate the temporal dynamic of POMS contributions (marine organic matter (PhyOM), microphytobenthos (MPB), terrestrial organic matter (TOM), sedimented organic matter (SOM) and the macroalgae Ulva sp. and Fucus serratus) to the diet of the oyster Crassostrea gigas and of its potential competitors i.e.Mytilus edulis, Cerastoderma edule, Crepidula fornicata, Lanice conchilega and Sabellaria alveolata, this in two contrasted ecosystems of Normandy (France) : the Bay of Veys (BDV) and Lingreville (LIN). The isotopic approach has shown that PhyOM was the main food source for bivalves, particularly in LIN due to the strong marine influence. However, the MPB and the TOM detritus as well as the macroalgae contributed to the diet of suspensivores during the summer and the autumn in BDV. This discovery was confirmed by the seasonal monitoring of fatty acid biomarkers, which has shown a high contribution of the diatoms and also a significant contribution of bacteria. The dynamic of the trophic relations of macroinvertebrates was time-dependent, according to the seasonal character of food available. The interspecific competition is not very likely because the species have shown the capacity to use the various sources available along the year and especially for C. fornicata, L. conchilega and S. alveolata.

Atmospheric and Oceanographic Forcing Impact Particle Flux Composition and Carbon Sequestration in the Eastern Mediterranean Sea: A Three-Year Time-Series Study in the Deep Ierapetra Basin

Article

Full-text available

Feb 2021

Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the biotic composition and seasonal variability of sinking particles reaching abyssal depths. Herein, sinking particle flux data, collected in the deep Ierapetra Basin for a three-year period (June 2010 to June 2013), have been examined at the light of atmospheric and oceanographic parameters and main mass components (lithogenic, opal, carbonates, nitrogen, and organic carbon), stable isotopes of particulate organic carbon (POC) and source-specific lipid biomarkers. Our aim is to improve the current understanding of the dynamics of particle fluxes and the linkages between atmospheric dynamics and ocean biogeochemistry shaping the export of organic matter in the deep Eastern Mediterranean Sea. Overall, particle fluxes showed seasonality and interannual variability over the studied period. POC fluxes peaked in spring April–May 2012 (12.2 mg m⁻² d⁻¹) related with extreme atmospheric forcing. Summer export was approximately fourfold higher than mean wintertime, fall and springtime (except for the episodic event of spring 2012), fueling efficient organic carbon sequestration. Lipid biomarkers indicate a high relative contribution of natural and anthropogenic, marine- and land-derived POC during both spring (April–May) and summer (June–July) reaching the deep-sea floor. Moreover, our results highlight that both seasonal and episodic pulses are crucial for POC export, while the coupling of extreme weather events and atmospheric deposition can trigger the influx of both marine labile carbon and anthropogenic compounds to the deep Levantine Sea. Finally, the comparison of time series data of sinking particulate flux with the corresponding biogeochemical parameters data previously reported for surface sediment samples from the deep-sea shed light on the benthic–pelagic coupling in the study area. Thus, this study underscores that accounting the seasonal and episodic pulses of organic carbon into the deep sea is critical in modeling the depth and intensity of natural and anthropogenic POC sequestration, and for a better understanding of the global carbon cycle.

Determination and geochemical implication of multiple series of long-chain oxygen-bearing compounds trapped in kerogen in the Lucaogou Formation, Santanghu Basin, NW China

Article

Apr 2018
ORG GEOCHEM

Studies of occluded oxygen-bearing compounds inside kerogen are scarce, although such studies are important in understanding early-stage transformation of organic matter. A relatively low-maturity kerogen from the late Permian mudstone of the Lucaogou Formation of the Santanghu Basin, northwestern China, was successively extracted with n-hexane, acetone and dichloromethane to release the adsorbed components, and the extracted kerogen was treated with a mild oxidation reagent H2O2 to release the occluded components. Gas chromatography–mass spectrometry analysis of the adsorbed and occluded components revealed a suite of oxygen-bearing compounds, including n-alkan-2-ones, n-aldehydes and fatty acid methyl esters. The n-alkan-2-ones were mainly detected in the adsorbed fraction and n-aldehydes in the occluded component. Comparison of the long-chain oxygen-bearing compound distributions and their individual stable carbon isotope characteristics both suggest that the oxygen-bearing compounds released by H2O2 treatment were occluded in the kerogen. The shorter-chain (C15 to C19) occluded n-aldehydes reflected similar isotopic distribution trends to the adsorbed n-alkan-2-ones, and the δ¹³C values of the mid-length (C21 to C25) occluded n-aldehydes were much closer to the adsorbed n-alkanes. Bacterially mediated methylation and decarbonylation of the n-aldehydes during kerogen formation may be important source(s) of n-alkan-2-ones and n-alkanes, respectively. The mid-chain ketones mainly originated from hydrothermal alteration of n-alkanes after kerogen formation. Uplift of the Lucaogou Formation in the Yuejingou section allowed surface-enhanced aerobic reactions.

Late postglacial paleoenvironmental change in the northeastern Mediterranean region: Combined palynological and molecular biomarker evidence

Article

May 2012
QUATERN INT

Three gravity cores collected from the NE Mediterranean (NEMR) across a transect from the northern Aegean Sea (North Skyros basin) to the south Cretan margin (SCM), were investigated for pollen and terrestrial biomarkers derived from epicuticular waxes of vascular plants during the last w20 ky. Pollen data show diversified mixed temperate forest in the northern borderlands and enhanced Mediterranean vegetation in the southern areas, documenting an NeS climatic trend. Terrestrial plant biomarkers and their diagnostic geochemical indices exhibit latitudinal patterns which are interpreted in terms of the different delivery pathways (fluvial/runoff vs. atmospheric transport), resulting from the climate conditions during different periods. During the Late Glacial and early deglaciation periods (20e14 ka BP) relatively increased humidity (H-index) is recorded in the north Aegean Sea, while in the South drier climate was the limiting factor for vegetation development. During this interval, terrestrial n-alkanes showed increased accumulation rates, suggesting massive transport of terrestrial organic matter through runoffs and rivers, followed by weaker input after 14 ka BP. After w11 ka BP a major expansion of forest cover is evidenced in the NEMR, accompanied by a higher H-index because of the climatic amelioration. The forest vegetation exhibited regionally different characteristics, with cool temperate taxa being more abundant in the Aegean cores, while the SCM record is being featured by Mediterranean elements. At the onset of the Holocene and throughout the Holocene Climatic Optimum the delivery of terrestrial biomarkers increased and became more significant in the Aegean sites compared to the SCM site. Within the Holocene, the average chain length (ACL) of long chain n-alkanes exhibits lower values in the northern Aegean than in the southeastern Aegean and SCM, indicating the predominance of warmer species southwards. Finally, the H-index records a conspicuous humidity increase between 5.4 and 4.3 ka BP in the south Aegean that coincides with an increase in the terrestrial biomarker supply and the deposition of a distinct sapropel-like layer, SMH (Sapropel Mid Holocene). Similar trends in T (temperature) and H indices are slightly delayed and attenuated in the northern Aegean and are accompanied by an increase in the ACL index. A noticeable increase in the accumulation rates (ARs) of terrestrial biomarkers and the HPA index values during this period are clearly recorded in all three cores, indicative of enhanced terrigenous inputs of organic matter along with higher in-situ preservation.

Detection of Water and Sediments Pollution of An Arid Saltern (Sfax, Tunisia) by Coupling the Distribution of Microorganisms With Hydrocarbons

Article

Full-text available

Nov 2007

We investigated the coupling of abundance of bacteria, phytoplankton and ciliates with hydrocarbons in the surface water and sediments of five interconnected ponds in the arid Sfax solar salterns. This study aimed at determining the potential sources of hydrocarbons and the effects of salinity gradients on microorganism metabolism. Hydrocarbon analysis was performed by gas chromatography (GC-FID) and gas chromatography coupled with mass spectrometry (GC-MS). The GC-FID allowed the detection of aliphatic hydrocarbons and n-alkanes ranging from n-C13 to n-C30. Total aliphatic hydrocarbon concentrations varied from 92.5mg. l−1 in the first pond (having marine characteristics) to 661.1mg. l−1 in the last pond (crystallizer) (316.8 ± 120.1mg. l−1) for water samples and from 26.7 to 127.8μg. g−1 dry weight for sediment samples. The GC-MS enabled us to detect halogenated hydrocarbons (bromoalkanes and chloroalkanes) and n-alkenes. The distribution of n-alkanes indices coupled to several environmental factors suggests that a major fraction of hydrocarbons resulted from both prokaryotic (bacteria) and eukaryotic (protists) developments. A low hydrocarbon fraction might be petrogenic.

Organic geochemical evidence of Late Glacial–Holocene climate instability in the North Aegean Sea

Article

Nov 2007
PALAEOGEOGR PALAEOCL

Sedimentary molecular biomarker compositions, organic carbon and CaCO3 concentrations, and bulk organic δ13C and total δ15N values document a series of paleoclimatic changes that have affected organic matter production and sedimentation in the North Aegean Sea from the termination of the latest glacial maximum through the middle Holocene. Continental environmental conditions have been inferred from land–plant biomarkers. Paleoproductivity patterns of diatoms, prymnesiophytes, dinoflagellates, and nannoplankton were discerned from marine-derived biomarkers. Although organic matter is predominantly marine, variations in the proportion of marine and land contributions and in its general preservation are evident. Rapid changes in the Eastern Mediterranean thermohaline circulation evidently occurred in parallel to sea surface temperature oscillations. Enhanced deep-water ventilation accompanied cold intervals in the late Last Glacial, the Younger Dryas, and during an interruption of deposition of the S1 sapropel, probably in response to strengthening of north winds over the region. In contrast, decreased thermohaline circulation occurred during the warm interval associated with the S1 sapropel. During this period, increased freshwater inputs diminished ventilation of deep-water masses and enhanced organic matter production and preservation. Intriguing fluctuations in sea-surface temperatures and the concentrations of marine and terrestrial biomarkers within the sapropelic layer, most prominently in the interruption from 8.2 to 7.8 calibrated radiocarbon conventional kyr BP, support the hypothesis that several distinct events of deep water reoxygenation occurred in the North Aegean Sea during deposition of the S1 sapropel. These events reflect centennial excursions to the more common low-productivity and well ventilated conditions of the Mediterranean that may possibly be related to North Atlantic Oscillation cycles.

Lipid biomarker record in surface sediments at three sites of contrasting productivity in the tropical North Eastern Atlantic

Article

Jan 2008
MAR CHEM

Selected lipid biomarkers were analyzed in modern aerobic surface sediments from the tropical NE Atlantic off the Mauritanian coast, in the frame of the JGOFS EUMELI program. This paper explores how sedimentary molecular proxies record productivity and vascular plant inputs. Dry weight-normalized concentrations and TOC-normalized concentrations of biomarkers poorly matched the gradient of higher-plant inputs and of primary productivity. In contrast, mass accumulation rates of long-chain n-alkanols and n-fatty acids (80–710 and 210–1750 μg m− 2 yr− 1, respectively) showed good agreement with dust inputs transported between 15 and 24°N by NE trade winds, whereas long-chain n-alkanes showed a distinct pattern. At the coastal site, n-alkanols and n-fatty acids predominated over long-chain n-alkanes. Cross-shelf changes in proportions of n-fatty acids and n-alkanols relative to n-alkanes point to an increased degradation of terrigeneous waxes when going offshore. The cross-shelf C/N ratio poorly registered vascular plant inputs, most probably because denitrification influenced C/N values at the eutrophic site.Mass accumulation rates of phytoplanktonic biomarkers declined from the eutrophic to the oligotrophic site, reflecting the primary productivity variation. Mass accumulation rates of highly branched isoprenoid hydrocarbons, C37 n-alkenones, n-alkyl diols and dinosterol varied from 3 to 410, 9 to 1600, 12 to 360 and 7 to 320 μg m− 2 yr− 1, respectively. They target the productivity of Haslea-type diatoms, coccolithophorids, eustigmatophytes and dinoflagellates. While the results encourage the development of molecular proxies of palaeoproductivity and of palaeophytocommunities, progress is still needed to deconvolute the impact of degradation on mass accumulation rates and to move towards quantitative calibrations.

Spatial distribution of hydrocarbons in the Shatt Al-Arab River and the Northern Coast of the Arabian/Persian Gulf Characteristics, sources and environmental impacts

Article

Full-text available

Jun 2024

Spatial distribution of hydrocarbons in the Shatt Al-Arab River and the Northern Coast of the Arabian/Persian Gulf

Chapter

May 2024

Grain size controls on long-chain diol distributions and proxy signals in marine sediments

Article

Full-text available

Oct 2022

Long chain alkyl diols (LCDs) are lipid biomarkers that occur ubiquitously in sediments. Their abundance and distributions are increasingly used as the basis of molecular proxies for environmental parameters such as sea surface temperature (SST) via the Long chain Diol Index (LDI), and upwelling intensity and nutrient conditions (parametrized as diol indices, DI-2, and Nutrient Diol Index, NDI, respectively). Their marine producers remain the subject of debate, but in cultures, they can be found within the outer wall (algaenan) of eustigmatophytes or in Proboscia diatoms. LCDs appear to be well preserved in sediments, potentially as a result of their association with algaenan and/or minerals, but little is known of their pre-depositional histories, in particular transport dynamics. Here, 15 surface continental margin sediments as well as one high-deposition-rate sediment core (50 cm, spanning the last ~30 years) were analyzed in order to evaluate the impact of organo-mineral associations, lateral transport, and hydrodynamic sorting on sedimentary LCD signals. The abundance and distribution of LCDs in bulk sediments and corresponding grain-size fractions was determined. The highest proportion of all LCD isomers is found in the fine fraction (2 – 10 µm), which also holds the highest proportion of organic matter in relation to the other grain-size fractions. However, LCDs are also found in the other fractions (sand, coarse silt, and clay), and their concentrations are not correlated with bulk organic carbon content, indicating different preservation or transport mechanisms. LDI-SST in the bulk sediment is comparable to the mean annual SST at all sites except those influenced by upwelling and characterized by strong seasonal SST gradients. To the contrary of other biomarker-related proxies (e.g., alkenones), lateral transport does not appear to strongly affect LDI-SST in size fractions, suggesting that the intimate relationship of LCD with the algaenan may counteract the influence of hydrodynamic mineral sorting processes on related proxy signals. The difference between the fraction-weighted LCD concentration and bulk sedimentary LCD concentration indicates potential release of LCD during laboratory fractionation, suggesting degradation of algaenan or dissolution of opal frustules.

Organic matter diagenesis and precipitation of Mg-rich carbonate and dolomite in modern hypersaline lagoons linked to climate changes

Article

Full-text available

Sep 2022
GEOCHIM COSMOCHIM AC

Lipid-biomarkers have been used to reconstruct environmental changes in lacustrine systems on a range of time scales. Lake sediments are excellent archives to apply these tools due to their rapid and amplified response to environmental pressures. For the past thirty years, the hypersaline lagoons of the Rio de Janeiro coastal plain have been studied as natural laboratories for the observation of the biogeochemical processes involved in modern dolomite precipitation. Here, we apply a multiproxy approach to characterize two depositional stages during the Holocene that may have triggered primary dolomite formation in these lagoonal environments. A first stage, with two sub-stages (1A - 6.1 to 4.2 kyr. BP; 1B - 4.2 to ∼3.6 kyr. BP) was deposited during the sea-level rise, with sediments containing an abundance of long-chain n-alkanes with ²H-depleted (δ²Hn-alk) signatures indicating riverine inputs of terrestrial organic carbon during prevailing wet conditions. A second stage (< ∼3.6 kyr. BP), comprising lacustrine facies, was characterized by high amounts of authigenic carbonate precipitates (calcite, Mg-calcite, Ca-dolomite, and dolomite). The carbonates are the result of physico-chemical changes in the water after the isolation of the lagoons from both the Atlantic Ocean and the neighboring Lagoa de Araruama due to a fall in sea level and aridification associated with intensification of the coastal upwelling after 2.2 kyr. BP. The n-alkanes deposited during this phase contain variable proportions of long and short-chain homologues indicating a mixed source of organic matter (terrestrial higher plants and microorganisms), as well as changes in vegetation associated with the driest conditions, inferred from the ²H-enriched n-alkane homologous. These results clearly demonstrate a climatic influence on dolomite formation in coastal hypersaline environments linked to sea-level change and coastal upwelling phenomena. With these observations, we hypothesize that the existence of similar palaeoceanographic and environmental conditions in the geologic past may have triggered the formation of extensive microbial dolomite deposits. This study provides new elements to interpret the formation of massive dolomite deposits in the geological record, for example, along the Late Triassic Tethys margin.

Natural and anthropogenic sources of extractable organic matter in sediments from the coastal zone of the Arabian Gulf in Saudi Arabia

Article

Aug 2022

Surface sediment samples from the Arabian Gulf coast of Saudi Arabia were collected by Van Veen grab sampler to identify the characteristics, distribution, and levels and to discriminate between natural and anthropogenic sources of the total extractable organic matter (TEOM). The dried and sieved sediments were extracted with a dichloromethane/methanol mixture for analysis by gas chromatography-mass spectrometry. The TEOM included n-alkanes (353.9±283.8 ng.g−1), n-alkanols (283.2±296.1 ng.g−1), fatty acid methyl esters (245.2±353.7 ng.g−1), hopanes (100.7±158.2 ng.g−1), steranes (58.5±96.3 ng.g−1), triterpenoids (18.9±21.1 ng. g−1), steroids (15.3±17.0 ng.g−1), polycyclic aromatic hydrocarbons (PAHs) (0.48±1.19 ng.g−1), as well as an unresolved complex mixture (UCM=1633±3151 ng.g−1) and petrochemicals (343.1±424.2 ng.g−1). The major sources of these TEOM compound groups were anthropogenic (petroleum and petrochemical) and natural (lipids from higher plants, marine material, and microbiota) inputs. Anthropogenic contaminants from petroleum products ranged from 46.6 to 85.6% of the TEOM, whereas petrochemicals varied from 10.7 to 40.6%. The biogenic influx from terrestrial vegetation ranged from 5.7 to 19.3%, and marine biotic sources varied from 11.1 to 37.5%. The continuous accumulation of anthropogenic contaminants will ultimately affect the critical habitats of this marine coastal region. This provides a basis for further studies to understand human and developmental activities on input delivery, deposition processes, distribution, and biogeochemical alteration of organic matter in the coastal zones of the Arabian Gulf. Such studies are important for the sustainable development and protection of these key regional habitats.

Characteristics and Kinetics of Hydrous Pyrolysis of Scrap Tire Rubber at Temperatures from 150 oC to 400 oC

Article

Jan 2021

Pyrolysis experiments in presence of water, with and without oxalic acid, were performed on passenger tire waste to determine the conversion rate constants, order of the reactions, activation energy, and frequency factor for the oil-like product yields. The pyrolysis experiments were performed at temperatures of 150oC-400oC and different heating times. The oxalic acid was added to enhance the reaction by providing excess hydrogen. The major reaction products were n-alkanes, fatty acids, hopanes, phenols, quinolines, and UCM at T < 350oC, and mainly PAHs at T > 350oC. The yields (g/g) increased with the increase of temperature, heating time, and the presence of oxalic acid in the reaction mixtures. The yields of oil-like hydrocarbon products were maxima at 350oC and decreased above 400oC for both sets of experiments. The reaction rate constants were 4.164x10-7 - 3.299x10-6 (Y0.5 s-1) in the absence of oxalic acid and 4.266x10-7 - 3.677x10-6 (Y0.5 s-1) in the presence of oxalic acid. The total orders of the reactions are 0.47±0.03 without and 0.49±0.07 with oxalic acid, respectively. The measured activation energies were 2.0878x104 and 2.0212x104 (kJ mol-1) and the frequency factors were 1.563x10-4 and 1.502x 10-4 (Y0.5 s-1) in the absence and with oxalic acid, respectively.

Early Diagenesis of Organic Matter in two Lacustrine Evaporitic Environments in Brazil

Conference Paper

Jan 2021

Lipid Tracers in Coastal Sediments of the Northwestern Arabian/Persian Gulf: Characteristics, Sources, Distribution, and Possible Ecological Impacts

Chapter

Nov 2020

Ahmed I. Rushdi

This chapter discusses the levels, distribution, and sources of oil pollutants relative to other organic matter in surface sediments of the northwestern of the Arabian/Persian Gulf. The sediment samples were collected from the coasts of Iraq and Saudi Arabia by grab samplers. They were extracted with a dichloromethane/methanol mixture after drying and analyzed by gas chromatography-mass spectrometry (GC-MS). The lipid compounds in the sediments include n-alkanes (4.5-5.8% for Iraq and 0.0-22.2% for Saudi Arabia), methyl n-alkanoates (1.5-4.1% for Iraq and 16.1-41.8% for Saudi Arabia), n-alkanols (6.8-7.8% for Iraq and 13.6-45.9% for Saudi Arabia), hopanes (2.5-5.1% for Iraq and 0.1-5.0% for Saudi Arabia), steranes (2.1-3.1 for Iraq and 0.0% for Saudi Arabia), plasticizers (29.1-39.9% for Iraq and 3.0-29.4% for Saudi Arabia), and UCM (unresolved complex mixture) (36–52% for Iraq and 6–47% for Saudi Arabia). The major sources of these lipid compounds are from anthropogenic petroleum inputs (41.1-61.2%) and plasticizers (29.1-39.9%) in the coast of Iraq, with lesser amounts in the coastal zone of Saudi Arabia (9.4-39.5% for petroleum and 2.9-24.2% for plasticizers). The inputs from natural sources in the coast of Iraq range from 9.7% to 13.1% and from 31.1% to 55.1% in the coast of Saudi Arabia. Petroleum product deposits and plastic additives to the coastal sediments of the Gulf likely have effects on the coastal critical habitats including nursery and spawning areas as well as their associated species groups.

The isotopes and biomarker approaches for identifying eroded organic matter sources in sediments: A review

Chapter

Apr 2020
ADV AGRON

Ascertaining the fate of eroded OM is critical for our understanding of the role of soil erosion in global and local carbon cycles on earth's system. In this review, we compiled critical information on isotopes and molecular biomarker approaches that are widely applied to identify sources of eroded OM. We highlight the benefits and shortcomings of each approach and provide a comparison of the different approaches to determine their suitability for application under different environmental conditions and land use. We find that the compound-specific stable isotope signature of biomarkers are superior in their potential to provide plant-specific information on compounds that are likely to be preserved during transport and may at least initially resist diagenetic alterations. Molecular biomarkers provide an ability to reconstruct paleoenvironmental and paleoclimatic conditions due to their capacity to concurrently identify a wide range of sources from a mixture; while stable isotope analyses are also reliable tool to complement the biomarker's limitations for quantifying source identification.

Characteristics and sources of anthropogenic and biogenic hydrocarbons in sediments from the coast of Qatar

Article

Jul 2017

Indicadores Geoquímicos do Aporte de Matéria Orgânica Natural e Antrópica na Área de Influência dos Rios

Chapter

Full-text available

Jul 2018

Lipid biomarkers (steroids, alcohols and taraxerol) were considered to characterize the distribution of organic matter (OM) derived from natural (autochthonous and allochthonous) and anthropogenic (domestic sewage) inputs to surface sediments in the shallow (<50 m) continental shelf along the coast under river influence in SE and AL states, NE Brazil. Surface sediment samples (n = 38) were collected adjacent to rivers São Francisco, Vaza-Barris, Sergipe and Piauí-Real, whose drainage basins have distinct sizes and levels of human settlement. A higher contribution of OM from continental sources to the South of the studied region, particularly nearby rivers Piauí-Real, was revealed by principal component analysis. The São Francisco River, notwithstanding being the largest river in the region, has little contribution of terrestrial OM export to the shelf, probably as a consequence of material retention after the dams constructed along its course. Regarding the input of fecal OM, as indicated by coprostanol, the level of contamination may be considered low. However, the outflow of the small Sergipe and to a lesser extent the Vaza-Barris river are responsible to the export of fecal materials to the shallow shelf, and those regions are no longer pristine.

Lipid biomarkers in suspended particulate matter and surface sediments in the Pearl River Estuary, a subtropical estuary in southern China

Article

Jan 2019

Lipid biomarkers in sediments in the Pearl River Estuary (PRE) have been studied in several previous studies, but little is known about their occurrence in the overlying water. Here, we determined the concentrations of lipids (n-alkanes, n-alkanols, sterols and fatty acids) in suspended particulate matter (SPM) in surface water and in sediments from the PRE. The data will improve our understanding of the sources, transport and sedimentation of lipids in estuarine environments. Our results showed that short-chain (C14-20) n-alkyl lipids contributed more than long-chain (C21-34) n-alkyl lipids to the total lipid concentrations in both SPM and sediments, suggesting aquatic plants and bacteria were the main contributors, whereas terrestrial organic matter (OM) were the minor contributors of n-alkyl lipids. It suggested that phytoplankton and bacteria contributing >65% to the n-alkyl lipids of SPM based on the three end-member mixing models. The concentrations of most lipids, except n-alkanes, decreased quickly in the low-salinity mixing zone and slowly decreased thereafter, with a transient slight increased when the salinity was 20-25, which would have been caused by variations of primary production in the aquatic system. In May, when rainfall was highest, lipids were characterized by a substantial contribution of terrestrial n-alkanes in the upstream SPM. Microbial activity and lipid degradation were found to occur in the water, and were most intense in the low-salinity mixing zone. Terrigenous lipids contributed more to the total lipid concentrations in sediments than in SPM, which demonstrated that terrigenous OM is relatively recalcitrant, and aquatic phytoplankton-derived OM is labile.

Sources of anthropogenic and biogenic hydrocarbons in sediments from the coast of Qatar

Article

Jul 2017

Characteristics and sources of anthropogenic and biogenic hydrocarbon lipids in sediments from the coast of Qatar.

Article

Jul 2017
MAR POLLUT BULL

Surface sediment samples from the coastal zone of Qatar were collected and analyzed to determine the characteristics, and sources of anthropogenic and biogenic hydrocarbons. The main compounds in these surface sediments included n-alkanes, methyl n-alkanoates, diterpenoids, hopanes, steranes, phthalate esters, polycyclic aromatic hydrocarbons (PAHs) and unresolved complex mixture (UCM). Their total concentrations ranged from 18.7±3.7-81.1±7.5 ng/g (3.7±0.6-10.4±4.8%) for n-alkanes, 8.3±2.3-51±3.4 ng/g (3.0±2.0-5.6±2.0%) for methyl n-alkanoates, 1.8±0.1-10.5±1.0 ng/g (1.0±0.5-0.4±0.1%) for diterpenoids, 0.0-79.3±7.4 ng/g (0.0-7.9±0.6%) for hopanes, 0.0-32.9±7.9 ng/g (0.0-6.5±1.0%) for steranes, 0.7±0.1-36.3±3.4 ng/g (0.1±0.1-1.9±3.4%) for phthalates, 0.30±0.2-7.8±0.7 ng/g (0.02±0.04-0.42±0.72%) for PAHs, and 38±9-609±57 ng/g (38.5±13.4-56.5±13.4%) for UCM. The major sources of these lipids were anthropogenic petroleum residues and plasticizers (80-89%), with lesser amounts from natural higher plants and microbial residues (11-20%). Petroleum residues and plasticizer inputs to the coastal sediments of Qatar likely affect the marine ecosystems and associated species groups as well as shallow coastal nursery and spawning areas.

The C32 alkane-1,15-diol as a tracer for riverine input in coastal seas

Article

Dec 2016
GEOCHIM COSMOCHIM AC

Long chain alkyl diols are lipids that occur ubiquitously in marine sediments and are used as a proxy for sea surface temperature (SST), using the Long chain Diol Index (LDI), and for upwelling intensity/high nutrient conditions. The distribution of 1,13- and 1,15-diols has been documented in open marine and lacustrine sediments and suspended particulate matter, but rarely in coastal seas receiving a significant riverine, and thus continental organic matter, input. Here we studied the distribution of diols in four shelf seas with major river outflows: the Gulf of Lion, the Kara Sea, the Amazon shelf and the Berau delta, covering a wide range of climate conditions. The relative abundance of the C32 1,15-diol is consistently higher close to the river mouth and particularly in the suspended particulate matter of the rivers suggesting a terrigenous source. This is supported by statistical analysis which points out a significant positive correlation between the C32 1,15-diol and the Branched and Isoprenoid Tetraether index, a proxy reflecting soil and riverine input in marine environments. However, the C32 1,15-diol was not detected in soils and is unlikely to be derived from vegetation, suggesting that the C32 1,15-diol is mainly produced in rivers. This agrees with the observation that it is a dominant diol in most cultivated freshwater eustigmatophyte algae. We, therefore, suggest that the relative abundance of the C32 1,15-diol can potentially be used as a proxy for riverine organic matter input in shelf seas. Our results also show that long chain alkyl diols delivered by rivers can substantially affect LDI-reconstructed SSTs in coastal regions close to river mouths.

Detection and indication of 1,3,4-C27–29 triol in the sediment of northern South China Sea

Article

Mar 2016

After the detection of the 1,20,21-C29 long-chain triol in some sediments and freshwater pteridophytes, in this study, a new homologous long-chain triol, 1,3,4-C27–29, is detected for the first time in the Site4B core sediment in the northern South China Sea. The hydroxyl location and length of the carbon chain of this newly discovered triol differ from those of 1,20,21-C29 triol. The test results of its molecular distribution and individual carbon isotope reveal that 1,3,4-C29triol has a good correlation with n-C26–30 even carbon-numbered long-chain fatty alcohols, with R 2 (n=68) values of 0.905, 0.929 and 0.903, respectively, and its carbon isotope composition, at–32.3‰±1.9‰, is similar to that of n-C26-30, at–29.13‰±0.87‰,–32.98‰±1.28‰, and–32.98‰±1.28‰. 1,3,4-C29 triol from the Site4B core sediment and terrigenous long-chain fatty alcohol (n-C26–34) show highly consistent distribution trends in the entire section; thus, the former could serve as a proxy indicator of the terrigenous input. Considering that the 1,20,21-C29 triol in previous research belongs to Azolla, which are fresh water pteridophytes, the 1,3,4-C27–29 triol identified in this study might have similar biogenetic derivation. Thus, determination of its biogenic area and growing environment could provide potential organic geochemical evidence supporting the terrigenous input and source in the northern South China Sea.

Characterizing organic matter inputs to sediments of small, intermittent, prairie streams: a molecular marker and stable isotope approach

Article

Oct 2015

Small rivers and streams are ecologically important because they contribute to the export of organic carbon to coastal environments, likely influencing the global carbon cycle. While organic matter (OM) dynamics in large rivers has been studied in quite some detail, less is known about small streams. Sources of OM in streams ultimately determine its availability to the food web and downstream transport. In this study, sediment samples were collected from the King’s Creek watershed in Konza Prairie (Kansas, USA) and analyzed using molecular biomarkers and bulk 13C stable isotopes with the objective to comparatively assess OM inputs between riparian forest vegetation and watershed grassland to small, intermittent streams. We are interested in the potential influence of woody riparian expansion that has been ongoing at the site. Biomarkers typical of the local C4 grasses (branched n-alkanes, phytadienes) were more abundant in some of the sediments of the upper reaches. The sediments of the lower reaches contained biomarkers of algae (short-chain aliphatic compounds, C25:5 highly branched isoprenoid, brassicasterol) and vascular plant-derived material (triterpenols). Degraded OM (triterpene/triterpenol ratio) was found throughout the watershed with no pattern between the upper and lower reaches. Bulk 13C isotope analysis showed that the upper reaches of the watershed receive significant OM inputs from the C4 grasses (74–99 %) while the lower reaches are more strongly influenced by riparian trees (26–27 %) and algae (21–22 %). These results suggest that the environmental dynamics of bulk OM and the biomarker composition of small prairie streams are highly complex and likely a function of several factors such as light availability, riparian vegetative composition and density, and varying degrees of OM storage, retention and transport along the river continuum.

Extraction of climatic signals from fossil organic compounds in marine sediments up to 11.7 Ma old (IODP-U1318)

Article

Apr 2015
ANAL CHIM ACTA

Lipid biomarkers in surface sediments from the Gulf of Genoa, Ligurian sea (NW Mediterranean sea) and their potential for the reconstruction of palaeo-environments

Article

Jul 2014
DEEP-SEA RES PT I

A series of molecular organic markers were determined in surface sediments from the Gulf of Genoa (Ligurian Sea) in order to evaluate their potential for palaeo-environmental reconstructions. Allochthonous input can be characterized by the distributions of n-C29 and n-C31 alkanes, n-C26 and n-C28 alkanols and branched glycerol dialkyl glycerol tetraethers (GDGTs), whose concentrations are generally highest near the river mouths. In the open basin however, terrestrial n-alkanes and n-alkanols may have an additional, aeolian source. Autochthonous input is represented by crenarchaeol and isoprenoid GDGTs. Their concentrations are highest in the open basin showing the preference of Thaumarchaeota for oligotrophic waters. Indications of a significant degradation of sterols and C37 alkenones exclude these lipids as reliable productivity proxies. Using terrestrial and aquatic lipids as end-members allows estimating the percentage of terrestrial organic matter between 20% and 58% in the coastal area decreasing to 1 to 30% in the deep basin. The spatial distribution of sea surface temperature (SST) estimates using the alkenone-based UK’37 index is very similar to the autumnal (November) mean satellite-based SST distribution. Conversely, TEXH86-derived SST estimates are close to winter SSTs in the coastal area and summer SSTs in the open basin. This pattern reflects presumably a shift in the main production of Thaumarchaeota from the coastal area in winter to the open basin in summer. This study represents a major prerequisite for the future application of lipid biomarkers on sediment cores from the Gulf of Genoa.

Occurrence, sources and transport pathways of natural and anthropogenic hydrocarbons in deep-sea sediments of the Eastern Mediterranean Sea

Article

Full-text available

Sep 2013
BG

Surface sediments collected from deep basins (22 stations, 1018-4087 m depth) of the Eastern Mediterranean Sea (EMS) were analyzed for aliphatic, triterpenoid and polycyclic aromatic hydrocarbons (PAHs) as tracers of natural and anthropogenic inputs. Concentrations of total aliphatic hydrocarbons (TAHC), n-alkanes (NA) and the Unresolved Complex Mixture (UCM) of aliphatic hydrocarbons ranged from 1.34 to 49.2 µg g-1, 145 to 4810 ng g-1 and 0.73 to 36.7 µg g-1, respectively, while total PAHs (TPAH25) concentrations ranged from 11.6 to 223 ng g-1. Molecular profiles of aliphatic hydrocarbons and PAHs reflect the contribution of both natural (epicuticular plant waxes) and anthropogenic (degraded petroleum products, unburned fossil fuels and combustion of petroleum, grass, wood and coal) compounds in deep EMS sediments, with hydrocarbon mixtures displaying significant regional variability. Hydrocarbon concentrations correlated significantly with the Total Organic Carbon (TOC) content of sediments, indicating that organic carbon exerts an important control on their transport and fate in the study area, while strong sub-basin and mesoscale variability of water masses also impact their regional characteristics. Major findings of this study support that deep basins/canyons of the EMS could act as traps of both natural and anthropogenic hydrocarbons.

Fatty acid biogeochemistry of sediments from the Chilean coastal upwelling region: Sources and diagenetic changes

Article

May 2006
ORG GEOCHEM

Sediments from two different depositional regions off northern (23°S) and off central Chile (36°S) covering water depths from 126 to 1350m were analysed for their fatty acid (FA) composition. Highest total FA concentrations were found at the shallowest sites from the oxygen minimum zone and total organic carbon (TOC) normalized concentrations were generally higher at 36°S (1.8–4.9mggTOC−1) than at 23°S (0.8–1.6mgg−1 TOC). Reaction rate constants k, calculated from the down-core decrease for total and individual FAs, were 2–4 orders of magnitude higher in the bioturbated sediments off central Chile than for the non-bioturbated ones off northern Chile. Based on the estimated k values, polyunsaturated FAs were the most reactive compounds and long chain saturated n-FAs (LC-FAs) the least reactive. Carbon isotopic compositions of individual LC-FAs (−27.1±1.9‰ vs. VPDB) were similar to those of mid-chain saturated n-FAs (−25.1±1.8‰) and bacterial FAs (−26.1±3.0‰), indicating a non-terrestrial source for most LC-FAs. Principal component analysis (PCA) was applied to reveal information on the main factors that control the FA composition. The first component, explaining 48% of the total variance, was assigned to compositional changes during early diagenesis. Calculated site scores were defined as the FA-Index and showed a good correspondence with other FA based quality indicators and C/N ratios of bulk organic matter. The FA-Index revealed diagenetic alteration that was only partly reflected in the pigment based Chlorin Index and not visible in the amino acid based degradation index.

Sources and fate of amino sugars in coastal Peruvian sediments

Article

May 2006
GEOCHIM COSMOCHIM AC

Amino sugars are involved in the marine carbon and nitrogen cycles and comprise a geochemically significant fraction of marine organic material (OM). However, information on abundance and distribution of these compounds in marine sediments is scarce. Three sediment cores (<50 cm) from the coastal region off Peru were investigated for concentrations of glucosamine (GlcN), galactosamine (GalN), mannosamine (ManN), and muramic acid (Mur). The sum of the four amino sugars accounted for 1.0–2.4% of organic carbon and 1.9–3.8% of nitrogen in the sediments. At the shallowest (102 m) and the deepest site (1278 m), carbon-normalized concentrations decreased down-core, suggesting preferential degradation of amino sugars compared to bulk sedimentary OM. At the site from the center of the oxygen minimum zone (238 m), amino sugar concentrations were high throughout the core, pointing to enhanced preservation of amino sugars under anoxic conditions. GlcN (44–56 mol%) and GalN (33–42 mol%) were the dominant amino sugars in all investigated samples, while ManN (6–14 mol%) and Mur (1–4 mol%) were significantly less abundant. Mur was predominantly associated with cell wall remains rather than with living bacteria, since bacterial abundances estimated based on Mur concentrations were up to 500 times higher than cell counts reported for sediments from this area. GlcN/GalN-ratios (1.1–1.7) indicated that chitin, a polymer of GlcN, was not a major contributor to the amino sugar pool of the investigated sediments. Furthermore, GlcN/Mur-ratios (13–68) are inconsistent with a predominant contribution of intact peptidoglycan, which exhibits a 1:1-ratio. The present study includes a compilation of previously published information on distribution and abundance of amino sugars in the marine environment. Both concentrations and ratios observed in the Peruvian sediments fall in the range of values reported for OM in water column and sediments from different oceanic regions and water depths. Although specific sources for the majority of sedimentary amino sugars remain unidentified, there are indications for a major prokaryotic origin. As suggested in previous studies, the uniform amino sugar compositions of altered marine OM and particularly the close association of GlcN and GalN, which is similar to the ratio observed in living bacteria, are consistent with a transformation of planktonic into bacterial OM.

Even-numbered n-alkanes/n-alkenes predominance in surface sediments of Gabes Gulf in Tunisia

Article

Full-text available

Jul 2009

Hydrocarbons in surface sediments were studied quantitatively and qualitatively in 18 stations along the coastline of Gabes Gulf in Tunisia. The results show that the total hydrocarbon levels vary along a wide range from 90 to 1,800ppm. The GC–MS profiles of aliphatic hydrocarbons vary according to the stations and show that the hydrocarbons were derived from various sources. A special feature prevalent in several stations was identified: aliphatic hydrocarbons with distinctive chemical features. This includes a high abundance of even-numbered n-alkanes (n-C14–n-C26, maximizing at n-C18, n-C20 and n-C22) and n-alk-1-enes (n-C14:1–n-C24:1, maximizing at n-C16:1, n-C18:1, n-C20:1 and n-C22:1). This unusual predominance of even-numbered n-alkanes/alkenes is reported for the first time in the Gulf of Gabes and it thus contributes to the information on the rare occurrence of such distributions in the geosphere. KeywordsEven n-alkanes-Even n-alkenes-Surface sediment-Gulf of Gabes

Hydroxyl radical-induced photochemical formation of dicarboxylic acids from unsaturated fatty acid (oleic cid) in aqueous solution

Article

Apr 2007
J PHOTOCH PHOTOBIO A

In this study, we assess under laboratory controlled conditions the direct and hydroxyl radical (OH)-induced photochemical production of low molecular weight (LMW) dicarboxylic acids and related compounds (C2–C9) (DCAs) from oleic acid (cis-9-octadecenoic, Δ9C18) in aqueous solution. Nitrate (NO3−)-amended and unamended oleate solutions were irradiated under ultraviolet-B radiation (UV-B, 313 nm) for 5 h, with NO3− being the source of OH. The OH-induced photochemical production of DCAs (C2di–C9di) (170 ± 26 nM h−1) was much higher than that induced by the direct effect of UV-B (33 ± 22 nM h−1), accounting for approximately 85% of the total (direct + OH-induced) photochemical production of DCAs (C2di–C9di) (198 ± 15 nM h−1). Azelaic acid (C9di) was the dominant photoproduct (comprising 63 and 44% of DCAs in the direct and OH-induced photochemical production, respectively) followed by C8di, C7di and C6di, whereas shorter chain compounds (C2di–C5di) were minor produced species. Using our estimate of OH photoproduction (P-OH in nM h−1), the production of C9di from 50 μM of oleic acid was evaluated at ∼45 nM (nM OH)−1.

The Chlorin-Index: A new parameter for organic matter freshness in sediments

Article

Full-text available

Mar 2005
GEOCHEM GEOPHY GEOSY

(1) Total chlorins, comprising degradation products of chlorophyll, have been used recently to reconstruct paleoproductivity from marine sediment cores. Here, we report on a new index, the Chlorin Index (CI), that proves to be a helpful tool for rapidly estimating organic matter freshness in marine sediments. The CI is a ratio between the fluorescence intensity of a sediment extracted with acetone and treated with hydrochloric acid and the original sediment extract. It represents the ratio of chlorophyll and its degradation products deposited in the sediments that could still be chemically transformed and those that are inert to chemical attack. The ratio is lower in sediments that include freshly deposited phytoplankton material and higher in older, more degraded sediments. We measured this new parameter on surface sediments, and sediments from several short and a long sediment core from different oceanic settings. CI values range from 0.2 for chlorophyll a to 0.36-0.56 for fresh material deposited on the shelf off Namibia to values around 0.67 in sediments off Chile and Peru to values up to 0.97 for sediments in a deep core from the northeastern slope of the Arabian Sea. We have compared the CI to rates of bacterial sulfate reduction, as a direct measure of organic matter reactivity and to other degradation indices based on amino acid composition. We conclude that the CI is a reliable and simple tool for the characterization of organic material freshness in sediments in respect to its degradation state.

Natural and anthropogenic sources of extractable organic matter in sediments from the coastal zone of the Arabian Gulf in Saudi Arabia.

Article

Full-text available

Dec 2021

Production of short-chain n-fatty acids in coral reefs in the southern South China Sea since the Late Miocene

Article

Feb 2022
PALAEOGEOGR PALAEOCL

The monsoon system modulates surface production in the South China Sea (SCS). The winter monsoon has long been recognized as the primary factor regulating surface production in the northern SCS; however, the role of monsoon remains in debate in the southern SCS. Here, we present a long record of short-chain n-fatty acids (n-FAs) in reefal carbonates from one deep well (NK1) on an isolated coral atoll (Meiji) in order to provide new insights into the change of surface production in the southern SCS since the Late Miocene (ca. 10.5 Ma). Short-chain n-FAs indicative of total marine organic matter input are rather feasible to reflect the total production associated with mixotrophic reef-building corals that feed on various marine biotas (i.e., phytoplankton, zooplankton and bacteria). By ruling out the significant influence of diagenetic and degradation processes, short-chain n-FAs can be further applied to reconstruct paleo-production in Well NK1 coral reefs. The temporal distribution of short-chain n-FAs changes similarly with many other independent paleo-production records (i.e., Ln(Ba/Ti) and opal) in Well NK1 and adjacent ODP Site 1143, demonstrating the close coupling between coral reef production and surface water production. This occurs through the common factor of nutrients in modulating production of symbiotic autotrophic coralgae and asymbiotic phytoplankton and/or the large heterotrophic dependence of corals on phytoplankton-governed food webs in surface waters. Short-chain n-FAs inferred surface production displays a progressively decreased trend from the Late Miocene to Pliocene (ca. 10.5–2.6 Ma) followed by a substantial increase since the Pleistocene on million-year timescales, which follows the variation of terrigenous supply to the coral atoll and responds almost inversely to the sea-level change. Accordingly, we propose that long-term paleo-production in the southern SCS was associated with terrestrial nutrient input which was controlled by relative sea-level change since the Late Miocene. This study highlights the feasibility of short-chain n-FAs as appropriate production recorders in shallow-water coral reefs which are widespread in tropical-subtropical oceans, providing valuable perspectives on long-term paleo-production evolution in surface waters.

Natural and anthropogenic sources of extractable organic matter in sediments from the coastal zone of the Arabian Gulf in Saudi Arabia

Preprint

Full-text available

Dec 2021

Surface sediment samples from the Arabian Gulf coast of Saudi Arabia were collected by Van Veen grab sampler to identify the characteristics, distribution, levels, and to discriminate between natural and anthropogenic sources of the total extractable organic matter (TEOM). The dried and sieved sediments were extracted with a dichloromethane/methanol mixture for analysis by gas chromatography-mass spectrometry. The TEOM included n-alkanes (353.9±283.8 ng.g ⁻¹ ), n-alkanols (283.2±296.1 ng.g ⁻¹ ), fatty acid methyl esters (245.2±353.7 ng.g ⁻¹ ), hopanes (100.7±158.2 ng.g ⁻¹ ), steranes (58.5±96.3 ng.g ⁻¹ ), triterpenoids (18.9±21.1 ng.g ⁻¹ ), steroids (15.3±17.0 ng.g ⁻¹ ), polycyclic aromatic hydrocarbons (PAHs) (0.48±1.19 ng.g ⁻¹ ), as well as an unresolved complex mixture (UCM =1633±3151 ng.g ⁻¹ ) and petrochemicals (343.1±424.2 ng.g ⁻¹ ). The major sources of these TEOM compound groups were anthropogenic (petroleum and petrochemical) and natural (lipids from higher plants, marine material, and microbiota) inputs. Anthropogenic contaminants from petroleum products ranged from 46.6-85.6% of the TEOM, whereas petrochemicals varied from 10.7-40.6%. Biogenic influx from terrestrial vegetation ranged from 5.7-19.3%, and marine biotic sources varied from 11.1-37.5%. The continuous accumulation of anthropogenic contaminants will ultimately affect the critical habitats of this marine coastal region. This provides a basis for further studies to understand human and developmental activities on delivery, deposition processes, distribution, and biogeochemical alteration of organic matter in the coastal zones of the Arabian Gulf. Such studies are important for sustainable development and protection of these key regional habitats.

Long-chain diols in rivers: Distribution and potential biological sources

Article

Full-text available

Jul 2018

Long-chain diols (LCDs) occur widespread in marine environments and also in lakes and rivers. Transport of LCDs from rivers may impact the distribution of LCDs in coastal environments, however relatively little is known about the distribution and biological sources of LCDs in river systems. In this study, we investigated the distribution of LCDs in suspended particulate matter (SPM) of three river systems (Godavari, Danube, and Rhine) in relation with precipitation, temperature, and source catchments. The dominant long-chain diol is the C32 1,15-diol followed by the C30 1,15-diol in all studied river systems. In regions influenced by marine waters, such as delta systems, the fractional abundance of the C30 1,15-diol is substantially higher than in the river itself, suggesting different LCD producers in marine and freshwater environments. A change in the LCD distribution along the downstream transects of the rivers studied was not observed. However, an effect of river flow is observed; i.e., the concentration of the C32 1,15-diol is higher in stagnant waters such as reservoirs and during seasons with river low stands. A seasonal change in the LCD distribution was observed in the Rhine, likely due to a change in the producers. Eukaryotic diversity analysis by 18S rRNA gene sequencing of SPM from the Rhine showed extremely low abundances of sequences (i.e., < 0.32 % of total reads) related to known algal LCD producers. Furthermore, incubation of the river water with 13C-labeled bicarbonate did not result in 13C incorporation into LCDs. This indicates that the LCDs present are mainly of fossil origin in the fast-flowing part of the Rhine. Overall, our results suggest that the LCD producers in rivers predominantly reside in lakes or side ponds that are part of the river system.

The C32 alkane-1,15-diol as a proxy of late Quaternary riverine input in coastal margins

Article

Full-text available

Aug 2017
CLIM PAST

The study of past sedimentary records from coastal margins allows us to reconstruct variations in terrestrial input into the marine realm and to gain insight into continental climatic variability. There are numerous organic proxies for tracing terrestrial input into marine environments but none that strictly reflect the input of river-produced organic matter. Here, we test the fractional abundance of the C32 alkane 1,15-diol relative to all 1,13- and 1,15-long-chain diols (FC32 1, 15) as a tracer of input of river-produced organic matter in the marine realm in surface and Quaternary (0–45 ka) sediments on the shelf off the Zambezi and nearby smaller rivers in the Mozambique Channel (western Indian Ocean). A Quaternary (0–22 ka) sediment record off the Nile River mouth in the eastern Mediterranean was also studied for long-chain diols. For the Mozambique Channel, surface sediments of sites most proximal to Mozambique rivers showed the highest F1, 15 − C32 (up to 10 %). The sedimentary record shows high (15–35 %) pre-Holocene F1, 15 − C32 and low (< 10 %) Holocene F1, 15 − C32 values, with a major decrease between 18 and 12 ka. F1, 15 − C32 is significantly correlated (r2 = 0.83, p < 0.001) with the branched and isoprenoid tetraether (BIT) index, a proxy for the input of soil and river-produced organic matter in the marine environment, which declines from 0.25 to 0.60 for the pre-Holocene to < 0.10 for the Holocene. This decrease in both FC32 1, 15 and the BIT is interpreted to be mainly due to rising sea level, which caused the Zambezi River mouth to become more distal to our study site, thereby decreasing riverine input at the core location. Some small discrepancies are observed between the records of the BIT index and FC32 1, 15 for Heinrich Event 1 (H1) and the Younger Dryas (YD), which may be explained by a change in soil sources in the catchment area rather than a change in river influx. Like for the Mozambique Channel, a significant correlation between FC32 1, 15 and the BIT index (r2 = 0.38, p < 0.001) is observed for the eastern Mediterranean Nile record. Here also, the BIT index and FC32 1, 15 are lower in the Holocene than in the pre-Holocene, which is likely due to the sea level rise. In general, the differences between the BIT index and FC32 1, 15 eastern Mediterranean Nile records can be explained by the fact that the BIT index is not only affected by riverine runoff but also by vegetation cover with increasing cover leading to lower soil erosion. Our results confirm that FC32 1, 15 is a complementary proxy for tracing riverine input of organic matter into marine shelf settings, and, in comparison with other proxies, it seems not to be affected by soil and vegetation changes in the catchment area.

Geoquímica orgànica ambiental de sistemes aquàtics a Catalunya

Chapter

Full-text available

Dec 2016

F. Xavier C. de las Heras

In this paper, we present four water systems, two freshwater sediments belonging to artificial lakes coming from Castelldefels and Manresa. Also two sediments belonging to saline environments, e.g: streams such as Horta d’Avinyó and Ribera Salada from Cambrils (Odèn). In order to study thoroughly these sediments geochemical organic soluble organic fraction was analysed. It consists mostly of lipids from natural sources, but also from an anthropogenic origin. The used technique was gas chromatography coupled to mass spectrometry (GC-MS). In each of the four studied water systems biomarkers have been identified in order to assign them to autochtonous natural inputs such as algae or bacteria (in salty environments are biomarkers of extremophile bacteria) or allochtonous higher plants. In this sense, we have also identified anthropogenic contributions, such as inputs from faecal contaminants or petrogenic pollutants coming directly from fossil fuels or their combustion products.

Composition and sources of sedimentary organic matter in the deep eastern Mediterranean Sea

Article

Full-text available

Dec 2015
BG

Surface sediments collected from deep slopes and basins (1018–4087 m depth) of the oligotrophic eastern Mediterranean Sea have been analysed for bulk elemental and isotopic composition of organic carbon, total nitrogen and selected lipid biomarkers, jointly with grain size distribution and other geochemical proxies. The distribution and sources of sedimentary organic matter (OM) have been subsequently assessed and general environmental variables, such as water column depth and physical circulation patterns, have been examined as causative factors of deep-sea sediment characteristics. Lithogenic and biogenic carbonates are the dominant sedimentary fractions, accounting for up to 85.4 and 66.5 % of the total weight respectively. The low OC and TN contents in the surface sediments of the study area, which ranged from 0.15 to 1.15 % and 0.06 to 0.11 % respectively, reflect the oligotrophic character of the eastern Mediterranean Sea. Both bulk and molecular organic tracers reflect a mixed contribution from autochthonous and allochthonous sources for the sedimentary OM, as indicated by relatively degraded marine OM, terrestrial plant waxes and anthropogenic OM (e.g. degraded petroleum by-products) respectively. Wide regional variations have been observed amongst the studied proxies, which reflect the multiple factors controlling sedimentation in the deep eastern Mediterranean Sea. Our findings highlight the role of deep eastern Mediterranean basins as depocentres of organic-rich fine-grained sediments (mean 5.4 ± 2.4 μm), with OM accumulation and burial being attributed to aggregation mechanisms and hydrodynamic sorting. A multi-proxy approach is applied aiming to investigate the biogeochemical composition of sediment samples, which sheds new light on the sources and transport mechanisms along with the impact of preservation vs. diagenetic processes on the composition of sedimentary OM in the deep basins of the oligotrophic eastern Mediterranean Sea.

Composition and sources of sedimentary organic matter in deep basins of the North-Eastern Mediterranean Sea

Article

Full-text available

Jul 2015
BGD

Surface sediments collected from deep slopes and basins (1018–4087 m depth) of the oligotrophic Eastern Mediterranean Sea have been analysed for bulk elemental and isotopic composition of organic carbon, total nitrogen and selected lipid biomarkers, jointly with grain size distribution and other geochemical proxies. The distribution and sources of sedimentary organic matter (OM) have been subsequently assessed and general environmental variables, such as water depth and currents, have been examined as causative factors of deep-sea sediment characteristics. Lithogenic and biogenic carbonates are the dominant sedimentary fractions, while both bulk and molecular organic tracers reflect a mixed contribution from autochthonous and allochthonous sources for the sedimentary OM, as indicated by relatively degraded marine OM, terrestrial plant waxes and anthropogenic OM including degraded petroleum by-products, respectively. Wide regional variations have been observed amongst the studied proxies, which reflect the multiple factors controlling sedimentation in the deep Eastern Mediterranean Sea. Our findings highlight the role of deep Eastern Mediterranean basins as depocentres of organic-rich fine-grained sediments (mean 5.4 ± 2.4 μm), with OM accumulation and burial due to aggregation mechanisms and hydrodynamic sorting. A multi-proxy approach is hired to investigate the biogeochemical composition of sediment samples, which sheds new light on the sources and transport mechanisms along with the impact of preservation vs. diagenetic processes on the composition of sedimentary OM in the deep basins of the oligotrophic Eastern Mediterranean Sea.

A review of environmental characteristics and effects of low-molecular weight organic acids in the surface ecosystem

Article

May 2014
J ENVIRON SCI-CHINA

Low molecular weight organic acids (LMWOAs) are prevalent on the earth's surface. They are vital intermediate products during metabolic pathways of organic matter and participate in the tricarboxylic acid cycle during life activities. Photochemical reactions are pivotal for LMWOAs' origination and play a large role in determining their diversity and their ultimate fate. Within the long time that organic matter is preserved in sediments, it can be decomposed and converted to release organic and inorganic pollutants as well as C, N, and P nutrients, which are of potential ecological risk in causing secondary pollution to lake water. The sediment pool is a comprehensive and complex compartment closely associated with overlying water by various biochemical processes, during which LMWOAs play critical roles to transport and transform elements. This article elucidates geochemical behaviors of LMWOAs in the surface environment in details, taking natural water, soil, and aerosol as examples, focusing on reviewing research developments on sources and characteristics, migration and mineralization of LMWOAs and relevant environmental effects. Simultaneously, this review article depicts the categories and contents of LMWOAs or their contribution to DOC in environmental media, and evaluates their importance during organic matter early diagenesis. Through concluding and discussing the conversion mechanisms and influencing factors, the next research orientations on LMWOAs in lake ecosystems are determined, mainly concerning relationships with hydrochemical parameters and microorganisms, and interactions with pollutants. This will enrich the knowledge on organic matter degradation and related environmental effects, and help reconstruct a theoretical framework for organic compound succession and influencing factors, providing basic data for lake eutrophication and ecological risk assessment, conducive to better control over water pollution and proper management of water quality.

A new regional, mid-Holocene palaeoprecipitation signal of the Asian Summer Monsoon

Article

Oct 2013
QUATERNARY SCI REV

The Dongge Cave speleothem δ18O record, which lies in the Pearl River basin (China), has been interpreted as recording a regional decline in Asian Summer Monsoon precipitation over the last 6.5 ka. The same overall trend is seen in the bulk sedimentary organic δ13Corg record from a core in the Pearl River Estuary. However, the two records differ in detail and the regional nature of the Dongge palaeoprecipitation signal has therefore been questioned. Our study re-evaluates both records by constructing, for the same estuarine core, biomarker and compound-specific δ13C records, which have better constrained terrestrial and marine end members than δ13Corg, providing additional insights into the evolution of the Asian Summer Monsoon.

Organic matter distribution in the modern sediments of the Pearl River Estuary

Article

Aug 2012
ORG GEOCHEM

We determined biomarker concentrations and distributions for surface sediments from 54 sites in the Pearl River Estuary, China. We focus on a suite of four biomarker-based indicators for relative terrestrial to marine organic matter (OM) source: the branched-isoprenoid tetraether (BIT) index, the ratio of high/low molecular weight n-alcohols [(ΣC26–34/(ΣC16+18 + ΣC26–34)], an analogous ratio for n-fatty acids and the ΣC29-steroids/(ΣC29-steroids + brassicasterol) ratio. All four exhibit the same terrestrial to marine transition seen in previous bulk δ13C studies, but with an abrupt decrease in the relative terrestrial contribution across the delta front to pro-delta transition. Concentrations of terrestrially-derived biomarkers show no systematic decrease across the transition. Instead, the decrease in the proportion of terrestrial OM is due to a decrease in the sedimentation rate and associated terrestrial OM burial across the delta toe. This suggests that diagenetic controls on the fate of terrestrial OM, such as increased biodegradation where sedimentation rate is low, are subordinate to sedimentological processes. Biomarker-derived temperature values are cooler than expected for the lower Pearl River catchment, suggesting that the dominant component of the terrestrial OM is derived from the cooler upland regions of the catchment. The dominance of input from more distal terrain with greater topographic relief is evidence for the importance of geomorphological control on terrigenous OM transport. Collectively, the results demonstrate the importance of sedimentological processes in the supply, deposition and transport of terrestrial OM.

Fatty acid content and composition of sediments from Siberian eutrophic water bodies: Implications for biodiesel production

Article

Mar 2013

We studied lipids and fatty acids (FA) in bottom sediments from four Siberian water bodies, Bugach, Lesnoi and Krasnoyarsk freshwater reservoirs and brackish Shira lake, that differed in physico-chemical and biological conditions. We considered the potential of the bottom sediments as a feedstock for biodiesel production and estimated properties of the obtained biodiesel as a fuel on the basis of FA composition. Contents of lipids and FA in the sediments moderately varied and were generally close to the reported data from lacustrine and estuarine systems. We confirmed that long-term eutrophication of a water body resulted in the lipid-rich bottom sediments that make them a feedstock for biodiesel production. Each of the studied water bodies had specific FA composition of sediments likely due to different organic matter sources and transformation processes. Despite these differences in FA profiles, calculated key parameters (cetane number, iodine number and heat of combustion) of biodiesel produced from all the studied sediments met the limits established by current biodiesel standards. Thus, the variation in the sediment FA composition due to environmental characteristics of a water body likely has no principal significance for fuel properties of the obtained biodiesel.

Inorganic Carbon of Sediments in the Yangtze River Estuary and Jiaozhou Bay

Article

Feb 2006

JGOFS results showed that the ocean is a major sink for the increasing atmospheric carbon dioxide resulting from human activity. However, the role of the coastal seas in the global carbon cycling is poorly understood. In the present work, the inorganic carbon (IC) in the Yangtze River Estuary and Jiaozhou Bay are studied as examples of offshore sediments. Sequential extraction was used to divide inorganic carbon in the sediments into five forms, NaCl form, NH3 H2O form, NaOH form, NH2OH HCl form and HCl form. Studied of their content and influencing factors were also showed that NaCl form < NH3 H2O form<NaOH form < NH2OH HCl form<HCl form, and that their influencing factors of pH, Eh, Es, water content, organic carbon, organic nitrogen, inorganic nitrogen, organic phosphorus and inorganic phosphorus on inorganic carbon can be divided into two groups, and that every factor has different influence on different form or on the same form in different environment. Different IC form may transform into each other in the early diagenetic process of sediment, but NaCl form, NH3 H2O form, NaOH form and NH2OH HCl form may convert to HCl form ultimately. So every IC form has different contribution to carbon cycling. This study showed that the contribution of various form of IC to the carbon cycle is in the order of NaOH form>NH2OH HCl form>NH3 H2O form>NaCl form>HCl form, and that the contribution of HCl form contributes little to carbon cycling, HCl form may be one of end-result of atmospheric CO2. So Yangtze River estuary sediment may absorb at least about 40.96×1011g atmospheric CO2 every year, which indicated that offshore sediment play an important role in absorbing atmospheric CO2.

Study of the mineralization effect on the distribution of lipids in sediments from the Cretan Sea: Evidence for hydrocarbon degradation and starvation stress

Article

Nov 2005
CONT SHELF RES

Sedimentary diagenetic processes alter the composition and distribution of different lipid compounds. In the present study alterations mediated by microbial communities were investigated along a bathymetric gradient (100 m at 35°23′N–25°09′E, 617 m at 35°33′N–25°08′E, 1494 m at 35°44′N–25°08′E) over the continental margin of northern Crete (Greece, Eastern Mediterranean Sea). Bacterial abundances and distribution were studied using phospholipid linked fatty acids (PLFA), in the range of C8–C22, released from intact phospholipids. Lipid components (aliphatic hydrocarbons, free fatty acids, glycerides and glycolipids) were studied over a 2-month incubation period. Carbon mineralization rates at all stations indicated an uneven distribution of active aerobic bacteria with values decreasing towards the deeper stations. PLFA homologue profiles denoted that aerobic gram negative and sulfur oxidizing bacteria dominated microbial communities while the anaerobic, gram positive and sulfate reducing bacteria occurred only in traces. The n-alkane (NA) composition revealed a strong predominance of homologues with odd carbon numbers suggesting an important terrestrial contribution to the sediments. The estimated descriptive ratios of NA, the sum of short chain NA (C15–C20) and long chain NA (C21–C36) to 17α(H),21β(H)-C30-hopane, before and after a two-month incubation period, indicated the occurrence of hydrocarbon degradation processes. Increased ratios of saturated to unsaturated fatty acids were also recorded after the incubation indicating the starvation of bacterial communities by the end of the experiments.

Occurrence and distribution of hydrocarbons in surface sediments from Marseille Bay (France)

Article

Aug 2009
MAR POLLUT BULL

Production, Transport, and Alteration of Particulate Organic Matter in the Marine Water Column

Chapter

Full-text available

Jan 1993

Most of the organic matter sequestered in Recent and ancient marine sediments is ultimately derived from organic matter biosynthesized by marine organisms inhabiting the surface waters of the oceans and transported to the seafloor as particulate organic matter (POM). However, most of the organic matter produced in the upper ocean is recycled in the upper few hundred meters of the water column (the epipelagic zone). Only a small fraction of the particulate material produced in the euphotic zone sinks into deeper waters (the mesopelagic and bathypelagic zones). In turn, only a small fraction of this sinking material survives transport to the seafloor to be preserved in the sediments. Extensive alteration of organic matter in the water column and at the sediment-water interface can yield sedimentary organic matter having a chemical composition markedly different from that of the material originally biosynthesized. A major goal of marine organic geochemists is to understand the qualitative and quantitative changes which occur in the water column and at the sediment-water interface (Wakeham and Lee, 1989). In this chapter we will discuss recent advances in our understanding of water column processes which influence the cycling of organic matter in the ocean.

The use of sediment traps to determine sterol sources in coastal sediments off Peru

Article

Full-text available

Jan 1983

Gagosian, R.B., Volkman, J.K. and Nigrelli, G.E. (1983). The use of sediment traps to determine sterol sources in coastal sediments off Peru. In Advances in Organic Geochemistry, 1981. (eds Bjoroy M. et al.) pp. 369-379. Wiley, Chichester.

The productive and optical status of the oligotrophic waters of the Southern Aegean Sea (Cretan Sea), Eastern Mediterranean

Article

Full-text available

May 1998

L. Ignatiades

Primary production, pigment concentrations and spectral measurements of downwelling irradiance were made at four stations in four seasons (spring, summer, autumn, winter) during 1994 in the waters of the South Aegean Sea (Cretan Sea), Eastern Mediterranean. Rates of production were determined using in Situ incubation techniques and included measurements at the surface microlayer. Depth-integrated values averaged over season were 5.66 mg C m−2 h−1 for primary production and the corresponding chlorophyll (Ch1) a and phaeophytin (Phaeo) a values had means of 4.87 and 1.21 mg m−3 respectively. The assimilation ratio remained very low (mean over season: 1.19 mg C mg−2 Chl a h−1 as did the Phaeo a/Chl a ratio (mean over season: 0.24). The annual production for the area was estimated to yield 24.79 g C m−2 year−1. Primary production and Chl a estimates showed statistically significant seasonal, spatial and depth variations. The spectral values of the attenuation coefficient Kd (λ) at 480 nm in the water column 0-50 m varied seasonally with higher values in spring (average 0.043 m−1) and winter (average 0.056 m−1, and lower values in summer (average 0.035 m−1 and autumn (average 0.026 m−1). The overall mean of this coefficient was 0.040 m−1 thus classifying the waters of the South Aegean Sea as Jerlov's Optical Type I. The results of the present investigation based on the productivity and light attenuation data demonstrate clearly that the South Aegean can be considered as one of the most oligotrophic areas of the Mediterranean Sea.

Rates and mechanisms of fatty acid degradation in oxic and anoxic coastal marine sediments of Long Island Sound, New York, USA

Article

Full-text available

Jan 1997
GEOCHIM COSMOCHIM AC

The rates and pathways of labile organic matter degradation significantly affect the cycling of organic carbon and nutrients in coastal sediments. In this study, we measured degradation rate constants of saturated and unsaturated fatty acids by incubating radiolabeled 1-14C-palmitic (16:0) and 1-14C-oleic (18:1) acids and an unlabeled plankton mixture in oxic and anoxic sediments from Long Island Sound (LIS) under laboratory-controlled conditions. Rate constants for degradation of 16:0 and 18:1 fatty acids were higher in oxic sediments than in anoxic sediments. Degradation of the unsaturated 18:1 acid in anoxic sediments was two times faster than for 16:0, while there was little difference between the two fatty acids in oxic sediments. The incubation results clearly showed that fatty acids degrade through multiple pathways in both oxic and anoxic sediments. About 80–90% of the label was lost from the incubated sediments (presumably as14CO2 or other volatile products), and 5–10% was incorporated into the sediment matrix. Both degradation and incorporation into the sediment matrix were slightly greater under oxic conditions. A small part (5–10%) of the label was incorporated into what are presumed to be metabolic products. A higher percentage of this incorporation occurred under anoxic conditions, implying that anaerobic bacteria are less efficient at degrading the labeled fatty acid to volatile products such as CO2. In the oxic sediments, more oleic than palmitic acid was converted into intermediate metabolites, indicating that the unsaturated fatty acid was degraded less efficiently. There was little difference in formation of metabolites between oleic and palmitic acids under anoxic conditions. The seasonal distributions of palmitic and oleic acids at two coastal LIS sites with distinctive oxygen content were modeled to yield degradation rate constants for these two fatty acids. The comparison between fatty acid degradation rate constants derived from incubation experiments and field profiles is consistent with anaerobic degradation being predominant in LIS sediments.

Lipid biomarkers of the Haptophyta

Article

Full-text available

Jan 1994

Conte, M.H., Volkman, J.K. and Eglinton, G. (1994). Lipid biomarkers of the Haptophyta. In The Haptophyte Algae (eds J.C. Green and B.S.C. Leadbeater), pp. 351-377. Clarendon Press, Oxford.

Algal and fungal waxes

Article

Full-text available

Jan 1976

John Weete

Composition and transport of lipid biomarkers through the water column and surficial sediments of the equatorial Pacific Ocean

Article

Full-text available

Dec 1997
DEEP-SEA RES PT II

A systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the U.S. JGOFS EgPac transect from l2°N to l5°S at 140°W. Fluxes of lipids out of the euphotic zone varied spatially and temporally, ranging from ≈0.20 0.6 mmol lipid-C m-2 day-1. Lipid fluxes were greatly attenuated with increasing water column depth, dropping to 0.002-0.06 mmol lipid-C m-2 day-1 in deep-water sediment traps. Sediment accumulation rates for lipids were ≈ 0.0002 0.00003 mmol lipid-C m-2 day-1. Lipids comprised ≈ 11 23% of Corg in net-plankton, 10 30% in particles exiting the euphotic zone, 2 4% particles in the deep EgPac, and 0.1-1 % in sediments. Lipids were, in general, selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment. Qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branchedchain C15 and C17 fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment, indicating inputs of organic matter from bacteria. Long-chain C39 alkenones of marine origin and long-chain C20-C30 fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is, thus, essential for using the sediment record for reconstructing past oceanic environments.

Organic matter composition of the continental shelf and bathyal sediments of the Cretan Sea (NE Mediterranean)

Article

Full-text available

Aug 2000
PROG OCEANOGR

The seasonal, spatial and bathymetric changes in the distribution of chloroplastic pigments (Chl a, phaeopigments and CPE), TOC, TON, ATP, bottom water nutrient content and the main biochemical classes of organic compounds (lipids, proteins and carbohydrates) were recorded from May 1994 to September 1995 over the continental margin of northern Crete. The concentration of chloroplastic pigment equivalents (CPE) was always low, dropping dramatically along the shelf-slope gradient. Microbial activity (ATP) also dropped sharply beyond the continental shelf following a distribution pattern similar to TOC and TON. Lipid, protein and carbohydrate concentrations, as well as biopolymeric carbon were comparable to those reported for other more productive areas, however, the quality of the organic matter itself was rather poor. Thus, carbohydrates, the dominant biochemical class, were characterised by being highly (80–99%) refractory, as soluble carbohydrates represented (on annual average) only 6% of the total carbohydrate pool. Protein and lipid concentrations strongly decreased with depth, indicating depletion of trophic resources in the bathyal zone. Proteins appeared to be the more degradable compounds and indeed the protein to carbohydrate ratios were found to decrease strongly in the deeper stations. Organic matter content and quality decreased both with increasing distance from the coast and within the sediment. All sedimentary organic compounds were found to vary between sampling periods, with the changes being more pronounced over the continental shelf. The different temporal patterns of the various components suggest a different composition and/or origin of the OM inputs during the different sampling periods. The amount of material reaching the sediments below 540 m is extremely low, suggesting that most of the organic material is decomposed and/or utilised before reaching the sea floor. In conclusion, the continental shelf and bathyal sediments of the Cretan Sea can be considered, from a trophic point of view, as two different subsystems.

Sorptive preservation of labile organic matter in marine sediments

Article

Full-text available

Jan 1994
NATURE

Changes in the lipid composition of Antarctic sea-ice diatom communities during a spring bloom: an indication of community physiological status

Article

Full-text available

Jun 1989
ANTARCT SCI

The lipid composition of natural populations of diatoms in the sea ice at McMurdo Sound was determined during the austral spring bloom of 1985, using an Iatroscan TLC-FID system. The major lipid classes in all samples were polar lipids (including phospholipid, glycolipid and chlorophyll) and triacylglycerol, with lesser proportions of free fatty acids. Total lipid increased through November and early December, reaching a maximum (3300 mg mZ at Cape Armitage and 1800 mg m-2 at Erebus Ice Tongue) c. one week after the chlorophyll a maxima. This increase was largely attributable to a corresponding increase in triacylglycerol. At the lipid maxima, uiacylglycerol/polar lipid ratios in the range 1 .O to 2.5 were observed. The dynamic variations in lipid class abundances indicate that profound changes in the physiology of sea- ice diatoms are occurring throughout the spring bloom. A range of sterols (CX-C3J were detected; 24- methylenecholesterol, brassicasterol and 24-ethylcholesterol were the major sterols at the Cape Armitage and Erebus sites. The similarity of the sterol profiles to those of Antarctic freshwater algal communities strongly indicates diatoms as a more probable source of C, sterols in the freshwater lakes than cyanobacteria or other algal groups. The hydrocarbons isolated from sea-ice diatoms at all sites were dominated by two unsaturated components, n-C,,:, and a diunsaturated isoprenoid C, alkene. Until this study, no biological source had been validated for the isoprenoid Cz:2 diene, even though it has been detected in many estuarine and coastal sediments.

Production of acyclic isoprenoid compounds during the photodegradation of chlorophyll-a in seawater

Article

Full-text available

Jul 1991
J PHOTOCH PHOTOBIO A

A suspension of chlorophyll-a in synthetic seawater was irradiated with solar light until bleaching. After irradiation, methyl ethyl maleimide and several isoprenoid photoproducts were identified by gas chromatography and gas chromatography/mass spectrometry analyses. In order to explain the formation of these isoprenoid compounds, various mechanisms involving the initial addition of singlet oxygen on the double bond of the chlorophyll-a phytyl chain were proposed. The photosensitized oxidation of phytyl propionate in the presence of haematoporphyrin confirmed these mechanisms.

Modifications of the C 37 alkenone and alkenoate composition in the water column and sediment: Possible implications for sea surface temperature estimates in paleoceanography

Article

Full-text available

Nov 2000
GEOCHEM GEOPHY GEOSY

The literature pertaining to C37 alkenone and C37 and C38 alkenoate production and diagenesis has been reviewed and evaluated for issues that might jeopardize their usefulness in paleotemperature estimation. We also examined the use of the C37 alkenones as paleoproductivity indicators, the stability of their δ13C isotopic compositions, and their incorporation into the nonsolvent extractable organic matter fraction. Biological transformation of organic matter by bacteria and zooplankton does not appear to cause significant changes to the ratio of C37:2 and C37:3 alkenones, but there are major alterations in the relative composition of alkenoates. Studies of water column processes and postdepositional sedimentary changes indicate overall stability in the C37:2/(C37:2 + C37:3) ratio, leading to effective preservation of the paleotemperature signal. This is not the case for alkenoates, and there also appear to be some doubts about the dependence between sea surface temperature and the sedimentary abundance of the C37:4 alkenone. C37 alkenones may provide useful qualitative estimates of marine paleoproductivity. Although these compounds are apparently only derived from Haptophycea, changes in their quantitative composition might reflect changes in nutrient availability that on sedimentary timescales should also be generally significant of other algal species. One caveat is that in highly productive upwelling systems, productivity may be expressed mostly in diatom growth and thus not measurable by the C37 alkenones. No changes in δ13C C37 alkenone composition are observed upon zooplankton ingestion. Although this is expected from a theoretical perspective, further studies are encouraged in order to fully assess the stability of the isotopic signal during C37 alkenone diagenesis. Finally, alkenones bound in the nonextractable fraction of sedimentary organics have not been adequately studied and further work is required to clarify any possible correspondence with a temperature signal.

Hydrology and circulation in the Southern Cretan Sea during the CINCS experiment (May 1994–September 1995)

Article

Full-text available

Aug 2000
PROG OCEANOGR

Cited By (since 1996): 36, Export Date: 15 January 2013, Source: Scopus, CODEN: POCNA, doi: 10.1016/S0079-6611(00)00014-8, Language of Original Document: English, Correspondence Address: Georgopoulos, D.; National Centre for Marine Research, Aghios Kosmas, 166 04 Hellenikon, Greece, References: Balopoulos, E.Th., PELAGOS second annual progress report - A summary (1995), pp. 3-9. , PELAGOS, hydrodynamics and biogeochemical fluxes in the straits of the Cretan arc. Second annual progress report, 9/1994-8/1995, MAST project MAS2-CT93-0059. Athens: NCMRBruce, J.G., Charnock, H., Studies of winter sinking of cold water in the Aegean Sea (1965), 18, pp. 773-778. , Rapport du 18 e Congres de la Commision Internationale pour l'Exploration Scientifique de la Mer MediterraneeBurman, I., Oren, O.H., Water outflow close to bottom from the Aegean (1970) Cahiers Oceanographiques, 22, pp. 775-780;

Fatty acid dynamics in phytoplankton and microzooplankton communities during a spring bloom in the coastal Ligurian Sea: Ecological implications

Article

Full-text available

Jan 1989

During the spring of 1986, the 53 to 100 mu m size fraction of plankton was sampled at the entrance of the Villefranche-sur-Mer Bay. Populations were systematically identified and were then analysed for fatty acid composition using high resolution capillary gas chromatography. Marked variations in fatty acid composition were recorded, especially during periods when either the tintinnid Stenosemella ventricosa or the diatom Nitzschia seriata were dominant. Tintinnids were characterized by high values of (IsoC15:0 + AnteisoC15:0)/C15:0 and C18:1(n-7)/C18:1(n-9) ratios, and additionally by a previously unreported saturated branched fatty acid with 20 carbon atoms, which is tentatively identified as the 3, 7, 11, 15 tetramethylhexadecanoic acid. Alternatively, diatoms were characterized by high values of the Sigma C16/ Sigma C18 and C16:1/C16:0 ratios. Differences in the nutritional values of tintinnids versus diatoms for higher trophic levels evaluated from their fatty acid compositions are discussed.

Vertical flux of fatty acids in the North Atlantic Ocean

Article

Full-text available

Feb 1983

The quantitative and qualitative composition of fatty acids in particulate material collected in traps deployed during 98 days at 389, 988, 3755 and 5068 m depths in the equatorial North Atlantic was determined. The fatty acid composition indicates a predominantly marine source (14:0, 16:0, 16:1, 18:0, 18:1, 20:5, 20:4, 22:6, 22:5) with possibly a minor terrigenous component in the bathypelagic traps. The vertical fluxes of fatty acids and lipids decrease rapidly with depth. The rate of net loss of carboxylic acids increases with number of double bonds and decreases with number of carbon atoms. Iso- and anteiso- as well as some monoenoic fatty acids are more persistent, probably due to enhanced microbial synthesis during settling which counteracts degradation.

Implications of ??-Oxocarboxylic acids in the remote marine atmosphere for photo-Oxidation of unsaturated fatty acids

Article

Full-text available

Jan 1987

Specific organic compounds have been used as tracers of biological and anthropogenic source inputs to the marine atmosphere1–8. This tracer approach uses the unique molecular signatures or fingerprints for various lipid compound classes of marine and terrestrial plants to identify the sources of the organic substances in aerosols9. However, many of these substances are not stable and undergo transformation reactions. For example, unsaturated fatty acids, which are major constituents of marine and terrestrial plants, have not been frequently detected in remote marine aerosols3,6,7. The mechanism for the transformation of unsaturated fatty acids in the atmosphere has not been elucidated. In this paper, we report the discovery of a homologous series of ω-oxocarboxylic acids (C4–C14; C9 being maximum) in marine aerosols. We propose that these compounds are oxidation products of unsaturated fatty acids in the marine environment. The discovery of ω-oxoacids, along with additional aerosol, sea water, and rain data for mono- and di-carboxylic acids, has led us to postulate a photo-induced oxidative reaction scheme for unsaturated fatty acids in the marine atmosphere and surface seawater.

Enzymatic ω-Oxidation of Fatty Acids

Article

Full-text available

May 1964

Sterol and fatty acid composition of four marine Haptophycean algae

Article

Full-text available

May 1981
J MAR BIOL ASSOC UK

The lipids of four marine coccolithophorids (class Haptophyceae), Emiliania huxleyi, Hymenomonas carterae, Isochrysis galbana and Crystallolithus hyalinus, were examined by capillary gas chromatography-mass spectrometry. Fatty acids ranged from C14 to C22 and were predominantly of even chain length. The major acids were polyunsaturated C18 acids, 22:6 and either 14:0 or 16:0. C20 fatty acids were of low abundance. Significant amounts of octadecapentaenoic acid (18:5), previously thought to be unique to dinoflagellates, were identified in three of the algae. A small amount of a di-unsaturated C36 w-alkenoic acid was identified in E. huxleyi, which is the first report of such a long-chain fatty acid in any alga. Traces of wax esters, which are reportedly uncommon inalgae, were found in three of the species. The sterol distributions were very simple, with two or three compounds accounting for > 99% of the total sterols. In each case, the major component was 24-methylcholesta-5,22E-dien-3β-ol. H. carterae and C. hyalinus also contained 24-ethylcholesta-5,22E-dien-3β-ol and significant amounts of cholest-5-en-3β-ol were found in E. huxleyi and I. galbana. An unusual sterol, 23,24-dimethylcholesta-5,22E-dien-3β-ol, was identified in H. carterae. These sterols were mostly non-esterified although small amounts of sterol esters were identified in E. huxleyi. The lipid composition of E. huxleyi is distinctive in that it contains, in addition to the C36 fatty acid, novel C37–C39 unsaturated ketones and C31–C38 alkenes. Of the other coccolithophorids only I. galbana contained small quantities of one of the C3l alkenes.

Ozone-cyclohexene reaction in air: Quantitative analysis of particulate products and the reaction mechanism

Article

Full-text available

Apr 2002
ENVIRON SCI TECHNOL

Both gaseous and particulate products of the cyclohexene-ozone reaction were analyzed. Major gaseous products were aldehydes that consist of adipaldehyde (CHO(CH2)4CHO), glutaraldehyde (CHO(CH2)3CHO), and pentanal (CH,(CH,),CHO). The sum of the primary yields of aldehydes reaches as high as 50%. In addition to aldehydes, formic acid, CO, and C02 were produced, but formaldehyde was not detected. Main particulate products were adipaldehyde, 6-oxohexanoic acid (CHO(CH2)4COOH), adipic acid (HOOC(CH2)4COOH), glutaraldehyde, 5-oxopentanoic acid (CHO(CH2)3OOH), and glutaric acid (HOOC(CH2)3COOH). All these compounds were analyzed quantitatively, and the fraction of initial cyclohexene converted to aerosol organic carbon was estimated to be 13 +- 3% as the value extrapolated to a ppm concentration range of reactants. Although the reaction mechanism is in general explainable in terms of the Criegee mechanism, the reaction pathway to form formic acid is quite unique in this reaction system. The entire mechanism was discussed on the basis of the quantitative product analysis data.

Enzymatic ω-Oxidation of Fatty Acids

Article

May 1964

Nutrient sources and primary production in the Eastern Mediterranean

Article

Jan 1988
Oceanol Acta

Lipid components of the seagrasses Posidonia australis and Heterozostera tasmanica as indicators of carbon source

Article

Jan 1982

Peter D Nichols

Calibration of the alkenone paleotemperature index Uk'37 based on core-tops from the eastern South Atlantic and the global ocean (60°N-60°S)

Article

Jan 1998

Organic geochemical studies of Solar Lake laminated cyanobacterial mats

Article

Jan 1983

Aspects of the steroid geochemistry of a recent diatomaceous sediment from the Namibian Shelf

Article

Jan 1982
Oceanol Acta

Zooplankton and Nekton: Natural Barriers to the Seaward Transport of Suspended Terrigenous Particles off Peru

Article

Jan 1983

Some of the strongest biogenic signals of coastal upwelling reported in Recent marine sediments (e.g., organic carbon content >20 wt. %) are found in a mud facies on the inner continental margin off Peru, particularly between 10° and 14°S. Terrigenous sediments found there are anomalously fine grained and have overall grain-size distributions which are similar to those of deep-sea sediments collected seaward of the Peru Trench. To explain the observed dispersal patterns of fine silts and clays on the inner continental margin, rapid vertical transport of large aggregates (fecal pellets) from a wind-driven surface layer is required.

Geochemistry of Organic Matter in Ocean

Book

Jan 1984

E. A. Romankevich

Sorptive preservation of labile organic matter in marine sediments

Article

Aug 1994

ORGANIC matter preserved in marine sediments provides a molecular record of marine biological processes(1), accounts for approximately 20% of all carbon burial(2) and plays a key role in balancing the long-term flux of oxygen to the atmosphere(3). Only recently has it been appreciated that more than 90% of the organic matter preserved in most marine sediments is intimately associated with mineral surfaces(4). Little is known, however, of the effect that sorption to mineral surfaces might have in controlling either the lability or-quantity of-organic matter in the marine sedimentary record. The preserved organic material could be either intrinsically stable, or stabilized through interactions with mineral matrices. We show here that sorption of organic matter to mineral surfaces in marine sediments stabilizes the component molecules, slowing remineralization rates by up to five orders of magnitude. Sorptive protection can therefore account for the enigmatic preservation of intrinsically labile molecules such as amino acids and simple sugars in marine deposits(5,6) and links the preservation of organic carbon in marine sediments to the deposition of mineral surfaces.

Calibration of the alkenone paleotemperature index U37K' based on core-tops from the eastern South Atlantic and the global ocean (60oN-60oS) - Present and Past Circulation

Article

May 1998
GEOCHIM COSMOCHIM AC

We have analysed alkenones in 149 surface sediments from the eastern South Atlantic in order to establish a sediment-based calibration of the U37K′ paleotemperature index. Our study covers the major tropical to subpolar production systems and sea-surface temperatures (SST’s) between 0° and 27°C. In order to define the most suitable calibration for this region, the U37K′ values were correlated to seasonal, annual, and production-weighted annual mean atlas temperatures and compared to previously published culture and core-top calibrations. The best linear correlation between U37K′ and SST was obtained using annual mean SST from 0 to 10 m water depth (U37K′ = 0.033 T + 0.069, r2 = 0.981). Data scattering increased significantly using temperatures of waters deeper than 20 m, suggesting that U37K′ reflects mixed-layer SST and that alkenone production at thermocline depths was not high enough to significantly bias the mixed-layer signal. Regressions based on both production-weighted and on actual annual mean atlas SST were virtually identical, indicating that regional variations in the seasonality of primary production have no discernible effect on the U37K′ vs. SST relationship. Comparison with published core-top calibrations from other oceanic regions revealed a high degree of accordance. We, therefore, established a global core-top calibration using U37K′ data from 370 sites between 60°S and 60°N in the Atlantic, Indian, and Pacific Oceans and annual mean atlas SST (0–29°C) from 0 m water depth. The resulting relationship (U37K′ = 0.033 T + 0.044, r2 = 958) is identical within error limits to the widely used E. huxleyi calibrations of Prahl and Wakeham (1987) and Prahl et al. (1988) attesting their general applicability. The observation that core-top calibrations extending over various biogeographical coccolithophorid zones are strongly linear and in better accordance than culture calibrations suggests that U37K′ is less species-dependent than is indicated by culture experiments. The results also suggest that variations in growth rate of algae and nutrient availability do not significantly affect the sedimentary record of U37K′ in open ocean environments.

Eustigmatophyte microalgae are potential sources of C29 sterols, C22–C28n-alcohols and C28–C32n-alkyl diols in freshwater environments

Article

May 1999
ORG GEOCHEM

The neutral lipids of three freshwater microalgae from the class Eustigmatophyceae were examined to investigate possible algal sources of lipids in lacustrine sediments. The major neutral lipids in Eustigmatos vischeri (Hulbert) Taylor, Vischeria helvetica (Vischer et Pascher) Taylor and Vischeria punctata Vischer were sterols, long-chain alcohols and alkyl diols. The distributions of long-chain n-alkanols and n-alkenols were very similar in each species, but there were small interspecies differences in the proportions of alkyl diols. Saturated alcohols ranged from 14:0 to 28:0 (both present in trace amounts), with 22:0 as the major alkanol. The latter has previously been reported to be the major n-alcohol in some lacustrine sediments. C16–C30 monounsaturated alcohols were more abundant: 26:1 and 28:1 were the major constituents. The sterol distributions consisted predominantly of 24-ethylcholesterol with small amounts of cholesterol, 24-methylcholesterol, 24-ethylcholesta-5,22E-dien-3β-ol and isofucosterol. These results add to the growing list of microalgae that contain a high proportion of 24-ethylcholesterol, which is more typically associated with higher plants. The long-chain alkyl diols ranged from C28 to C32: the major constituents were the C28 1,13-diol and C30 and C32 1,15 diols which occurred together with smaller amounts of other positional isomers. C30 and C32 alkyl diols have been found in marine eustigmatophytes of the genus Nannochloropsis, and these new results confirm that the same class of compounds occurs in freshwater eustigmatophytes.

Essential polyunsaturated fatty acids from 14 species of diatom (Bacillariophyceae)

Article

Dec 1993

The lipid class and total fatty acid compositions of 14 species of diatom (class Bacillariophyceae) were examined. The major lipid class in these microalgae was polar lipid (50.1-90.8%), although in some species, triacylglycerols (0.3-47.7%) and free fatty acids (0-29.2%) were also abundant in the logarithmic phase cultures. The major fatty acids in most species were 14:0, 16:0, 16:1 (n-7) and 20:5(n-3). The polyunsaturated fatty acids 16:2(n-4), 16:3(n-4), 16:4(n-1), 18:4(n-3) and 22:6(n-3) also comprised a significant proportion (>4% each) of the total fatty acids in some species. The characteristic fatty acid composition of diatoms is readily distinguishable from those of other classes of microalgae. The mean proportion of 22:6(n-3) was significantly higher in representatives from the order Centrales (4.9%) than the Pennales (1.6%), but there was no consistent difference in the proportions of the other fatty acids. Four of the pennate diatoms contained significant proportions of arachidonic acid, 20:4(n-6) (3.5-5.6%), but most species examined contained very low proportions of (n-6) polyunsaturated fatty acids. Based on the lipid compositions, all of the diatom species studied are potentially suitable sources of some of the longer chain polyunsaturated fatty acids.

Vertical flux of hydrocarbons as measured in sediment traps in the eastern North Pacific Ocean

Article

Nov 1986
MAR CHEM

Sediment trap experiments were conducted at three stations (Stn. 5 at 4750 m depth, 7 at 4330 m depth and 11 at 3880 m depth) in the California Current and its adjacent areas in the eastern North Pacific from December 1982 to January 1983 to collect sinking particles, which were analyzed for organic carbon and hydrocarbons.The vertical fluxes of organic carbon, total nitrogen and lipid carbon at any depth decreased in the following order: Stn. 5 > Stn. 11 > Stn. 7, the same trend as the standing stocks of chl. a at these station, which suggests that regional variation of organic matter flux is considerably influenced by the primary productivity in the surface water layer.Hydrocarbons of the sinking particles consisted of n-C15–C20 with a maximum of n-C17, n-C21–C32, n-C21:6 and three branched C25 alkenes (br-C25:3, br-C25:3, and br-C25:4), but any odd or even carbon number predominance in n-C21–C32 was not observed. n-C21:6 and n-C17 were the most abundant throughout the depths at Stn. 5, while only n-C17 was a major component of the sinking particles from the intermediate layers, but not from the deep layers, at Stns. 7 and 11. Thus, there were clear regional and vertical variabilities of hydrocarbon composition in the sinking particles.The vertical flux of various hydrocarbons at the three stations tended to decrease exponentially with depth. The attenuation constants of the hydrocarbon fluxes were calculated by analysis of the relationship between the fluxes and depths. Half-depth of the flux calculated from the attenuation constant showed extensive variability for the hydrocarbon species and the location of the station. The values of the half-depths of n-C17, Σn-C15–20, n-C21:6 and pristane were lower than those of Σn-C21–32 and Σbr-C25, indicating that hydrocarbons derived from phytoplankton are more susceptible to biological degradation than those from zooplankton.The half-depths of the hydrocarbon fluxes tended to increase as follows: Stn. 7 < Stn. 11 < Stn. 5. This trend was the same as the size of the sinking particles collected at these stations, which suggests that the sinking rate of the particles tends to increase in the order of Stns. 7, 11 and 5. Thus, these data indicate that the sinking rate of the particles is a primary factor in determining the hydrocarbon compositon of the particles in the intermediate and deep waters.

The transport and budget of sterols in the western North Atlantic Ocean

Article

Sep 1979

A general correlation exists between total free sterols, particulate organic carbon, particulate organic nitrogen, and chlorophyll a in the upper 300 m of the water column in the western North Atlantic Ocean. High values are found in shelf waters and in the subsurface chlorophyll a maximum in the Sargasso Sea, lower values at a Gulf Stream meander or ring fringe station. A diatom sterol, 24‐methylcholesta‐5,22‐dienol, appears to be produced only within the euphotic zone. Below this, consumption or removal processes dominate and the concentration of this compound decreases with depth. On the other hand, a zooplankton sterol, cholesterol, occurs throughout the water column, exhibiting maxima at the base of the mixed layer and at depths where particles tend to accumulate because of favorable chemical or density gradients. Flux calculations show that at most 0.05–0.3% of the sterols produced by phytoplankton in Sargasso Sea surface waters is deposited to the ocean floor. The sterol residence time (the average lifetime of a sterol molecule before it is metabolized) in the euphotic zone was calculated to be about 1 month, whereas the deep water residence time is 20–150 years.

Dicarboxylic acid salts and?,?-dicarboxylic acids: Photooxidation products of unsaturated fatty acids, present in marine aerosols and marine sediments

Article

Mar 1992
NATURWISSENSCHAFTEN

Euripides G Stephanou

The large deep water transient in the Eastern Mediterranean

Article

Mar 1999
DEEP-SEA RES PT I

The recent changes in the thermohaline circulation of the Eastern Mediteranean caused by a transition from a system with a single source of deep water in the Adriatic to one with an additional source in the Aegean are described and assessed in detail. The name Cretan Sea Overflow Water (CSOW) is proposed for the new deep water mass. CSOW is warmer (θ>13.6°C) and more saline (S>38.80) than the previously dominating Eastern Mediterranean Deep Water (EMDW), causing temperatures and salinities to rise towards the bottom. All major water masses of the Eastern Mediterranean, including the Levantine Intermediate Water (LIW), have been strongly affected by the change. The stronger inflow into the bottom layer caused by the discharge of CSOW into the Ionian and Levantine Basins induced compensatory flows further up in the water column, affecting the circulation at intermediate depth. In the northeastern Ionian Sea the saline intermediate layer consisting of Levantine Intermediate Water and Cretan Intermediate Water (CIW) is found to be less pronounced. The layer thickness has been reduced by factor of about two, concurrently with a reduction of the maximum salinity, reducing advection of saline waters into the Adriatic. As a consequence, a salinity decrease is observed in the Adriatic Deep Water. Outside the Aegean the upwelling of mid-depth waters reaches depths shallow enough so that these waters are advected into the Aegean and form a mid-depth salinity-minimum layer. Notable changes have been found in the nutrient distributions. On the basin-scale the nutrient levels in the upper water column have been elevated by the uplifting of nutrient-rich deeper waters. Nutrient-rich water is now found closer to the euphotic zone than previously, which might induce enhanced biological activity. The observed salinity redistribution, i.e. decreasing values in the upper 500–1400m and increasing values in the bottom layer, suggests that at least part of the transition is due to an internal redistribution of salt. An initiation of the event by a local enhancement of salinity in the Aegean through a strong change in the fresh water flux is conceivable and is supported by observations.

Microbial lipids of an intertidal sediment—I. Fatty acids and hydrocarbons

Article

Aug 1980
GEOCHIM COSMOCHIM AC

A detailed study has been made of the solvent extractable monocarboxylic, dicarboxylic and hydroxylated fatty acids and n-alkanes in a surface intertidal sediment, and the distributions compared to microorganisms cultured from the sediment. Diatoms are shown to contribute most of the monocarboxylic acids, particularly the significant amounts of polyunsaturated acids present, and a small proportion of the n-alkanes. Bacteria contribute between 11 and 14% of the monocarboxylic acids and markers for this, including trans-monounsaturated acids, are proposed. Detritus from the sea-grass Zostera muelleri is a major source of the α-hydroxy-, ω-hydroxy and α,ω-dicarboxylic acids in the sediment and a minor contributor of n-alkanes and long-chain fatty acids.

Organic aerosols in Eastern Mediterranean: Components source reconciliation by using molecular markers and atmospheric back trajectories

Article

Dec 1996
ORG GEOCHEM

Molecular markers, such as n-alkanes, hopanes, PAHs, n-alkanols, n-alkanals, n-alkan-2-ones and n-alkanoic acids, and atmospheric back trajectories have been conjointly used to reconcile Eastern Mediterranean marine organic aerosols with their emission sources. In the urban site, local inputs of polar and non polar lipids control the aerosol composition. In addition the presence of iso- and anteisoalkanes in the aliphatic fraction of all urban samples analysed, demonstrated the contribution of cigarette smoke to urban aerosols. The composition of the aliphatic and aromatic fractions demonstrated a clear petrogenic input. In the rural site the composition and concentrations of the PAH fraction were dependant on the origin of air masses, and showed a rather pyrolytic origin. They were higher for air masses from the north than for air masses originating from the south. Some molecular markers, such as 6,10,14-trimethylpentadecan-2-one and α,ω-dicarboxylic acids with Cn > C20, characterized rural aerosols corresponding to air masses with a pronounced marine origin.

Free and bound fatty acids and hydroxy fatty acids in the living and decomposing eelgrass Zostera marina L

Article

Aug 1995
ORG GEOCHEM

Very early diagenetic processes of free, esterified and amide or glycosidically bound fatty acids and hydroxy fatty acids present in well documented samples of living and decomposing eelgrass (Zostera marina L.) were investigated. Free and esterified fatty acids decreased significantly over a period of decay of 12.5 years, although their distribution patterns were largely unchanged. Amide or glycosidically bound α-hydroxy fatty acids and the newly recognized α,β-dihydroxy fatty acids were not degraded. Thus both, but in particular the α,β-dihydroxy fatty acids, may serve as potential biomarkers for the recognition of eelgrasses in palaeoenvironments. The increasing amounts of ω-hydroxy fatty acids and α,ω-dicarboxylic fatty acids upon decay indicate bacterial transformations of eelgrass lipids. This bacterial action was further demonstrated by a substantial increase of amide-bound β-hydroxy fatty acids derived from LPS of gram-negative bacteria.

Benthic–pelagic coupling in the oligotrophic Cretan Sea

Article

Aug 2000
PROG OCEANOGR

During the EU-MAST2 project CINCS (pelagic-benthic Coupling IN the oligotrophic Cretan Sea), sediment community oxygen consumption (SCOC) was measured during the winter and summer of 1995. Satellite CZCS images showed a different phytoplankton biomass in the surface water during these two periods. SCOC was measured in-situ with a benthic lander at depths ranging from 40 to about 1600 m. In conjunction to the SCOC measurements, microbial biomass and chlorophyll content of the surface layer of the sediment were also determined. SCOC, microbial biomass and the chlorophyll concentration displayed similar spatial and temporal trends, i.e. a steady decrease with increasing water depth in both seasons, with lower values occuring below 40 m depth during the summer. In winter SCOC ranged from 438 μmol m−2 h−1 at 40 m depth to 37 μmol m−2 h−1 at 1570 m which is equivalent to carbon mineralisation varying from 107 to 9 mg C m−2 d−1, respectively. SCOC values in the summer were about half the winter values except at the 40 m station where the opposite was found. Short-term deployments of a sediment trap 4 m above the sea floor showed diminished vertical fluxes of phytodetritus were lower in summer at all stations including 40 m depth. It is argued, partially on the basis of oxygen microprofiles, that the enhanced sedimentary concentration and decreased vertical flux of chlorophyll in summer at 40 m are primarily caused by benthic primary production. The results from the other stations show that in an highly oligotrophic sea such as the Cretan Sea, pelagic-benthic coupling exists although the amplitude of the seasonal signal is small. Moreover, the bathymetric trends in benthic microbial biomass and SCOC indicate that there is no substantial horizontal transport of labile organic material down the slope.

Bacterial response to seasonal changes in labile organic matter composition on the continental shelf and bathyal sediments of the Cretan Sea

Article

Aug 2000
PROG OCEANOGR

Bacterial abundance, biomass and cell size were studied in the oligotrophic sediments of the Cretan Sea (Eastern Mediterranean), in order to investigate their response to the seasonal varying organic matter (OM) inputs. Sediment samples were collected on a seasonal basis along a transect of seven stations (ranging from 40 to 1570 m depth) using a multiple-corer. Bacterial parameters were related to changes in chloroplastic pigment equivalents (CPE), the biochemical composition (proteins, lipids, carbohydrates) of the sedimentary organic matter and the OM flux measured at a fixed station over the deep basin (1570 m depth). The sediments of the Cretan Sea represent a nutrient depleted ecosystem characterised by a poor quality organic matter. All sedimentary organic compounds were found to vary seasonally, and changes were more evident on the continental shelf than in deeper sediments. Bacterial abundance and biomass in the sediments of the Cretan Sea (ranging from 1.02 to 4.59 × 108 cells g−1 equivalent to 8.7 and 38.7 μgC g−1) were quite high and their distribution appeared to be closely related to the input of fresh organic material. Bacterial abundance and biomass were sensitive to changes in nutrient availability, which also controls the average cell size and the frequency of dividing cells. Bacterial abundance increased up to 3-fold between August '94 and February '95 in response to the increased amount of sedimentary proteins and CPE, indicating that benthic bacteria were constrained more by changes in quality rather than the quantity of the sedimentary organic material. Bacterial responses to the food inputs were clearly detectable down to 10 cm depth. The distribution of labile organic compounds in the sediments appeared to influence the vertical patterns of bacterial abundance and biomass. Cell size decreased significantly with water depth. Bacterial abundance and biomass were characterised by clear seasonal changes in response to seasonal OM pulses. The strong coupling between protein flux and bacterial biomass together with the strong bacterial dominance over the total biomass suggest that the major part of the carbon flow was channelled through the bacteria and the benthic microbial loop.

A study of food chains in seagrass communities: I. Lipid components of the seagrasses Posidonia australis and Heterozostera tasmanica as indicators of carbon source

Article

Dec 1982
PHYTOCHEMISTRY

The component hydrocarbons, sterols, alcohols, monocarboxylic, α, ω-dicarboxylic and ω-hydroxy acids of the seagrasses Posidonia australis and Heterozostera tasmanica and a sample of P. australis detritus are reported. The fresh leaves of P. australis and P. australis detritus are characterized by a distinctive distribution of solvent-extractable long-chain monocarboxylic, α, ω-dicarboxylic and ω-hydroxy acids. This distinctive pattern should enable these lipid components along with other distinctive components to be used as chemical markers of the seagrass P. australis. H. tasmanica is characterized by (1) higher relative concentrations of 16:2ω6 and 16:3ω3 than P. australis, (2) the absence of the distinctive distribution pattern of long-chain monocarboxylic and ω-hydroxy acids observed for P. australis, (3) the absence of α, ω-diacids and (4) a lower absolute concentration of ω-hydroxy acids than P. australis.

Chemistry of waxes of higher plants

Article

A. P. Tulloch

C18Isoprenoid Ketone in Recent Marine Sediment

Article

Jul 1973
NATURE

ISOPRENOID hydrocarbons, fatty acids and alcohols occur in ancient rocks, oil shales, young sediments and living organisms1,2. During thermal alteration experiments on a recent marine sediment from Tanner Basin, Southern California continental shelf, we isolated a C18-isoprenoid ketone, namely 6,10,14-trimethylpentadecan-2-one. Samples of sediment from the Tanner Basin were sealed in glass bombs and exposed to temperatures from 60° to 150° C for 7 d, 30 d and 60 d. The sediment was then extracted with benzene-methanol and the extract chromatographed on a silicic acid column. The ketone was found in both the heat-treated and untreated sediment. It was extracted with the fatty acid fraction which had been converted to methyl esters, and was separated with the other branched components by the urea adduction method. For comparative purposes, the C18-isoprenoid ketone was also synthesized3. Analytical comparisons by gas-liquid chromatography, using two 5 foot × ⅛ inch columns (3% OV 101 on 100/120 mesh `Gas Chrom' Q and 3% DEGS on 100/120 mesh `Gas Chrom' Z), showed the synthetic product to be identical to the sedimental ketone.

Steroid transformations in Recent marine sediments

Article

Dec 1980
Phys Chem Earth

The surface sediments and overlying water column from 3 Recent sedimentary environments-Walvis Bay off southwestern Africa, the Black Sea and the western North Atlantic-have been analyzed for stenols and their transformation products, stanols, sterenes, and steroid ketones. The steroid distributions in surface sediments are controlled by inputs from source organisms and from microbial or chemically mediated reactions occurring at the sediment-water interface or in the overlying water column. A general correlation was found to exist for various steroidal compounds in sediments from each area, suggesting related reaction sequences. Also, the steroid transformation products correlated with photoproduction in the overlying waters as well as with the oxic and anoxic conditions of the sedimentary environment.

Identification of a “pool” of lipid photoproducts in senescent phytoplanktonic cells

Article

Nov 1998
ORG GEOCHEM

The photodegradation of different lipid compounds was studied in killed cells of Phaeodactylum tricornutum and Dunaliella sp. Chlorophyll phytyl chain was photodegraded to 6,10,14-trimethylpentadecan-2-one and 3-methylidene-7,11,15-trimethylhexadecan-1,2-diol, sterols to 5α- and 6α/6β-hydroxysterols, carotenoids to loliolide and iso-loliolide, and unsaturated fatty acids to C7–C11ω-oxocarboxylic and α,ω-dicarboxylic acids. After elimination of the insufficiently specific photoproducts, 3-methylidene-7,11,15-trimethylhexadecan-1,2-diol, 5α- and 6α/6β-hydroxysterols, C7–C11ω-oxocarboxylic and α,ω-dicarboxylic acids (with C9 as the most abundant species) were selected to constitute a “pool” of useful indicators of photooxidative alterations of phytoplankton.

Annual Biomarker Record for Export Production in the Central Arabian Sea

Article

Dec 2000
DEEP-SEA RES PT II

The record for plankton biomarkers in sediment trap samples from a one-year experiment in the central Arabian Sea (AS4: 15°59′N 61°30′E) shows variations that reflect changing biological conditions in surface waters. Particulate fluxes of C37–39 alkenones, highly branched C25 isoprenoids (HBI), dinosterol, nC28 12-hydroxy fatty acid, 24-ethylcholesterol, and a C30–34 series of pentacyclic triterpanols all displayed distinct maxima at the start and stop of the Northeast (NE) and Southwest (SW) Monsoons. Surface mixing conditions changed rapidly at these times, altering light and nutrient availability, thereby triggering these biomarker signals of export production. Temporal offsets noted in individual biomarker concentrations (per g total organic carbon) at the start of the SW Monsoon suggest succession occurs in the phytoplankton community contributing to organic matter export. Comparable offsets were neither apparent at the start of the less dynamic NE Monsoon nor at the end of the NE or SW Monsoons. Broad concentration maxima for HBI also were observed at the beginning and end of the time-series during the relatively quiescent Fall Intermonsoon period when such features were conspicuously absent for other biomarkers. HBI are reputed biomarkers of Rhizoselenia and Haslea spp., two recognized dominants of diatom biomass in the Arabian Sea. These peaks in biomarker concentration could reflect either changes in the relative proportion of specific organisms that contribute to the upper ocean productivity or enhanced preservation of the biomarkers during times of high export production. In either case, the biomarker record in sediment traps reflects important changes in the biological condition of the upper ocean.

A Review of Sterol Markers for Marine and Terrigenous Organic Matter

Article

Dec 1986
ORG GEOCHEM

John K Volkman

A review of literature on the occurrence of 4-desmethyl sterols in unicellular algae indicates that few sterols are sufficiently restricted in distribution to be considered unambiguous markers for specific algal groups. Almost all of the 4-desmethyl sterols found in higher plants occur in marine algae, sometimes as major constituents, so sterol distributions do not always allow to distinguish between marine or terrigenous organic matter. Some of the problems associated with the use of sterols as markers for specific sources are highlighted by comparison of the sterol distribution in selected marine sediments and seawater samples. Although each sediment represents a very different depositional environment the sterol distributions are surprisingly similar. The sterol distributions in a saline Antarctic lake and samples of particulate matter from oligotrophic waters off the east Australian coast show that marine phytoplankton biosynthesize a wide range of sterols, including large amounts of 24-ethylcholest-5-en-3β-ol which is often used as a marker for terrigenous organic matter. Similar distributions occur in marine sediments from the upwelling area off Peru and in temperate intertidal sediments despite large differences in algal productivity between the two areas. In deeper sediments, most of the sterols are not derived from phytoplankton but from higher plants. These data indicate that inferences drawn from sterol distributions regarding sources of organic matter must be made with caution and should be supported using other lipid data. It further follows that in ancient sediments and crude oils a high proportion of C29 steranes need not indicate that most of the organic matter was derived from vascular plants.

Association reactions of Na(+) and some implications for interstellar chemistry

Article

Aug 1983

Three-body association reactions of Na+ with a variety of neutral gases in the presence of He as third body have been studied in a Selected Ion Flow Tube at 80K. The measured rate coefficients have been utilized to estimate radiative association rate coefficients at 20K. It is shown that Na+-neutral radiative association reactions play a role in the depletion of Na+ in dense interstellar clouds and can produce a sufficient amount of NaOH to explain its observed tentative abundance in Sgr B2.

Potential palaeoenvironmental information of C24 to C36 mid-chain diols, keto-ols and mid-chain hydroxy fatty acids; A critical review

Article

Aug 1997
ORG GEOCHEM

The environmental occurrence of long-chain mid-chain diols, keto-ols and mid-chain hydroxyl fatty acids is reviewed. The published information is heavily biased towards organic-rich sediments, which strongly hampers interpretation. The composition of positional isomers of these compounds differs remarkably between cultures of microalgae from the genus Nannochloropsis , and sediments, suggesting that these algae are not the major sources for the compounds to the sediments. The composition of diols and keto-ols differs substantially between marine and freshwater environments, and between marine environments themselves. These observations may be useful in palaeo-environmental reconstructions, particularly in identifying freshwater influx. Lack of overlap in the composition of positional isomers suggests that keto-ols do not originate from diols diagenetically, but are derived from as yet unknown organisms.

Sedimentological processes in the southern margin of the Cretan Sea (NE Mediterranean)

Article

Aug 2000
PROG OCEANOGR

The Cretan Basin can be characterized as a back-arc basin of the Hellenic Trench System, that is related to the subduction zone of the African Plate under the Eurasia Plate. The study area includes the narrow and relatively steep (gradient 1.5°) continental shelf of the island of Crete followed by the steep slope (2°–4°) and the rather flat deeper part of the Cretan basin (water depths 1700 m). Surficial sediments of the coastal zone are coarser and of terrigenous origin, while in deeper waters finer sediments, of biogenic origin, are more abundant. Sand-sized calcareous sediment accumulations, identified in middle-lower slope, may be attributed to the aggregation of seabed biogenic material related to the near bed current activity. High resolution profiles (3.5 kHz) taken from the inner shelf shows a typical sigmoid-oblique progradational configuration, implying prodelta sediment accumulation during the Hol-ocene. In the upper-middle slope, sub-bottom reflectors indicate continuous sedimentation of alternating fine and/or coarse grained material. Small-scale gravity induced synsedimentary faults appeared, locally. In contrast, a series of gravity induced faults, identified in the lower slope, are associated with sediment instabilities due to seismotectonic activity. Sediment cores taken from the shelf-break consists of calcareous muddy sand with small amounts of terrigen-ous silt and fine sand, while the cores recovered from the middle slope has revealed a more homogeneous fine sediment texture of hemipelagic deposition. The prevailing accumulation processes in the southern margin of the Cretan basin are: (i) prodelta deposition in the inner-middle shelf; (ii) settling from bottom nepheloid layers in the shelf and upper slope; (iii) calcareous sediment formation due to settling from suspension and post accumulation aggregation (middle-lower slope); (iv) long-term episodic sediment gravity processes in the lower slope; and (v) to a lesser extent, redeposition from resuspension due to gravity processes and bottom currents.

Corrigendum to “Marine organic geochemistry of the Eastern Mediterranean: 2. Polar biomarkers in Cretan Sea surficial sediments” [Marine Chemistry 85 (2004) 1–25]

Abstract

No full-text available

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