Degradation state of organic matter in surface sediments from the Southern Beaufort Sea: a lipid approach

For the next decades significant climatic changes should occur in the Arctic zone. The expected destabilisation of permafrost and its consequences for hydrology and plant cover should increase the input of terrigenous carbon to coastal seas. Consequently, the relative importance of the fluxes of terrestrial and marine organic carbon to the seafloor will likely change, strongly impacting the preservation of organic carbon in Arctic marine sediments. Here, we investigated the lipid content of surface sediments collected on the Mackenzie basin in the Beaufort Sea. Particular attention was given to biotic and abiotic degradation products of sterols and monounsaturated fatty acids. By using sitosterol and campesterol degradation products as tracers of the degradation of terrestrial higher plant inputs and brassicasterol degradation products as tracers of degradation of phytoplanktonic organisms, it could be observed that autoxidation, photooxidation and biodegradation processes act much more intensively on higher plant debris than on phytoplanktonic organisms. Examination of oxidation products of monounsaturated fatty acids showed that photo- and autoxidation processes act more intensively on bacteria than on phytodetritus. Enhanced damages induced by singlet oxygen (transferred from senescent phytoplanktonic cells) in bacteria were attributed to the lack of an adapted antioxidant system in these microorganisms. The strong oxidative stress observed in the sampled sediments resulted in the production of significant amounts of epoxy acids and unusually high proportions of monounsaturated fatty acids with a trans double bond. The formation of epoxy acids was attributed to peroxygenases (enzymes playing a protective role against the deleterious effects of fatty acid hydroperoxides in vivo), while cis/trans isomerisation was probably induced by thiyl radicals produced during the reaction of thiols with hydroperoxides. Our results confirm the important role played by abiotic oxidative processes in the degradation of marine bacteria and do not support the generally expected refractory character of terrigenous material deposited in deltaic systems.

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title: Sedimentary organic matter preservation: an assessment and speculative synthesis
abstract: Throughout Earth history, almost all preserved organic matter has been incorporated in marine sediments deposited under oxygenated waters along continental margins. Given modern oceanic productivity and sediment burial rates of 50 × 1015 and 0.16 × 1015 gC yr−1, respectively, organic preservation in the marine environment is < 0.5% efficient. Although correlative information is often used to suggest that productivity, sediment accumulation rate, bottom water oxicity, and organic matter source are key variables, the mechanisms governing sedimentary organic matter preservation have remained unclear. 
 
The factors which directly determine preservation vary with depositional regime, but have in common a critical interaction between organic and inorganic materials over locally variable time scales. More than 90% of total sedimentary organic matter from a wide variety of marine depositional environments cannot be physically separated from its mineral matrix. This strongly associated organic component varies directly in concentration with sediment surface area and thus appears to be sorbed to mineral grains. Sediments accumulating outside deltas along continental shelves and upper slopes characteristically exhibit mineral surface area loadings approximately equivalent to a single molecular covering. These monolayer-equivalent coatings include a fraction of reversibly bound organic molecules that are intrinsically labile, but resist appreciable mineralization as they pass rapidly through oxygenated surface sediments and are preserved within underlying anoxic deposits. The delivery of mineral surface area is the primary control on organic matter preservation within these expansive coastal margin regions where roughly 45% of all organic carbon accumulates. 
 
Deltaic sediments account for roughly another 45% of global carbon burial, but often exhibit much less than monolayer-equivalent organic coatings. This pattern is seen in periodically oxygenated sediments off the mouth of the Amazon River, even though the component clastic minerals are discharged by the river with monolayer coatings. Comparably extensive losses of organic matter, including distinct particles such as pollen grains, occur in the surfaces of deep-sea turbidites in which long term reaction with O2 is clearly the causative factor. Sub-monolayer organic coatings also are observed in continental rise and abyssal plain sediments where slower accumulation rates and deeper O2 penetration depths result in increased oxygen exposure times and little (~ 5% of the global total) organic matter preservation. A transition zone between monolayer and sub-monolayer organic coatings apparently occurs on lower continental slopes, and is marked along the Washington coast by parallel offshore decreases in total organic matter and pollen between 2000–3000 m water depth. 
 
Sediments underlying highly productive, low-oxygen coastal waters such as off Peru and western Mexico are characteristically rich in organic matter, but account for only ~ 5% of total organic carbon burial. These sediments show a direct relationship between organic matter content and mineral surface area, but at organic loadings 2–5 times a monolayer equivalent. Organic materials sorbed in excess of a monolayer thus also may be partially protected. Such high sedimentary organic contents may result from equilibration with DOM-rich porewaters, or very brief O2 exposure times which allow preservation of extremely oxygen-sensitive organic materials such as pigments and unsaturated lipids. Thus organic matter preservation throughout much of the ocean may be controlled largely by competition between sorption at different protective thresholds and oxic degradation. 
 
Future research strategies should be specifically directed at delineating the mechanisms for organic matter preservation in marine sediments. In particular, special effort is needed to determine the amounts and types of sorbed organic materials and the nature of their bonding to mineral surfaces. The extent and dynamics with which organic molecules are partitioned between porewaters and solid phases also should be determined, as well as the effects of these phase associations on their reactivities toward chemical and biological agents. In addition, processes for slow oxic (and suboxic) degradation of organic materials bear investigation in deep-sea sediments, as well as in other extreme environments such as oxidizing turbidites, weathering shales, and soils. Such studies should include characterizations of hydrolysis-resistant organic materials and emphasize the complementary use of biochemical compositions with readily separable particles such as pollen to calibrate and typify the mechanisms and stages of sedimentary organic degradation.

title: What happens to terrestrial organic matter in the ocean
abstract: Each year rivers transport approximately 0.25×10 15  g of dissolved ( μ m) organic carbon (DOC) and 0.15×10 15  g of particulate (>0.5  μ m) organic carbon (POC) from continents to the ocean. Global discharge of riverine DOC is sufficient alone to sustain turnover of the entire pool of organic carbon dissolved in seawater. Similarly, the input of terrestrial POC by rivers is adequate to supply all the organic carbon buried in marine sediments. Because riverine organic matter consists of highly degraded, nitrogen-poor remains of terrestrial organisms, it might be expected to suffer minimal respiration in the ocean. One of the biggest mysteries in the global carbon cycle, therefore, is that only a small fraction of the organic matter dissolved in seawater and preserved in marine sediments appears to be land-derived. Either our global budgets and distribution estimates are greatly in error, or both dissolved and particulate organic matter of terrestrial origin suffer rapid and remarkably extensive remineralization at sea. Although many uncertainties remain, recent studies provide growing evidence for destruction of both dissolved and particulate terrestrial organic matter in the ocean. The mechanisms by which these huge masses of organic materials might be so rapidly oxidized following discharge are largely unknown. This report focuses on the transport and transformations of land-derived organic matter in the ocean, highlighting recent research on the patterns and processes involved.

title: Lipid composition of the pelagic crab Pleuroncodes planipes, its feces, and sinking particulate organic matter in the Equatorial North Pacific Ocean☆
abstract: Fecal pellets from the pelagic crab Pleuroncodes planipes were a substantial portion of the particulate organic matter in a sediment trap deployed at the bottom of the mixed layer in the eastern tropical North Pacific Ocean. The lipids of fresh P. planipes feces were compared to lipids of the sediment trap material, of mixed zooplankton which may comprise part of the diet of the crab, and of the crab itself in order to elucidate the source of organic compounds found in the trap. Hydrocarbons, wax esters, triacylglycerols, steroidal alcohols, steroidal ketones, and fatty acids were determined by capillary gas chromatography and gas chromatography/mass spectrometry. Significant input of lipids via sedimentation of crab fecal material is indicated, and modification of dietary lipid within the gut of the crab is inferred. Labile dietary fatty acids are depleted and sterols enriched in the fecal pellets and trap material relative to the zooplankton and crab. Nuclear saturated and unsaturated 3-ketosteroids and unsaturated steroidal hydrocarbons were detected in the crab, its feces, and in the sediment trap particulate material.

title: Differential transport and degradation of bulk organic carbon and specific terrestrial biomarkers in the surface waters of a sub-arctic brackish bay mixing zone
abstract: Differential transport and degradation of bulk organic carbon and specific terrestrial biomarkers in the surface waters of a sub-arctic brackish bay mixing zone

title: Biogeochemistry of suspended and sedimentary material in the Ob and Yenisei rivers and Kara Sea: amino acids and amino sugars
abstract: Suspended particulate matter (SPM) and sediments were sampled in the Ob and the Yenisei rivers and the adjacent Kara Sea up to 77°N during the ice-free period in August and September 1997 (only sediments), 1999 and 2000. The material was analyzed for organic carbon (OC) and nitrogen (N) as well as for the content and monomeric composition of the labile organic constituents amino acids (AA) and amino sugars (AS). Despite interannual variation, surface SPM concentration generally revealed decreasing values from 8 to 4 mg/L for the Ob and Yenisei to values

title: How depositional conditions control input, composition, and degradation of organic matter in sediments from the Chilean coastal upwelling region
abstract: In a comprehensive study, we compared depositional conditions, organic matter (OM) composition, and organic carbon turnover in sediments from two different depositional systems along the Chilean continental margin: at ∼23° S off Antofagasta and at ∼36° S off Concepcion. Both sites lie within the Chilean coastal upwelling system and have an extended oxygen minimum zone in the water column. However, the northern site (23° S) borders the Atacama Desert, while the southern site (36° S) has a humid hinterland. Eight surface sediment cores (up to 30 cm long) from water depths of 126–1350 m were investigated for excess 210Pb (210Pbxs) activity, total organic and total inorganic carbon concentrations (TOC and TIC, respectively), C/N-ratios, organic carbon isotopic compositions (δ13C), chlorin concentrations, Chlorin Indices (CI), and sulfate reduction rates (SRR). Sediment accumulation rates obtained from 210Pb-analysis were similar in both regions (0.04–0.15 cm yr−1 at 23° S, 0.10–0.19 cm yr−1 at 36° S), although total 210Pbxs fluxes indicated that the vertical particle flux was higher at 36° S than at 23° S. We propose that sediment focusing in isolated deposition centers led to high sediment accumulation rates at 23° S. Furthermore, there were no indications for sediment mixing at 23° S, while bioturbation was intense at 36° S. δ13C-values (−24.5‰ to −20.1‰ vs. VPDB) and C/N-ratios (molar, 8.6–12.8) were characteristic of a predominantly marine origin of the sedimentary OM in both investigated areas. The extent of OM alteration in the water column was partly reflected in the surface sediments as chlorin concentrations decreased and C/N-ratios and CI increased with increasing water depth of the sampling site. SRR were lower at 23° S (areal SRR 0.12–0.60 mmol m−2 d−1) than at 36° S (areal SRR 0.82–1.18 mmol m−2 d−1), which was partly due to the greater water depth of most of the sediments investigated in the northern region and consistent with a lower quality of the sedimentary OM at 23° S. Reaction rate constants for TOC degradation that were obtained from measured SRR (kSRR; 0.0004–0.0022 yr−1) showed a good correspondence to kTOC that were derived from the depth profiles of TOC (0.0003–0.0014 yr−1). Both, kSRR and kTOC, reflect differences in OM composition. At 36° S they were related to the degradation state of bulk OM (represented by C/N-ratios), whereas near 23° S they were related to the freshness of a small fraction of labile OM (represented by CI). Our study shows that although rates of organic carbon accumulation were similar in both investigated sites, the extent and kinetics of organic carbon degradation were closely linked to differing depositional conditions.

title: Distribution and lability of land-derived organic matter in the surface sediments of the Rhône prodelta and the adjacent shelf (Mediterranean Sea, France): a multi proxy study
abstract: The Gulf of Lions is a river-dominated ocean margin that receives high loads of nutrients and particulate matter from the Rhone River but most particulate materials settle rapidly on the nearshore seafloor. One question is raised on the fate of these large quantities of organic carbon delivered by the river to the coastal marine environment. Surface sediments (0–0.5 cm) were collected in the Rhone prodelta and its adjacent shelf during a period of low river discharge (April 2007, 16 stations). The sources, distribution and lability of sedimentary organic matter were examined using bulk (organic carbon, total nitrogen, stable carbon isotope ratios, and grain size) and molecular-level (pigments, amino acids, fatty acids, and δ13C of individual fatty acids) analyses. Our results confirmed previous observations of a southwestward Rhodanian imprint in the nearshore sediments, with 97% of terrigenous inputs of organic matter near the river mouth. Isotopic values of bulk organic carbon, as well as fatty acid biomarkers and compound-specific δ13C signatures of most fatty acids clearly indicate that the Rhone inputs consist of a mixture of organic matter (OM) from different origins with a strong contribution from terrestrial sources (soil and plant debris), and a smaller input from freshwater microalgae, mostly diatoms. The influence of the Rhone River was prominent within the first ten kilometers, but may still be observed on the outer shelf (~21 km) as indicated by the occurrence of long chain fatty acids, which are derived from vascular plants, and their δ13C signatures. In the proximal prodelta, bacteria-specific fatty acids were abundant (1.65 mg g−1 OC at the mouth site) and were relatively depleted in δ13C confirming that bacteria mostly utilize land-derived OM. In the shelf area, the inputs of marine OM and its predominant utilization by the bacteria was confirmed, but the coupling between the pelagic and the benthic compartments appeared limited at this period of the year. Overall, degradation indexes based on amino acids (Dauwe's degradation index) and pigments (ratio of intact chlorophyll-a to the sum of chlorophyll-a + phaeopigment-a), as well as isotopic enrichment of source-specific fatty acids reveal an offshore gradient of OM decay reflecting the rapid deposition of the terrestrial material in the prodelta, the low mixing with OM deriving from marine sources and the efficient degradation of the OM. The OM delivered by the Rhone is relatively labile based on the intermediary value of Dauwe's degradation index, the high proportion of bio-available nitrogen and the occurrence of polyunsaturated fatty acids. Deltaic sediments off the Rhone River should thus be of sufficiently high nutritional quality to sustain dense macrofaunal communities.

title: Particle fluxes and geochemistry on the Canadian Beaufort Shelf: Implications for sediment transport and deposition
abstract: Biogeochemical data from four sequential sediment traps deployed for one full year (April 1987–March 1988) at the shelf edge (200 m isobath) of the Canadian Beaufort Sea are presented. In addition, multi-traps and Kenney traps, which collect material suspended near the bottom, provided data from the inner shelf for short intervals in spring and summer. A novel aspect of this work is the discrimination of biogenic and terrigenous contributions to the total carbon using a relationship between terrigenous carbon and aluminum (Al). The vertical flux in the Beaufort Sea derives primarily from three sources: marine biological production, the Mackenzie River Plume, and coastal and seabed erosion. The material trapped at all shelf edge sites was predominantly biogenic and the seasonal fluxes of both biogenic and terrigenous matter varied with geographical location. In open-water conditions, deposition of terrigenous material can be attributed at various times and places to (1) transport by the Mackenzie Plume to the shelf edge during freshet; (2) resuspension of sediment during north-westerly gales; and (3) erosion of steep coastlines during south-easterly gales followed by northward transport. On the west side of the shelf, the biogenic and terrigenous fluxes were highest in summer and were primarily influenced by the Mackenzie River freshet, increased solar flux, available nutrients, sea ice break-up, and water column stability. On the east side of the shelf, biogenic and terrigenous fluxes were highest in the fall and the most important controlling factors were the extensive open water, intense resuspension events accompanying storms from the northwest, and the flow of the fresh, warm, turbid waters of Mackenzie River to the northeast. There was strong evidence of sediment transport in mid-water and bottom layers, but the mechanisms involved cannot be inferred from this study. Stable isotopes of carbon and nitrogen, C/N ratios, biogenic silica, and chlorophyll a measurements help to distinguish between marine autotrophic production and heterotrophic production, of which the latter appears to dominate in the fall and continue beneath the ice into the polar night. Al and iron correlate strongly and are primarily associated with the terrigenous fraction whereas calcium and phosphorus have both terrestrial and biogenic associations.

title: Use of lipids and their degradation products as biomarkers for carbon cycling in the northwestern Mediterranean Sea
abstract: Changes in phytoplankton composition and degradation of particulate organic matter (POM) in the northwestern Mediterranean Sea were studied using time-series sediment trap samples collected during the spring of 2003 at the DYFAMED station. Lipid biomarkers (pigments, fatty acids, sterols, acyclic isoprenoids, alkenones and n-alkanols) were used to identify the main contributors to the POM produced during two phytoplankton blooms, while the effects of photooxidation, autoxidation and biodegradation were differentiated using characteristic lipid degradation products. Traps collected material corresponding to pre-bloom, bloom and post-bloom periods. Pigment analyses in the integrated (0-200 m) water column samples indicated that diatoms dominated the initial stages of the bloom event, with smaller amounts of haptophytes and pelagophytes. During the second part of bloom event there was a switch to haptophyte dominance with significant contributions from diatoms and pelagophytes, and an increased contribution from cryptophytes. Fatty acid distributions in the trap samples reflected contributions from marine bacteria, phytoplankton and zooplankton. Photooxidation and autoxidation products of monounsaturated oleic, cis-vaccenic and palmitoleic acids were detected along with photooxidation products from the chlorophyll side-chain. The relatively good correlation between the variation of U37K′ index and specific phytol autoxidation product percentage allowed us to attribute the alterations of U37K′ observed during the pre-bloom period and in the deeper traps to the involvement of selective autoxidative degradation processes. A variety of sterol oxidation products formed by biohydrogenation, autoxidation and photooxidation were detected. Sterol degradation products appeared to be less suited than oxidation products of monounsaturated fatty acids for the precise monitoring of the degradation state of POM, but their stable functionalized cyclic structure constitutes a useful tool to estimate the part played by biotic and abiotic processes. In these waters, biotic degradation generally predominates, but abiotic degradation is not negligible and, as expected, the extent of biotic degradation increases with depth. To obtain a more complete picture of POM degradation, the use of a pool of lipid degradation products (i.e. from unsaturated fatty acids, the phytyl side-chain and sterols) should be employed.

title: The fate of marine lipids: Biotic vs. abiotic degradation of particulate sterols and alkenones in the Northwestern Mediterranean Sea
abstract: Sterol and alkenone compositions in suspended particle and surface sediment samples collected in the Northwestern Mediterranean Sea during the MEDFLUX program were used to evaluate the relative importance of biotic and abiotic degradation processes on marine organic matter. Alkenone concentrations decreased much more rapidly (~ 500 fold) between 5 and 800 m than Δ 5 -sterols (~ 100-fold) or POC (~ 100-fold). The diverse functional groups attached to the stable tetracyclic carbon skeleton of Δ 5 -sterols appeared to be useful for estimating the relative effects of biotic vs. abiotic (photooxidation and autoxidation) degradation. Products of abiotic degradation predominated over products of biotic degradation in suspended particles in the NW Mediterranean. For alkenones, the U 37 K′ index increased from 0.43 to 0.55 with increasing water depth, and a good correlation between variations of U 37 K′ and concentrations of specific Δ 5 -sterol autoxidation products points to selective autoxidation of alkenones in suspended particles. Stereomutated alkenones (with cis double bonds) were detected in the surface sediment, allowing us to estimate that stereomutation resulted in a + 0.05 increase in U 37 K′ . Therefore, abiotic degradation may be another factor effect on alkenone-derived paleothermometry.

title: Degradation of particulate organic matter in the equatorial Pacific Ocean: Biotic or abiotic?
abstract: The behavior of organic matter (OM) in suspended and sinking particles in the equatorial Pacific Ocean was monitored by measuring lipid degradation products that are specific for biodegradation, photooxidation, and autoxidation. Photodegradation and autoxidation were significant for lipids associated with both suspended and sinking particles. Abiotically degraded terrestrial material strongly contributed to suspended particles and to sinking material in the deep ocean, probably as the result of incorporation of terrestrial particles into sinking aggregates. Analyses of degradation products of 24-methylcholesta-5,22-dien-3b-ol, 24-ethylcholest-5-en-3b-ol, and cholest-5-en-3b-ol gave diagnostic information concerning the differential behavior of phytoplanktonic, terrestrial, and zooplanktonic OM, respectively. Planktonic lipids were more susceptible to biodegradation than terrestrial lipids and biodegradation was more intense in sinking particulate organic matter (POM) than suspended POM, which we attribute to efficient transfer of singlet oxygen from suspended and senescent phytoplankton cells to associated bacteria and subsequent inhibition of heterotrophic degradation. There is a direct link between the photooxidation state of lipids of senescent phytoplankton cells in suspended particles and the apparent resistance of lipids toward biotic degradation. Terrigenous vascular plant OM, which is strongly autoxidized on land or in the atmosphere as it is transported to the remote ocean, is only weakly biodegraded during sedimentation in this open ocean setting. A significant increase in alkenone-based U K9 37 values (+0.07 equivalent to an inferred temperature change of +2uC) was observed in sinking particles with depth and the detection of epoxyalkenones further confirming the potential detrimental effect of aerobic bacterial degradation processes on the U K9 37 paleotemperature proxy.

title: A sediment and organic carbon budget for the Canadian Beaufort Shelf
abstract: The Arctic Ocean accounts for 20% of the world's continental shelves. Because the Arctic is sensitive to global change, budgets of organic carbon for its shelves are of immediate interest. The Mackenzie Shelf of the Canadian Beaufort Sea is the best North American proxy for the enormous Eurasian Shelves (large area, large river input), and the only site for which a complete organic carbon budget can be attempted, due to an extensive data base. A mass balance for the Mackenzie Shelf has been constructed for sediments, terrestrial organic carbon, and primary produced carbon. We have considered allochthonous inputs from the Mackenzie River, from coastal erosion, from smaller rivers, from groundwater, from the atmosphere and import by ice. The Mackenzie River dominates the supply to the Beaufort shelf of inorganic sediment (127 Mt a −1 ) and paniculate and dissolved terrestrial carbon (2.1 Mt a −1 POC, 1.3 Mt a −1 DOC). The combined input from all other sources contributes only about 5% of the Mackenzie load. Using sediment accumulation data we estimate that about half of the sediment supply is trapped in the delta, about 40% on the shelf and the remainder escapes the shelf edge by various processes. Autochthonous primary production in the delta and on the shelf adds a further 3.3 Mt a −1 of particulate organic carbon. A box model has been constructed to account for sediment, terrestrial organic carbon and primary produced carbon. Whereas about 60% of the terrestrial POC is preserved in delta and shelf sediments, it appears that most (97%) of the primary produced carbon is recycled and not preserved in sediments. Confidence in the budget should be improved by focusing future research on the determination of modern sedimentation rates on the delta and shelf, measurement of organic carbon content of deltaic sediments, determination of primary production on the shelf, and determination of the relative proportions of terrestrial and marine organic carbon preserved in sediments.

title: A circumpolar perspective on fluvial sediment flux to the Arctic ocean
abstract: Quantification of sediment fluxes from rivers is fundamental to understanding land-ocean linkages in the Arctic. Numerous publications have focused on this subject over the past century, yet assessments of temporal trends are scarce and consensus on contemporary fluxes is lacking. Published estimates vary widely, but often provide little accessory information needed to interpret the differences. We present a pan-arctic synthesis of sediment flux from 19 arctic rivers, primarily focusing on contributions from the eight largest ones. For this synthesis, historical records and recent unpublished data were compiled from Russian, Canadian, and United States sources. Evaluation of these data revealed no long-term trends in sediment flux, but did show stepwise changes in the historical records of two of the rivers. In some cases, old values that do not reflect contemporary fluxes are still being reported, while in other cases, typographical errors have been propagated into the recent literature. Most of the discrepancy among published estimates, however, can be explained by differences in years of records examined and gauging stations used. Variations in sediment flux from year to year in arctic rivers are large, so estimates based on relatively few years can differ substantially. To determine best contemporary estimates of sediment flux for the eight largest arctic rivers, we used a combination of newly available data, historical records, and literature values. These estimates contribute to our understanding of carbon, nutrient, and contaminant transport to the Arctic Ocean and provide a baseline for detecting future anthropogenic or natural change in the Arctic.

title: World-Wide Delivery of River Sediment to the Oceans
abstract: New data and new estimates from old data show that rivers with large sediment loads (annual discharges greater than about $$15 \times 10^{6}$$ tons) contribute about $$7 \times 10^{9}$$ tons of suspended sediment to the ocean yearly. Extrapolating available data for all drainage basins, the total suspended sediment delivered by all rivers to the oceans is about $$13.5 \times 10^{9}$$ tons annually; bedload and flood discharges may account for an additional $$1-2 \times 10^{9}$$ tons. About 70% of this total is derived from southern Asia and the larger islands in the Pacific and Indian Oceans, where sediment yields are much greater than for other drainage basins.

title: Sedimentation on the Canadian Beaufort Shelf
abstract: Modern sediment supply to the Beaufort shelf is dominated by the Mackenzie River which annually provides of the order of 1.25 × 108 tonnes a−1 of mainly fine grained sediment. Minor contributions of sediment are derived from other rivers, principally along the Yukon coast (1.5 × 106tonnes a−1) and from erosion of coastal bluffs (5.62 × 106tonnes a−1). Calculations of the sediment mass that has accumulated in the Mackenzie Delta and on the Beaufort Shelf during the Holocene suggests that sediment supply from the Mackenzie must have been higher during the earlier Holocene than it is today. Sea-ice covers the Beaufort Shelf from October to June each year. Ice scouring may be active during the winter, particularly below pressure ridges, but net transport by ice-keels is probably unimportant on the eastern shelf where sedimentation rates are relatively high. Ice scour transport and ice-rafting may be more important on the western shelf where sediment supply is much lower. Discharge and sediment supply from the Mackenzie River are both low during the winter months but rise rapidly in late April and May prior to break-up. A significant proportion of the sediment supply occurs before and during break-up, when open water is minimal. During the open water summer months, a surface plume of brackish water with relatively high concentrations of suspended sediment extends over much of the shelf, east of the delta. The position and dynamics of the plume is alternately controlled by the prevailing northwesterly or easterly winds, but net transport is to the east. The distribution of Holocene mud on the shelf reflects this transport and is closely matched to the maximum extent of the plume. Over the middle and outer shelf (20m water depth), wave motions influence bottom sediment transport less than 1% of the time. Near-bottom currents, weakly coupled to surface wind forcing, increase during storms and there is some evidence for resuspension of middle and outer shelf sediment during these events. In water depths less than 10 m, the influence of wave motion becomes important. Orbital wave motion combines with strong coastal currents during northwesterly storms to cause massive resuspensions of inner shelf sediments. Net transport during these events is generally parallel to the coast.

title: Coastal erosion vs riverine sediment discharge in the Arctic Shelf seas
abstract: This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45×106 t a–1) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10×106 t a–1, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4×106 t a–1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6×106 t a–1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10.

title: Modern terrigenous organic carbon input to the Arctic Ocean
abstract: The main objective of this chapter is to assess recent fluxes of terrigenous dissolved and particulate organic carbon into the Arctic Ocean. The most important terrigenous sources of organic matter (OM) in the ocean are (1) river and groundwater discharge, (2) coastal erosion, (3) sea-ice input and (4) aeolian material fluxes. The organic carbon fluxes of each of these pathways will be considered separately and a evaluation will be made of their roles in the total balance of OM input to the ocean.

title: Relative Contributions of Ice Algae, Phytoplankton, and Benthic Microalgae to Primary Production in Nearshore Regions of the Beaufort Sea
abstract: Phytoplankton, ice algae, and benthic microalgae are the three sources of primary production in the western Beaufort Sea in winter and spring. Phytoplankton levels in winter are low with chlorophyll a levels near the limit of detection. Microflagellates are the most abundant organisms present in the water column along with a few diatoms. Low chlorophyll a, standing stock, and primary productivity continue into June when the ice breaks up. Cells are present in sea ice from the time it forms in the fall and are generally scattered throughout the ice thickness. Microflagellates are the most abundant organisms, but some diatoms, mostly pennate species, are also present. Cells concentrate in the bottom few cm of ice during March-April in response to increasing light levels. Growth continues until late May-early June when maximum production and standing stock occur. Benthic microalgal production was barely detectable in spring although chlorophyll a levels were high, perhaps left from the previous production season. Light is apparently the major factor controlling production in the spring, with the ice algae being able to take advantage of increasing light levels early in spring. This community shades both the water column and benthos so that production in those habitats does not increase until after the ice algae disappear in early June, but the ice community may be inhibited by layers of sediment in the ice. During this study, the ice algae provided about two-thirds and the phytoplankton one-third of the spring primary production; the benthic community contribution was negligible.  Sea, phytoplankton, ice algae, benthic microalgae, primary productivity, chlorophyll a , standing stock, species present, environmental factors

title: Distribution patterns of Canadian Beaufort Shelf macrobenthos
abstract: Variation in macrofaunal composition in relation to sediment and water variables was analysed in nine regions of the western Canadian Arctic on the Beaufort Shelf and in Amundsen Gulf. We hypothesized that benthic community composition was distinctive (1) in a recurrent polynya in Amundsen Gulf and (2) in upwelling regions (Cape Bathurst and Mackenzie Canyon) and (3) changed in a linear gradient across the Beaufort Shelf. Analysis was based on 497 taxa > 0.4 mm from 134 samples at 52 stations sampled over 2002–4 in 11–1000 m water depth. Abundance ranged from 490.7 m− 2 in eastern Amundsen Gulf to 17,950 m− 2 off Cape Bathurst. (1) Community composition in Amundsen Gulf was not significantly different from the Beaufort Shelf at similar depth, indicating a lack of benthic effect of the polynya in Amundsen Gulf. (2) The Mackenzie Canyon macrofauna, although abundant and diverse, were similarly indistinct from the shelf community at similar depth. However, there was a 10-fold increase in inshore abundance in the upwelling region of Cape Bathurst due to large numbers of the amphipod Ampelisca macrocephala and the polychaete Barantolla americana, species that were not abundant elsewhere. (3) In the inshore fast ice and flaw lead regions of the Beaufort Shelf, under the influence of ice scour, storm effects, coastal erosion and the Mackenzie River, the macrofauna were dominated by the bivalve Portlandia arctica and the polychaete Micronephthys minuta. Offshore, where these influences were less and upwelling of deep Atlantic water occurred, the polychaete Maldane sarsi dominated. Faunal distribution across the Beaufort Shelf correlated with depth, water and sediment changes but was not significantly linear.

title: Foraminiferal assemblage changes over the last 15,000 years on the Mackenzie‐Beaufort Sea Slope and Amundsen Gulf, Canada: Implications for past sea ice conditions
abstract: Two cores, one from the Beaufort Sea Slope at 1000 m water depth (core 750) and one from the Amundsen Gulf at 426 m (core 124), were collected to help determine paleo–ice cover in the Holocene and late glacial of this area. Site 750 is particularly sensitive to changes in paleo–ice cover because it rests beneath the present ice margin of the permanent Arctic ice pack. Core 124 was sampled just in front of the former glacier that moved out into the Amundsen Gulf and started to recede about 13 ka B.P. Both cores have a strong occurrence of calcareous foraminifera in the upper few centimeters, but these disappear throughout most of the Holocene, suggesting more open water in that time period than present. In the sediments representing the end of the last glacial period (dated at ∼11,500–14,000 calibrated years B.P. (cal B.P.)) a calcareous fauna with an abundant planktic foraminiferal fauna suggests a return to almost permanent ice cover, much like the central Arctic today. Together with the foraminifera there was also abundant ice-rafted debris (IRD) in both cores between 12,000 cal B.P. and ∼14,000 cal B.P., but those units are of different ages between cores, suggesting different events. The IRD in both cores appears to have the same magnetic and chemical signals, but their origins cannot be determined exactly until clay mineralogy is completed. There is abundant organic debris in both cores below the IRD units: the organics in core 750 are very diffuse and not visually identifiable, but the organic material in core 124 is clearly identifiable with terrestrial root fragments; these are 14C dated at over 37,000 years B.P. This is a marine unit as it also has glacial front foraminifera in the sediment with the organic debris that must have been originating from subglacial streams. The seismic and multibeam data both indicate glaciers did not cross the core 124 site.

title: Characterisation of photo-oxidation and autoxidation products of phytoplanktonic monounsaturated fatty acids in marine particulate matter and recent sediments
abstract: Oxidation products of phytoplanktonic monounsaturated fatty acids have been detected in particulate matter and recent sediment samples collected at the SOFI station (Gulf of Fos, Mediterranean Sea). The fluxes of these compounds are not negligible and correspond to 0.14–0.03% of the total organic carbon flux in the zone investigated. Oxidation of monounsaturated fatty acids results mainly in the production of isomeric allylic hydroperoxyacids, which are relatively stable in the water column. Saturated hydroperoxyacids, epoxyacids and dihydroxyacids, deriving probably from the addition of hydroperoxides to the double bond of monounsaturated acids, have been detected also. During early diagenesis, hydroperoxides undergo heterolytic cleavage to aldehydes and ω-oxocarboxylic or ω-hydroxycarboxylic acids, or homolytic cleavage and subsequent transformation to the corresponding alcohols or ketones. Due to the good preservation of their distribution pattern in Recent sediments, isomeric allylic hydroxyacids thus formed will constitute more useful and specific tracers of oxidative processes than ω-oxocarboxylic or ω-dicarboxylic acids (with C9 as the predominant species). These compounds will allow easy differentiation between autoxidative and photooxidative processes and could thus provide a useful indication of the residence time of particulate organic matter in the water column, the physiological state of phytoplanktonic communities and current environmental problems related to ozone depletion.

title: A review of sterol markers for marine and terrigenous organic matter
abstract: 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 C 29 steranes need not indicate that most of the organic matter was derived from vascular plants.

title: Photoperoxidation of cholesterol in homogeneous solution, isolated membranes, and cells: comparison of the 5 alpha- and 6 beta-hydroperoxides as indicators of singlet oxygen intermediacy.
abstract: Singlet oxygen (1O2) can react with cholesterol (Ch) to give three possible ene-addition hydroperoxides: 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide (5 alpha-OOH), 3 beta-hydroxycholest-4-ene-6 alpha-hydroperoxide (6 alpha-OOH), and 3 beta-hydroxycholest-4-ene-6 beta-hydroperoxide (6 beta-OOH). The rates of dye-sensitized photogeneration and also the fates of 5 alpha-OOH and 6 beta-OOH in membrane bilayers have been studied and compared. Irradiation of unilamellar [14C]Ch/phospholipid vesicles in the presence of aluminum phthalocyanine tetrasulfonate or merocyanine 540 resulted in formation of 5 alpha-OOH and 6 beta-OOH, as determined by high performance liquid chromatography with radiochemical or electrochemical detection. The initial rate of 6 beta-OOH formation was 30-35% that of 5 alpha-OOH in a variety of liposomal systems. However, after a lag, 5 alpha-OOH invariably decayed via allylic rearrangement to 7 alpha-OOH (also known to be a free radical product), whereas 6 beta-OOH accumulated in unabated fashion until Ch depletion became limiting. Photooxidation of Ch in an isolated natural membrane (erythrocyte ghost) or in L1210 leukemia cells gave similar results. When the reaction was carried out in pyridine or methanol, the rate of 6 beta-OOH formation relative to 5 alpha-OOH was reduced by approximately half, with essentially no isomerization of the latter to 7 alpha-OOH.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Identification of a “pool” of lipid photoproducts in senescent phytoplanktonic cells
abstract: 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–C11 ω-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–C11 ω-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.

title: Lipids and their oxidation products as biomarkers for carbon cycling in the northwestern Mediterranean Sea: results from a sediment trap study
abstract: Classical lipid biomarkers (sterols, fatty acids and pigments) and their photo-oxidation and autoxidation products were measured in sediment trap samples collected during the summer of 1998 at the DYFAMED time-series station in the northwestern Mediterranean Sea to investigate changes in phytoplanktonic composition and alteration of particulate organic matter (POM). The study period covered a transitional situation from bloom event to oligotrophic conditions. At the beginning of the study, the phytoplankton community appeared to be mainly composed of diatoms, prymnesiophytes, pelagophytes and dinoflagellates. During the transition to the oligotrophic period, the contribution of small cells (pico- and nanoplankton) increased. Quantification of a “pool” of oxidation products resulting from photo-oxidation and autoxidation of phytoplanktonic sterols, monounsaturated fatty acids and chlorophyll phytyl side-chain provided very useful indications concerning the alteration state of POM during the investigated period. This “pool,” composed of some oxidation products which are very sensitive (but labile) indicators and of others which are less sensitive (but more refractory), allowed us to obtain a large range of diagnostic information about organic matter behaviour. Thanks to these indicators, visible light-induced and autoxidative degradative processes, which have been virtually ignored to date owing to the lack of suitable tracers, may be easily distinguished and appear to act intensively in the northwestern Mediterranean Sea.

title: Mechanisms of free radical oxidation of unsaturated lipids
abstract: The primary producs formed from the autoxidation of lipids can be understood based upon a mechanism that involves five different reaction types. These reactions are: reaction of a carbon radical and molecular oxygen, atom transfer of a hydrogen from substrate to the chain carrying peroxyl, fragmentation of the chain carrying peroxyl to give oxygen and a carbon radical, rearrangement of the peroxyl, and cyclization of the peroxyl. The mechanisms of these primary reaction steps has been the focus of extensive research over the past fifty years, and the current level of understanding of these transformations is the subject of this review.

title: Lipids in plants and microbes
abstract: 1 Introduction.- 1A General remarks.- 1B Classification of organisms.- 1C Lipid nomenclature.- 2 Major Lipid Types in Plants and Micro-Organisms.- 2A Fatty acids.- 2B Acyl lipids.- 2C Terpenoids.- 2D Sterols.- 2E Other lipid types.- 2F Ether lipids.- 3 Distribution of Lipids.- 3A Lipid distributions in different organisms and their use in taxonomy.- 3B Subcellular distribution of lipids.- 3C Intramembrane lipid distribution.- 3D Subcellular fractionation and membrane isolation.- 3E Factors affecting the lipid composition of plants and microorganisms.- 4 Biosynthesis.- 4A Fatty acids.- 4B Acyl lipids.- 4C Terpenoids and steroids.- 4D Complex lipids.- 4E Ether lipids.- 5 Degradation.- 5A Degradation of acyl lipids.- 5B Oxidation of fatty acids.- 6 Lipid Functions.- 6A Membrane structure and function.- 6B Storage.- 6C Microbial lipids as virulence factors.- 6D Conclusion.- Further reading.

title: Trans unsaturated fatty acids in bacteria
abstract: The occurrence oftrans unsaturated fatty acids as by-products of fatty acid transformations carried out by the obligate anaerobic ruminal microflora has been well known for a long time. In recent years, fatty acids withtrans configurations also have been detected in the membrane lipids of various aerobic bacteria. Besides several psychrophilic organisms, bacteria-degrading pollutants, such asPseudomonas putida, are able to synthesize these compoundsde novo. In contrast to thetrans fatty acids formed by rumen bacteria, the membrane constituents of aerobic bacteria are synthesized by a direct isomerization of the complementarycis configuration of the double bond without a shift of the position. This system of isomerization is located in the cytoplasmic membrane. The conversion ofcis unsaturated fatty acids totrans changes the membrane fluidity in response to environmental stimuli, particularly where growth is inhibited due to the presence of high concentrations of toxic substances. Under these conditions, lipid synthesis also stops so that the cells are not able to modify their membrane fluidity by any other mechanism.

title: Intense photooxidative degradation of planktonic and bacterial lipids in sinking particles collected with sediment traps across the Canadian Beaufort Shelf (Arctic Ocean)
abstract: The lipid content of seven samples of sinking particles collected with sediment traps moored at ~ 100 m depth in summer and fall across the Canadian Beaufort Shelf (Arctic Ocean) was investigated. Our main goal was to quantify and characterize the biotic and abiotic degradation processes that acted on sinking material during these periods. Diatoms, which dominated the phytoplanktonic assemblage in every trap sample, appeared to be remarkably sensitive to Type II (i.e. involving singlet oxygen) photodegradation processes in summer, but seemed to be relatively unaffected by biotic degradation at the same time. Hence, the relative recalcitrance of phytodetritus towards biodegradation processes during the Arctic midnight sun period was attributed to the strong photodegradation state of heterotrophic bacteria, which likely resulted from the efficient transfer of singlet oxygen from photodegraded phytoplanktonic cells to attached bacteria. In addition, the detection in trap samples of photoproducts specific to wax ester components found in herbivorous copepods demonstrated that zooplanktonic faecal material exported out of the euphotic zone in summer were affected by Type II photodegradation processes as well. By contrast, sinking particles collected during the autumn were not influenced by any light-driven stress. Further chemical analyses showed that photodegraded sinking particles contained an important amount of intact hydroperoxides, which could then induce a strong oxidative stress in underlying sediments.

title: Tracing the inputs and fate of marine and terrigenous organic matter in Arctic Ocean sediments: A multivariate analysis of lipid biomarkers
abstract: An understanding of the carbon cycle within arctic sediments requires discrimination between the terrigenous and marine components of organic carbon, insight into the removal mechanisms for labile carbon during burial and appreciation of shelf-to-basin processes. Using a large data set of multiple molecular organic markers (alkanes, alkanols, sterols, saturated and unsaturated fatty acids, dicarboxylic acids), we apply (1) principal components analysis (PCA) to obtain a robust comparison of biomarker compositions in Arctic Ocean sediments, (2) geometric mean (GM) linear regression of the PCA variables to estimate the relative contributions of labile/marine and stable/terrigenous sources to each biomarker and (3) the slope of the GM regression of each biomarker with TOC to provide a novel measure of the removal rate of each biomarker relative to phytol. The PCA- and TOC-based indices generally increase together: biomarkers with very high TOC-based removal rates such as the saturated and unsaturated n-alkanoic acids generally have a high labile/marine content from PCA, while the sterols have low removal rates, but exhibit a range of labile/marine content values and the n-alkanes and n-alkanols have low values for both. A dominant feature of all PCA models examined is a progressive decrease in the autochthonous/marine biomarkers with each increase in sediment core depth, which points to a universal diagenetic alteration of organic carbon with depth in the cores. The PCA model also displays a shelf to basin trend that is non-diagenetic and implies the ongoing (centuries or more) delivery of long-chain n-alkanes, n-alcohols and n-alkanoic acids in a matrix that is pre-formed and well-preserved within the sediments. Terrigenous biomarker distributions within the PCA model suggest that atmospheric transport of plant waxes in aerosols and the water borne transport of very fine plant macerals likely have significant roles in the export of these vascular plant biomarkers to the basins. Biomarker ratios and profiles of the PCA-based labile/marine content with core depth indicate that the PCA model is more strongly influenced by the biomarker lability than the marine content, while increases in the marine content are largely responsible for the shifts in composition for near-surface core sections.

title: Reactivity of recently deposited organic matter: Degradation of lipid compounds near the sediment-water interface
abstract: The usefulness of biomarker compounds buried in marine sediments depends upon a quantita tive understanding of the effects of early diagenesis on their distribution. To address this, a new experimental approach was utilized to determine rates of degradation in a coastal sediment. Rates of degradation for solvent-extractable lipid components were quantified in four sediment horizons composed of newly accumulated organic matter (31–144 days since deposition). Sediment accumulation rate data derived from changes in the inventory of Be-7 (t1/2 = 53.3 days) were combined with concentration data for lipid biomarker compounds, enabling us to evaluate the reactivity of organic matter in the upper 8 cm of the rapidly accumulating sediments of Cape Lookout Bight, North Carolina, USA (CLB). Net rates of loss and rate constants were calculated for individual compounds belonging to three classes of lipids: fatty acids, sterols, and n-alkanes. Individual components showed a range in reactivity, in some cases (fatty acids), attributable to differences in their biological sources. Rates and rate constants were consistently highest in the surficial sediments (0–2.5 cm), indicating that the reactivity of a given molecule(s) decreases over time, and beginning soon after deposition. Comparison with apparent rate constants (k′) calculated over longer timescales (one and ten years) shows that steady-state diagenetic models underestimate rates of degradation at or near the sediment-water interface by an order of magnitude.

title: Terrestrial and marine biomarkers in a seasonally ice-covered Arctic estuary — integration of multivariate and biomarker approaches
abstract: Hydrocarbons, including alkanes, alkenes, hopane triterpenes and polycyclic aromatic hydrocarbons (PAHs), plus sterols, n-alcohols and a number of higher plant triterpenoids have been determined for suspended particulate, sediment trap and sediment samples taken from the Mackenzie River and the adjacent Mackenzie shelf in the Beaufort Sea. These biomarkers are valuable tracers of terrigenous and petrogenic inputs from the river to the shelf water column and are also useful for assessing marine production in the Mackenzie River estuary. We use Principal Component Analysis (PCA) to provide a robust classification of biomarkers according to their primary source (e.g. terrigenous, marine) and to identify which biomarkers covary. 
 
The Mackenzie River is the dominant source for n-alkanes, n-alcohols, sterols and triterpenoids from higher plants, diagenetic hopanes, petrogenic isoprenoids and parent (unsubstituted) PAHs to the Mackenzie shelf. The riverine hydrocarbon signature of these markers is modified by preferential settling out of lithic material relative to less dense higher plant debris. Seasonal marine production of a suite of alkenes, sterols and alcohols from phytoplankton and Zooplankton is evident in water column and sediment trap samples, but these labile compounds tend not to be preserved in surficial sediments. Although few individual sterols provide unambiguous markers of terrestrial or marine organic matter, PCA successfully classifies sterols as either principally marine or principally terrestrial. n-Alcohols are often overlooked as biomarkers, but we find that they too reflect the relative contributions of Zooplankton and terrigenous inputs in the Mackenzie estuary. 
 
To quantify dispersal of riverine material on the adjacent shelf in the context of dilution by marine production, we develop a multivariate Partial Least Squares (PLS) path model. We find that the PLS results strengthen geochemical interpretations based on individual biomarkers by providing a quantitative representation of the differences among samples. PLS successfully models the increases in terrigenous particulate on the shelf with river flow and the effect of autochthonous production.

title: Organic geochemistry of particulate matter in the ocean: the role of particles in oceanic sedimentary cycles
abstract: Organic geochemists often use the occurrence of specific organic compounds in marine sediments as biomarkers to relate sedimentary organic matter to biological processes in the overlying water column. However, organic matter undergoes many diagenetic changes during transport through the water column. Only a small fraction of the organic matter produced in surface waters reaches the sea floor to be incorporated into the sediments. This material is subject to considerable transformation by heterotrophic organisms. The initial structures of individual compounds can be altered and the proportion of various compounds and compound classes can change as a result of varying stabilities. We summarize here the results of our studies of the organic geochemistry of suspended and sinking particles collected as part of the PARFLUX and VERTEX programs and present new results for amino acids, fatty acids, sterols and steroidal ketones from the VERTEX project site north of Hawaii.

title: Long-range transport of terrestrially derived lipids in aerosols from the south Pacific
abstract: Terrestrially produced participate organic matter can be transported relatively fast in the atmosphere, long distances over the ocean. It has been hypothesized that this atmospheric transport may be an important way of quickly introducing continentally-derived organic material to the surface waters of the open ocean1–11. After rapid transport through the water column to the sediment surface12, these terrestrial organic substances could account for an important fraction of the organic carbon found in the sedimentary record13. The atmospheric fluxes of these organic substances are large enough to have a major potential impact on the inventory of terrestrially derived lipid material, originating from vascular plant waxes, found in deep-sea sediments13. We present here the first use of organic compound biological source marker information in conjunction with long-range meteorological trajectory analysis to elucidate specific terrestrial source regions and to determine the transport pathways of organic material through the atmosphere to remote marine locations.

title: Comparative study of UV and visible light induced degradation of lipids in non-axenic senescent cells of Emiliania huxleyi
abstract: Irradiation of killed non-axenic cells of Emiliania huxleyi (Prymnesiophyceae) by PAR and UVR resulted in a strong photodegradation of most of the unsaturated lipid components (chlorophylls, unsaturated fatty acids and brassicasterol) of this haptophyte. This degradation, which mainly involves type II (i.e. singlet oxygen-mediated) photosensitized oxidation processes, was induced by both PAR and UVR. Alkenones were the sole unsaturated components of E. huxleyi unaffected by photodegradation processes. This particular recalcitrance was attributed to the trans configuration of their double bonds, which is less reactive toward singlet oxygen than the classical cis configuration of the double bonds of the other lipids. UVR exposure also induced photosensitized stereomutation (cis-trans isomerization) of the double bonds of some lipids (e.g. monounsaturated fatty acids and chlorophyll phytyl side-chain) and of some of their oxidation products affording (after reduction) some compounds (e.g. 9-hydroxyoctadec-cis-10-enoic and 10-hydroxyoctadec-cis-8-enoic acids arising from oleic acid oxidation and 11-hydroxyoctadec-cis-12-enoic and 12-hydroxyoctadec-cis-10-enoic acids arising from cis-vaccenic acid oxidation) sufficiently specific to act as tracers of UVR-induced photodegradation in situ. A strong photodegradation of specific bacterial monounsaturated fatty acids (e.g. cis-vaccenic and 11-MeC18:1 omega 12 acids) was also observed and attributed to the migration of singlet oxygen from phytodetritus to the attached heterotrophic bacteria.

title: Comparison of killing of gram-negative and gram-positive bacteria by pure singlet oxygen
abstract: Gram-negative and gram-positive bacteria were found to display different sensitivities to pure singlet oxygen generated outside of cells. Killing curves for Salmonella typhimurium and Escherichia coli strains were indicative of multihit killing, whereas curves for Sarcina lutea, Staphylococcus aureus, Streptococcus lactis, and Streptococcus faecalis exhibited single-hit kinetics. The S. typhimurium deep rough strain TA1975, which lacks nearly all of the cell wall lipopolysaccharide coat and manifests concomitant enhancement of penetration by some exogenous substances, responded to singlet oxygen with initially faster inactivation than did the S. typhimurium wild-type strain, although the maximum rates of killing appeared to be quite similar. The structure of the cell wall thus plays an important role in susceptibility to singlet oxygen. The outer membrane-lipopolysaccharide portion of the gram-negative cell wall initially protects the bacteria from extracellular singlet oxygen, although it may also serve as a source for secondary reaction products which accentuate the rates of cell killing. S. typhimurium and E. coli strains lacking the cellular antioxidant, glutathione, showed no difference from strains containing glutathione in response to the toxic effects of singlet oxygen. Strains of Sarcina lutea and Staphylococcus aureus that contained carotenoids, however, were far more resistant to singlet oxygen lethality than were both carotenoidless mutants of the same species and other gram-positive species lacking high levels of protective carotenoids.

title: Epoxyoctadecanoic acids in plant cutins and suberins
abstract: Three C 18 epoxy acids occur in plant cutins and suberins. 9,10-Epoxy-18-hydroxyoctadecanoic acid is a common constituent of both cutins and suberins whilst 9,10-epoxy-18-hydroxyoctadec-12-enoic acid is also present in some cutins. 9,10-Epoxyoctadecane-1,18-dioic acid occurs more commonly in suberins. Epoxy acids may comprise up to 60% of the total monomers obtained from some polymers. The epoxy compounds are readily converted into their corresponding alkoxyhydrin alkyl esters on depolymerization of cutin or suberin by alcoholysis. The chromatographic and MS properties of the alkoxyhydrin derivatives enable them to be readily distinguished from other cutin and suberin hydroxyfatty acids and to be used for the qualitative and quantitative determination of epoxy acids in the polymers.

title: Free radicals in organic chemistry
abstract: Partial table of contents: GENERAL CONCEPTS AND BASIC PRINCIPLES. Detection and Observation of Free Radicals. Radical Structure. Radical Stability. Reactivity of Free Radicals. Radical Kinetics.  Addition and Fragmentation Reactions. Reactions of Charged Radicals. Free Radicals in Biochemistry. APPLICATIONS IN SYNTHESIS. Functionalization of C-H Bond. Transformation of Functional Groups. Cyclization. Aromatic Substitution. Coupling Reactions. Free Radical Reactions in Industry.

title: Epoxidation of unsaturated fatty acids by a soluble cytochrome P-450-dependent system from Bacillus megaterium.
abstract: In previous publications from this laboratory we have described a soluble, partially purified cytochrome P-450-dependent monooxygenase complex that, in the presence of NADPH and O2, catalyzes the monohydroxylation of long chain fatty acids, alcohols, and amides at the omega -1, omega -2, and omega -3 positions. We have now found that this preparation catalyzes the epoxidation as well as the hydroxylation of palmitoleic acid and a variety of other monounsaturated fatty acids. The experimental results reported here strongly support the concept that both hydroxylation and epoxidation are catalyzed by an identical cytochrome P-450 complex utilizing the same active and binding sites. Furthermore, for saturating levels of these substrates, the rate-limiting step in oxygenation does not appear to involve substrate structure. Thus, although the position and geometry of the double bond may dramatically affect the rate of epoxidation relative to hydroxylation, the combined rate of substrate oxygenation is essentially a constant independent of this ratio. Finally, we propose and present evidence for an enzyme-substrate binding model that involves polar binding of the carboxyl terminus and strong hydrophobic binding and sequestering of the terminal methyl group of the fatty acid. The three methylene carbons adjacent to the methyl group are positioned in a set geometry around the active site but the midchain region of a monounsaturated fatty acid is relatively free to interact or bind loosely with the enzyme surface in a variety of conformations. Depending on fatty acid structure, one or more of these conformations can bring the unsaturated center close enough to the active site to permit epoxidation of the double bond.

title: Efficient epoxidation of unsaturated fatty acids by a hydroperoxide-dependent oxygenase.
abstract: Detergent-solubilized and partially purified soybean peroxygenase was shown to actively catalyze, in the presence of alkylhydroperoxides as co-substrates, the epoxidation of mono- and polyunsaturated fatty acids such as oleic and linoleic acids. Octadecenoic acids were found to be better substrates than shorter mono-unsaturated fatty acids (C16:1 or C14:1), but the position of their double bond (at positions 6, 9, or 11) had little effect on the rates of epoxidation. The peroxygenase exhibits a strong stereospecificity since octadecenoic acids with double bonds in trans-configuration were not epoxidized at detectable rates. Oxidation of linoleic acid yielded the two positional monoepoxide isomers and, as the minor product, the diepoxide. An important regioselectivity was, however, observed in this case; i.e. the unsaturation at position 9,10 was epoxidized preferentially to that at 12, 13. Oxidation of oleic acid in the presence of 18O-labeled hydroperoxy-linoleic acid revealed an incorporation of about 80% of the label into the epoxide ring. Products similar to those formed by the peroxygenase by epoxidation of unsaturated free fatty acids such as linoleic acid have been described as important metabolites (leukotoxins) in the defense of plants, e.g. in fungal agressions. This aspect underlines the physiological relevance of this new and potent catalytic activity of the peroxygenase.

title: Physiological Status and Community Composition of Microbial Mats of the Ebro Delta, Spain, by Signature Lipid Biomarkers
abstract: A bstractPhysiological status of microbial mats of the Ebro Delta (Tarragona, Spain) based on the extraction of lipids considered ``signature lipid biomarkers'' (SLB) from the cell membranes and walls of microorganisms has been analyzed. Data from a day–night cycle show significant differences in viable cells countings (PLFA cells counts) ranging from 1.5 × 1010 to 5.0 × 1010 cells g−1 of sediment. Minimum values were observed at 18:00 and 6:00, when physicochemical conditions change drastically. The diversity of the microbial community was assessed by GC/MS analysis of phospholipid fatty acids (PLFA). The ratio of PLFA, representative of Gram-negative bacteria, comprises 47.8% of the total PLFA of the microbial mat community. The remaining PLFA was representative of Gram-positive (10.0%), anaerobic (5.7%), and eukaryotic microorganisms (5.7%), and other common lipids. Two different approaches were used as a comparative study to assess the physiological status of the microbial mats. Two parameters (cyclopropane fatty acids/ω7c monoenoic fatty acids, and measurement of the trans/cis monoenoic PLFA ratio) showed a minimum at midnight, suggesting the highest microbial activity. Higher values were observed at 18:00 and 6:00, coinciding with lower PLFA cell counts.

title: The cis-trans isomerase of unsaturated fatty acids in Pseudomonas and Vibrio: biochemistry, molecular biology and physiological function of a unique stress adaptive mechanism.
abstract: Isomerization of cis to trans unsaturated fatty acids is a mechanism enabling Gram-negative bacteria belonging to the genera Pseudomonas and Vibrio to adapt to several forms of environmental stress. The extent of the isomerization apparently correlates with the fluidity effects caused, i.e. by an increase in temperature or the accumulation of membrane-toxic organic compounds. Trans fatty acids are generated by direct isomerization of the respective cis configuration of the double bond without a shift of its position. The conversion of cis unsaturated fatty acids to trans is apparently instrumental in the adaptation of membrane fluidity to changing chemical or physical parameters of the cellular environment. Such an adaptive mechanism appears to be an alternative way to regulate membrane fluidity when growth is inhibited, e.g. by high concentrations of toxic substances. The cis-trans isomerase (Cti) activity is constitutively present and is located in the periplasma, it requires neither ATP nor any other cofactor such as NAD(P)H or glutathione, and it operates in the absence of de novo synthesis of lipids. Its independence from ATP is in agreement with the negative free energy of the reaction. cti encodes a polypeptide with an N-terminal hydrophobic signal sequence, which is cleaved off during or shortly after the enzyme is transported across the cytoplasmic membrane to the periplasmic space. A functional heme-binding site of the cytochrome c-type was identified in the predicted Cti polypeptide and very recently, direct evidence was obtained that isomerization does not include a transient saturation of the double bond.

title: Regioselective cis-trans isomerization of arachidonic double bonds by thiyl radicals: the influence of phospholipid supramolecular organization.
abstract: Trans unsaturated fatty acids in humans may be originated by two different contributions. The exogenous track is due to dietary supplementation of trans fats and the endogenous path deals with free-radical-catalyzed cis-trans isomerization of fatty acids. Arachidonic acid residue (5c,8c,11c,14c-20:4), which has only two out of the four double bonds deriving from the diet, was used to differentiate the two paths and to assess the importance of a radical reaction. A detailed study on the formation of trans phospholipids catalyzed by the HOCH2CH2S* radical was carried out on L-alpha-phosphatidylcholine from egg lecithin and 1-stearoyl-2-arachidonoyl-L-alpha-phosphatidylcholine (SAPC) in homogeneous solution or in large unilamellar vesicles (LUVET). Thiyl radicals were generated from the corresponding thiol by either gamma-irradiation or UV photolysis, and the reaction course was followed by GC, Ag/TLC, and 13C NMR analyses. The isomerization was found to be independent of cis double bond location (random process) in i-PrOH solution. In the case of vesicles, the supramolecular organization of lipids produced a dramatic change of the isomerization outcome: (i) in egg lecithin, the reactivity of arachidonate moieties is higher than that of oleate and linoleate residues, (ii) in the linoleate residues of egg lecithin, the 9t,12c-18:2 isomer prevailed on the 9c,12t-18:2 isomer (3:1 ratio), and (iii) a regioselective isomerization of SAPC arachidonate residues occurred in the 5 and 8 positions. This effect of "positional preference" indicates that thiyl radicals entering the hydrophobic region of the membrane bilayer start to isomerize polyunsaturated fatty acid residues having the double bonds nearest to the membrane surfaces. We propose that arachidonic acid and its trans isomers can function as biomarkers in membranes for distinguishing the two trans fatty acid-forming pathways.

title: The kinetics of thiyl radical-induced reactions of monounsaturated fatty acid esters.
abstract: The time-dependent isomerizations and thiol additions of several Z- and E-monounsaturated fatty acid methyl esters catalyzed by alkanethiyl radicals during gamma-radiolysis of tert-butyl alcohol solutions are analyzed on the basis of the radiation chemical yield of radicals and established rate data. This provides room-temperature rate constants for the reversible thiyl addition. Within experimental errors, they do not depend on the double bond position in the alkyl chains. Particularly noteworthy is the very fast beta-elimination of thiyl radicals from alkyl radicals which carry a second beta-substituent. It is supported by additional evidence obtained with a radical clock methodology, and the large preference of fragmentation to the E-isomers is attributed to different barriers for the formation of the E- and Z-transition states from the equilibrium radical structure.

title: Conversion of cis unsaturated fatty acids to trans, a possible mechanism for the protection of phenol-degrading Pseudomonas putida P8 from substrate toxicity
abstract: A trans unsaturated fatty acid was found as a major constituent in the lipids of Pseudomonas putida P8. The fatty acid was identified as 9-trans-hexadecenoic acid by gas chromatography, argentation thin-layer chromatography, and infrared absorption spectrometry. Growing cells of P. putida P8 reacted to the presence of sublethal concentrations of phenol in the medium with changes in the fatty acid composition of the lipids, thereby increasing the degree of saturation. At phenol concentrations which completely inhibited the growth of P. putida, the cells were still able to increase the content of the trans unsaturated fatty acid and simultaneously to decrease the proportion of the corresponding 9-cis-hexadecenoic acid. This conversion of fatty acids was also induced by 4-chlorophenol in nongrowing cells in which the de novo synthesis of lipids had stopped, as shown by incorporation experiments with labeled acetate. The isomerization of the double bond in the presence of chloramphenicol indicates a constitutively operating enzyme system. The cis-to-trans modification of the fatty acids studied here apparently is a new way of adapting the membrane fluidity to the presence of phenols, thereby compensating for the elevation of membrane permeability induced by these toxic substances.

title: Solvent-tolerant bacteria for biotransformations in two-phase fermentation systems
abstract: Product removal from aqueous media poses a challenge in biotechnological whole-cell biotransformation processes in which substrates and/or products may have toxic effects. The assignment of an additional liquid solvent phase provides a solution, as it facilitates in situ product recovery from aqueous media. In such two-phase systems, toxic substrates and products are present in the aqueous phase in tolerable but still bioavailable amounts. As a matter of course, adequate organic solvents have to possess hydrophobicity properties akin to substrates and products of interest, which in turn involves intrinsic toxicity of the solvents used. The employment of bacteria being able to adapt to otherwise toxic solvents helps to overcome the problem. Adaptive mechanisms enabling such solvent tolerant bacteria to survive and grow in the presence of toxic solvents generally involve either modification of the membrane and cell surface properties, changes in the overall energy status, or the activation and/or induction of active transport systems for extruding solvents from membranes into the environment. It is anticipated that the biotechnological production of a number of important fine chemicals in amounts sufficient to compete economically with chemical syntheses will soon be possible by making use of solvent-tolerant microorganisms.

title: Phospholipid ester-linked fatty acid profile changes during nutrient deprivation of Vibrio cholerae: increases in the trans/cis ratio and proportions of cyclopropyl fatty acids
abstract: The phospholipid ester-linked fatty acids of 0-day-, 7-day-, and 30-day-starved cultures of Vibrio cholerae were compared. Statistically significant trends were noted in the fatty acid profiles as the cells starved. The amount of the cis-monoenoic fatty acids declined (e.g., 16:1 omega 7c: 0 day, 39%; 7 day, 18%; 30 day, 11%). In contrast, the saturated fatty acids, the cyclopropyl derivatives of the cis-monoenoic fatty acids, and trans-monoenoic fatty acids increased during starvation. For instance, the amounts of 16:1 omega 7t were: 0 day, 1%; 7 day, 13%; 30 day, 17%; which increased the trans/cis ratio for 16:1 omega 7 from 0.02 (0 day) to 0.70 (7 day) to 1.56 (30 day). This may be due to the reported high turnover rates of cis-monoenoic fatty acids of membrane phospholipids and the availability of enzymes for the metabolism of these isomers. During starvation-induced phospholipid loss, the cis-monoenoic fatty acids would, therefore, be preferentially utilized. The ability to either synthesize trans-monoenoic acids (which are not easily metabolized by bacteria) or modify the more volatile cis-monoenoic acids to their cyclopropyl derivatives may be a survival mechanism which helps maintain a functional (although structurally altered) membrane during starvation-induced lipid utilization. In addition, a trans/cis fatty acid ratio significantly greater than that reported for most bacterial cultures and environmental samples (less than 0.1) may be used as a starvation or stress lipid index. Such a ratio could help determine the nutritional status of ultramicrobacteria and other reported dormant cells in natural aquatic environments.(ABSTRACT TRUNCATED AT 250 WORDS)

title: Shifts in the structure of soil microbial communities in limed forests as revealed by phospholipid fatty acid analysis
abstract: The effects of lime and wood-ash on the microbial community structure were evaluated by analyzing the phospholipid fatty acid (PLFA) composition of soils from two areas in the south of Sweden. A pine forest was amended with lime or ash at two concentrations, and a spruce forest was limed at one concentration. The treatments were carried out 5–6 years before sampling and raised the pH from approx. 4.0 to values between 4.8 and 7.0. At both sites there was a difference in the PLFA composition between the treated plots and the controls. The changes found were similar at both sites and correlated to the pH changes. No difference was found between limed plots and those treated with wood-ash. The methyl-branched fatty acids i15:0, i16:0 and 10Me16:0, the monounsaturated fatty acids 16: 1ω 7t and 18: 1ω 9, the cyclopropane fatty acid cy 19:0, and the saturated fatty acid 20:0 were more abundant in the control plots. In the plots with the highest pH there was a three-fold increase in the fatty acid 16: lω 5. An increase was also found for the fatty acids i14:0, 16:lω9, 16:lω 7c, cy17:0, 18:lω 7 and 10Me18:0. No effect on 18:2ω6 was found. The changes in PLFA pattern indicated that the increased pH caused a shift in the bacterial community to more Gram-negative and fewer Gram-positive bacteria, while the amount of fungi was unaffected. The increase in 10Me18:0 in limed soils indicated an increase in actinomycetes.

title: The trans/cis ratio of unsaturated fatty acids is not applicable as biomarker for environmental stress in case of long-term contaminated habitats
abstract: Cis-trans isomerization of unsaturated fatty acids is a crucial adaptive reaction of Pseudomonas and Vibrio species to toxic organic compounds or other environmental stress factors. In order to test the long-term performance of this adaptive mechanism as well as to assess its application as biomarker for environmental contamination studies were performed in batch cultures and in continuously running sand columns, simulating long-term contamination with bisphenol A (BPA). In short-term grown batch cultures a high correlation between trans/cis ratio and added BPA concentration and toxicity was observed. In contrary, this did not occur in the case of long-term sand columns. An increase in trans/cis ratio of unsaturated fatty acids only appeared in a limited period of time. Afterwards the trans/cis ratio reached the values measured for non-stressed cultures. Cis-trans isomerization is only an urgent response mechanism that is later substituted by other adaptive mechanisms. Therefore, it can be concluded that the trans/cis ratio of unsaturated fatty acids was shown not to be an appropriate biomarker for durable stress in the environment.

title: Thiyl radicals in biosystems: effects on lipid structures and metabolisms
abstract: Thiyl radicals are intermediates of enzyme- and radical-driven biochemical processes, and their potential as reactive species in the biological environment has been somehow underestimated. From organic chemistry, however, it is known that thiyl radicals isomerize the double bonds of unsaturated fatty acids to a mixture with very dominating trans isomers. Recently, this reaction has been particularly studied for biosystems, focusing on the effect of thiyl radicals on the natural all-cis double bonds of unsaturated phospholipids, which undergo a conversion to the unnatural trans form. In this paper we report briefly the role of thiyl radicals in biosystems, describe the main features of the radical-induced cis-trans isomerization process under both in vitro and in vivo conditions, and reflect on some consequences for membrane structures, lipid metabolism and enzymatic reactions.

title: Experimental and field evidence for thiyl radical-induced stereomutation of alkenones and other lipids in sediments and seawater
abstract: Possible origins were investigated for unusual cis/trans alkenones previously identified after incubation of a marine haptophyte Emiliania huxleyi strain with bacterial consortia isolated from cyanobacterial microbial mats. Diunsaturated alkenones and alkenoates isolated from the strain were incubated in the presence of ethanethiol to examine whether double bond stereomutation (i.e., cis/trans equilibration without double bond migration) could be induced by thiyl radicals. Significant stereomutation was observed after 4–5 days of incubation. The reaction was strongly attenuated when incubation was carried out in the presence of a free radical quencher (2,4,6-tri-tert-butylphenol), confirming the involvement of a thiyl radical-dependent mechanism. Room temperature incubation of E. huxleyi in natural seawater amended with ethanethiol also resulted in stereomutation of the alkenones and a significant increase in the measured value for the palaeotemperature proxy

title: Induction of Methanethiol Production by Brevibacterium linens CNRZ 918
abstract: A non-inducing medium (NID) was defined for studying the induction of methanethiol production by Brevibacterium linens CNRZ 918. The lowest L-methionine concentration capable of inducing maximal methanethiol production by the cells was 7 mM. The peptides L-Ala-L-Met and L-Met-L-Ala induced greater methanethiol production than free L-methionine. D-Methionine, L-cysteine, S-methyl-L-cysteine and L-ethionine were poor inducers. Culture temperature affected the duration of induction. An Na+ concentration of 1 M in the culture medium led to maximal methanethiol production capacity of both cells and cell extracts. L-Methionine and L-ethionine were the best substrates for the crude soluble cells extract (with release of methanethiol and ethanethiol respectively). Neither the derivatives of L-methionine that acted as inducers, nor D-methionine, were substrates for demethiolation. Demethiolation activity of the crude extract was thermolabile, not stimulated by Na+ and strongly inhibited by Zn2+, Mn2+ and Cu2+. The shortest generation time obtained for B. linens CNRZ 918 in NID medium + L-methionine was 4 h at 26 °C. Only coccoid forms were present when the culture temperature was 30 °C. The presence of L-methionine in the medium favoured their appearance. The strain grew best in the presence of 1% NaCl but tolerated concentrations up to 15%. The induction of methanethiol production was due to the induction of L-methionine-γ-demethiolase. The level of induction was probably related to the intracellular concentration of L-methionine. The transport system of L-methionine by B. linens CNRZ 918 was constitutive and Na+ dependent.

title: Microbial cycling of volatile organic sulfur compounds
abstract: Microbial cycling of volatile organic sulfur compounds (VOSCs), especially dimethyl sulfide (DMS) and methanethiol (MT), is intensively studied because these compounds play an important role in the processes of global warming, acid precipitation, and the global sulfur cycle. VOSC concentrations in freshwater sediments are low due to the balance between the formation and degradation of these compounds. These reactions occur for the greater part at the oxic/anoxic interphase of sediment and water column. In contrast to marine ecosystems, where dimethylsulfoniopropionate is the main precursor of MT and DMS, in freshwater ecosystems, VOSCs are formed mainly by methylation of sulfide and to a lesser extent from the degradation of S-containing amino acids. One of the major routes for DMS and MT formation through sulfide methylation is anaerobic O-demethylation of methoxylated aromatic compounds. Inhibition studies have revealed that the major part of the endogenously produced MT and DMS is degraded anaerobically by methanogens. The major bacterial groups involved in formation and consumption of VOSCs are described.

title: Dimethylsulfoniopropionate: Its Sources, Role in the Marine Food Web, and Biological Degradation to Dimethylsulfide
abstract: The massive quantities of phytoplankton in the North Atlantic and Antarctic oceans producing dimethylsulfoniopropionate (DMSP) as an osmoprotectant, much of which is degraded by marine bacteria to dimethylsulfide (DMS), ensures an important role for both compounds in the global sulfur cycle. The closest to a comprehensive review on this topic is a book of symposium proceedings edited by Kiene et al. (75); the more recent developments related specifically to DMSP degradation by microbial communities are found elsewhere (68). This article is more comprehensive, as it includes some of the earlier literature in describing the sources of DMSP, its release and linkage to the marine (primarily microbial) food web and subsequent degradation via cleavage to DMS and acrylic acid or demethylation and demethiolation to methanethiol. 
 
 
DMS production from DMSP has long been associated with marine algae according to the following reaction (20, 22): 
 
 
 
 
(1) 
 
 
 
DMSP is a tertiary sulfonium compound produced in high concentration by certain species of marine algae and plant halophytes for the regulation of their internal osmotic environment (1, 41, 47, 120), although its role in plants remains unclear. This alga-associated, i.e., particulate DMSP (DMSPp), when released into the marine environment as dissolved DMSP (DMSPd), can serve as a link between primary production and the microbial population, as it is readily degraded by chemoheterotrophic bacteria (59). DMSP turnover usually exceeds DMS production in natural waters (60) because DMSP is also demethylated to 3-methiolpropionate, which can be further demethylated to 3-mercaptopropionate or demethiolated, releasing methanethiol (72, 118). These reactions will be discussed in more detail below. 
 
The biogeochemical significance of DMSP cleavage was first suggested in 1972, when DMS was found to be universally present in seawater and emitted at a significant rate to the atmosphere (87). It was proposed that DMS, rather than H2S from coastal waters and mud flats, was the missing gaseous sulfur compound needed to enable the steady-state flow of sulfur between marine and terrestrial environments, making DMS emissions a key step in the global sulfur cycle (87). Atmospheric H2S, which arises primarily from dissimilatory sulfate reduction in organic matter-rich environments, could never be measured in sufficient quantity to be the vehicle for transferring large quantities of sulfur from sea to air to land. The total annual flux of biogenic DMS released to the atmosphere ranges from 28 to 45 Tg of S year−1, at least 10-fold higher than from all other sources (Table ​(Table1).1). Recent, more comprehensive calculations of global annual DMS flux from the oceans gave values that ranged from 13 to 37 Tg of S year−1 (57). This sea-to-air flux represents about 50% of the global biogenic sulfur flux to the atmosphere (3). However, anthropogenic sulfur emissions dominate the sulfur flux, representing 80 to 90% of the input to the global sulfur cycle (12, 23, 88). 
 
 
 
TABLE 1. 
 
Estimates of natural emissions of organosulfur compoundsa 
 
 
 
The magnitude of the marine DMS emissions is all the more remarkable considering that over half of the DMSP released is demethylated (68) and that a significant fraction of the DMS is oxidized by bacteria in the water column before it can be released to the atmosphere (13, 64). While most of the biogenic sulfur emissions (primarily DMS) come from the oceans, those coming from salt marshes and coastal wetlands are many times higher on a unit area basis (112). DMS flux per unit area from these marine wetlands is also much higher than from any known terrestrial soil (2). The biogeochemical cycling of DMSP and its biological degradation products are shown in Fig. ​Fig.11. 
 
 
 
FIG. 1. 
 
Scheme representing the mechanisms of DMSP and DMS cycling in the marine water column and atmosphere. DMSO, dimethyl sulfoxide; CCN, cloud-condensing nuclei; MMPA, 3-methiolpropionate; β-HP, β-hydroxypropionate; 3-MPA, 3-mercaptopropionate; ...

title: Biological and Environmental Chemistry of DMSP and Related Sulfonium Compounds
abstract: and providing background and the latest research on the subject. DMSP and related sulfonium compounds are of interest to biological chemists because they are used by organisms to combat osmotic stres

title: Trans Fatty Acids in Membranes: The Free Radical Path
abstract: The double bond geometry of most of the naturally occurring unsaturated fatty acid residues is cis. Due to the relevance of fatty acids as structural components of cell membranes and as biologically active molecules, the change of the cis geometry means a change of the associated functions and activities. The finding that the cis to trans isomerization is effective in phospholipids by the intervention of radical species led to the discovery that there can indeed occur an endogenous formation of trans fatty acids, whose significance in biological systems started to be addressed with in vitro and in vivo studies. Studies of liposome models simulating the formation of isomerizing species and evaluating their ability to interact with the hydrophobic part of the membrane bilayer has contributed to the gain in knowledge of the fundamental features of the lipid isomerization in membranes. Further work is in progress for the identification of the real culprits of the in vivo lipid isomerization, and recent results are shown on oleic acid micelles, where •NO2 radicals are not able to induce double bond isomerization in comparison with amphiphilic thiol, such as 2-mercaptoethanol. H2S and sulfur-containing amino acid residues are two of the possible species involved in this process at a biological level. An update of the scenario of the geometrical isomerization in membranes by free radicals is provided, together with applications and perspectives in life sciences.

title: The ene reaction of singlet oxygen: kinetic and product evidence in support of a perepoxide intermediate
abstract: The ene reaction of singlet oxygen (1O2) was examined using time-resolved techniques and by an intramolecular trapping reaction. The Eyring activation parameters reveal that the rate of the ene reaction of 1O2 with simple olefins is controlled by ΔS‡. A description of the reaction co-ordinate accommodating our findings and the results of others is presented.

title: The supply and preservation of ancient and modern components of organic carbon in the Canadian Beaufort Shelf of the Arctic Ocean
abstract: The provenance of organic matter in sediments from the Mackenzie River and Beaufort Shelf was investigated using the stable carbon and radiocarbon isotopic compositions of bulk organic matter and the stable carbon isotopic compositions of individual organic compounds, including lignin-derived phenols and lipid-derived fatty acids. Most river suspended sediments and shelf surface sediments contained organic carbon characterized by highly depleted Δ14C values that were consistent with average radiocarbon ages exceeding 7000 years. The stable carbon isotopic signatures of lignin phenols were uniformly depleted (−25≥δ13C≥−32‰), indicating the predominant contributions of C3 vascular plant sources. The isotopic compositions of C14 and C16 fatty acids exhibited important contrasts between the river (−36‰ to −40‰) and shelf (−25‰ to −29‰) sediments that were consistent with contributions from freshwater algae and/or vascular plants in the former and marine phytoplankton in the latter. Using 14C isotopic mass balance, the abundances of modern and ancient organic matter were quantitatively constrained. The fate of organic matter in the Beaufort Shelf was explored by normalizing these abundances to the specific surface area of sediments. Ancient organic carbon, which may include old pre-aged soil material as well as fossil bitumen or kerogen, accounted for the majority (∼70%) of the particulate organic matter exported by the Mackenzie River and deposited in surface sediments of the Beaufort Shelf. Modern organic carbon accounted for ∼30% in both river and shelf sediments, with significant contributions from vascular plant-derived materials in both river and shelf samples and from marine algae in the shelf sediments. Respiration (and/or leaching) of particle-bound marine organic matter dominates the carbon metabolism in the Mackenzie Delta/Beaufort Shelf region. However, land-derived pools, including modern carbon derived from vascular plants as well as ancient carbon also appeared to undergo a degree of post-depositional degradation prior to burial in the shelf. These novel source apportionments are reflected in an updated carbon budget for the study area.

title: Characterization of seawater samples using chemometric methods applied to biomarker fatty acids
abstract: Dissolved and particulate fatty acids have been analyzed by gas chromatography and gas chromatography/mass spectrometry in microlayer and subsurface water samples from the open Mediterranean sea. Structural elucidation of these compounds was performed before and after derivatization with dimethyldisulfide (DMDS) by GC/MS analyses of the fatty acid methyl esters (FAMEs) and their methylthio derivatives to locate the double bond of the monounsaturated FAMEs. Several hundred data were analyzed using a statistical approach. A multivariate method, CFA (Correspondence Factorial Analysis), and a non-parametric procedure. HCC (Hierarchical Clustering Classification), were used together to investigate the planktonic and microbiological sources in order to further characterize our samples. These statistical treatments allowed us to distinguish different inputs in the dissolved and particulate material: esters in the particulate material showed a major phytoplanktonic input dominated by the presence of diatoms except in one sample where zooplankton prevailed. Higher amounts of C 15 and C 17 branched and monounsaturated FAMEs indicated a stronger bacterial fingerprint for the dissolved FAMEs. C 16:1 ω 10 , previously unreported in seawater displayed a similar statistical behavior as other bacterial FAMEs suggesting a microbial origin of this compound. Dissolved FAMEs extracted from acidified seawater and particulate esterified FAMEs showed similar composition.