A quantitative study of the degradation of whale bone lipids: Implications for the preservation of fatty acids in marine sediments

The degradation and preservation affecting the biomarker record of ancient metazoa are not fully understood. We report on a five month experiment on the fate of fatty acids (FAs) during the degradation of recent whale vertebrae (Phocoena phocoena). Whale bones were analysed for extractable FAs and macromolecularly bound n-acyl compounds. Fresh bone showed extractable FAs dominated by 16:1ω7c, 16:0, 18:1ω9c and 18:0. Calculated degradation rate constant (k) values showed a rapid decrease in FA concentration, with k values higher for unsaturated than for saturated compounds (0.08/day for 18:1ω9c, 0.05/day for 16:0). The appearance or increased abundance of distinctive methyl branched (e.g. i/ai-15:0 and -17:0, 10Me-16:0) and hydroxy FAs (e.g. 10OH-16:0 and 10OH-18:0) were observed, providing clear evidence for the microbial degradation of bone organic matter and an input of lipids from specialised bacteria. Catalytic hydropyrolysis (HyPy) of demineralised extraction residues released up to 0.13% of the total n-C₁₆ and n-C₁₈ moieties in the degraded bones. This revealed that only a small, yet sizeable, portion of bone-derived fatty acyl units was sequestered into (proto)kerogen during the earliest stages of degradation.     

Biogeochemistry of particulate organic matter from lakes of different trophic levels in Switzerland

Biomarker compositions of particulate organic matter (POM) from the oligotrophic Lake Brienz and the eutrophic Lake Lugano (both Switzerland) are compared, in order to obtain information about organic matter (OM) production and transformation processes in relation to water column stratification. Eutrophic conditions in Lake Lugano are reflected by enhanced alkalinity, elevated total organic carbon (TOC) and chlorin contents compared with Lake Brienz. Lower δ¹³C values of dissolved inorganic carbon (DIC) in Lake Lugano reflect enhanced OM respiration in the water column.Differences in OM dynamics between both lakes, as well as seasonal variations, are evidenced by TOC-normalised concentration profiles of total fatty acids (FAs) and total neutrals. In Lake Brienz, the results reflect the relative contributions of primary productivity and refractory, allochthonous OM to POM, governed by particle load and interflows due to density stratification. The depth trends at Lake Lugano are a result of high primary productivity, water column stratification and associated particle load in the upper layers, as well as microbially induced degradation close to the chemocline and greater preservation under anoxic conditions. Minor differences exist with regard to the OM composition. In both lakes, FA distributions and the composition of n-alkanols indicate a predominant autochthonous OM source (algae, zooplankton, bacteria). Inputs of OM from diatoms are reflected in highly-branched isoprenoid (HBI) alkenes, 16:1 n-FAs and 24-methylcholesta-5,22-dien-3β-ol (either epibrassicasterol or brassicasterol). Differences in relative proportions of n-C₁₆ vs. n-C₁₈ FAs and alkanols, respectively, as well as in the percentages of C₂₇, C₂₈ and C₂₉ sterols relative to the sum of sterols are related to differences in the abundances of chrysophytes, diatoms and green algae within the euphotic zone of both lakes as well as in bacterial activity and soil in-wash. High relative proportions of cholesterol in the autumn samples, most pronounced at Lake Lugano, were attributed to an increased input from zooplankton grazing in the water column.Differences in OM degradation processes are reflected in slightly higher chlorin index values and higher relative proportions of saturated vs. unsaturated n-FAs in Lake Lugano. Higher contents of branched chain FAs, 16:1ω7 n-FA, and enhanced 18:1ω7/18:1ω9 n-FA ratios suggest enhanced bacterial biomass in the water column of Lake Lugano close to the chemocline. Increasing proportions of saturated n-FAs and n-alkanols with increasing water depth, most distinct in the autumn for both lakes, argue for intensified bacterial activity and degradation of OM during autumn. High relative contents of sterols and low n-alkanol concentrations in POM close to the chemocline at Lake Lugano during spring are interpreted to reflect higher primary productivity in the photic zone, OM export to the deeper parts and enhanced degradation rates of more labile constituents (i.e. C₁₃–C₂₀ n-alkanols), as compared to Lake Brienz.     

Gypsum-organic interactions in the marine environment: sorption of fatty acids and hydrocarbons

Free fatty acids make up the bulk (50–84% wt/wt) of lipid materials recovered from artificial gypsum precipitates and crystals collected from sea salt evaporation pans. Both the fatty acids and hydrocarbons associated with artificial gypsum tend to be of longer mean chain length than organic materials dissolved in the mother liquor. Increased specific adsorption of n-fatty acids at Ca²⁺ sites on gypsum surfaces is positively correlated with alkyl chain length. Neutral lipids were not significantly enriched in either type of gypsum precipitates. The fatty acids associated with gypsum from sea salt evaporation pans are branched fatty acids in contrast to the predominantly normal acids associated with artificial gypsum samples. Differences in the two adsorbed acid distributions are attributed to the unique lipids of hypersaline biota.     

Composition and origin of lipid biomarkers in the surface sediments from the southern Challenger Deep,Mariana Trench

The surface sediments collected from the southern Mariana Trench at water depths between ca. 4900 m and 7068 m were studied using lipid biomarker analyses to reveal the origin and distribution of organic matters. For all samples, an unresolved complex mixture (UCM) was present in the hydrocarbon fractions, wherein resistant component tricyclic terpanes were detected but C₂₇–C₂₉ regular steranes and hopanes indicative of a higher molecular weight range of petroleum were almost absent. This biomarker distribution patterns suggested that the UCM and tricyclic terpanes may be introduced by contamination of diesel fuels or shipping activities and oil seepage elsewhere. The well-developed faults and strike-slip faults in the Mariana subduction zone may serve as passages for the petroleum hydrocarbons. In addition, the relative high contents of even n-alkanes and low Carbon Preference Indices indicated that the n-alkanes were mainly derived from bacteria or algae. For GDGTs, the predominance of GDGT-0 and crenarchaeol, together with low GDGT-0/Crenarchaeol ratios (ranging from 0.86 to 1.64), suggests that the GDGTs in samples from the southern Mariana Trench were mainly derived from planktic Thaumarchaeota. However, the high GDGT-0/crenarchaeol ratio (10.5) in sample BC07 suggests that the GDGTs probably were introduced by methanogens in a more anoxic environment. Furthermore, the n-alkanes C₁₉–C₂₂ and the n-fatty acids C_20:0–C_22:0 were depleted in ¹³C by 3‰ compared to n-alkanes C₁₆–C₁₈ and the n-fatty acids C_14:0–C_18:0, respectively, which was interpreted to result from the preferential reaction of fatty acid fragments with carbon “lighter” terminal carboxyl groups during carbon chain elongation from the precursors to products. The abundance of total alkanes, carboxylic acids, alcohols and total lipids were generally increased along the down-going seaward plate, suggesting the lateral organic matter inputs play an important role in organic matter accumulation in hadal trenches. The extremely high contents of biomarkers in sample BC11 were most likely related to trench topography and current dynamics, since the lower steepness caused by graben texture and proximity to the trench axis may result in higher sedimentation rate. This paper, for the first time, showed the biomarker patterns in surface sediments of the Mariana Trench and shed light on biogeochemistry of the hardly reached trench environment.     

Mathematical modeling of the aquatic macrophyte inputs of mid-chain n-alkyl lipids to lake sediments: Implications for interpreting compound specific hydrogen isotopic records

We present a systematic study of chain-length distributions and D/H ratios of n-alkyl lipids (both n-alkanes and n-alkanoic acids) in a wide range of terrestrial and aquatic plants around and in Blood Pond, Massachusetts, USA. The primary goal is to establish a model to quantitatively assess the aquatic plant inputs of the mid-chain length n-alkyl lipids to lake sediments and to determine the average hydrogen isotopic ratios of these lipids in different plants. Our results show that middle-chain n-alkyl lipids (C₂₁-C₂₃n-alkanes and C₂₀-C₂₄n-alkanoic acids) are exceptionally abundant in floating and submerged aquatic plants, in contrast to the dominance of long-chain n-alkyl lipids (C₂₇-C₃₁n-alkanes and C₂₆-C₃₂n-alkanoic acids) in other plant types, which are consistent with previously published data from Mountain Kenya and the Tibetan Plateau. Combining available data in different environmental settings allows us to establish statistically robust model distributions of n-alkyl lipids in floating/submerged macrophytes relative to other plant types. Based on the model distributions, we established a multi-source mixing model using a linear algebra approach, in order to quantify the aquatic inputs of mid-chain n-alkyl lipids in lake sediments. The results show that ∼97% of the mid-chain n-alkyl lipids (C₂₃n-alkane and C₂₂n-acid (behenic acid)) in Blood Pond sediments are derived from floating and submerged macrophytes. In addition, D/H ratios of C₂₂n-acid and C₂₃n-alkane in the floating and submerged plants from Blood Pond display relatively narrow ranges of variation (−161 ± 16‰ and −183 ± 18‰, respectively). Our study demonstrates that mid-chain n-alkyl lipids such as C₂₃n-alkane and C₂₂n-acid could be excellent recorders of past lake water isotopic ratios in lakes with abundant floating and submerged macrophyte inputs.     

Organic matter from a sediment trap experiment in the equatorial north Atlantic: wax esters,steryl esters,triacylglycerols and alkyldiacylglycerols

The vertical flux and composition of wax esters, steryl esters, triacylglycerols, and alkyldiacylglycerols in particulate matter was determined in the equatorial Atlantic Ocean by deploying sediment traps at 389, 988, 3,755 and 5,068 m. Detailed compositional analyses of these lipids were carried out by high temperature glass capillary gas chromatography and gas chromatography/mass spectrometry.The distributions of these lipids are discussed in terms of potential biological sources. Zooplankton fecal matter and intact zooplankters may represent the most important input of these compounds to the shallower two traps, while the material in the deeper two traps appears to have been biogeochemically altered. The finding of these biochemically important compounds, often unsaturated, indicates that particle transit through the water column must be relatively fast.Wax esters were most abundant in the 389 m sediment trap and decreased with increasing trap depth. Compounds ranging from C₂₈–C₄₄ were present at all depths. The major homologs were C₃₂, C₃₄ and C₃₆, most often monounsaturated. The dominant alcohol/acid combinations in the 389 m trap were $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{14:0}}$ and $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{16:0}}$, but in the 988 m sample, $\text{C}{}_{\mathrm{16:0}}\text{C}{}_{\mathrm{18:1}}$ was the major wax ester. A flux maximum was observed for steryl esters at 988 m. Cholesteryl esters of C_14:0, C_16:1 and C_16:0, and $\text{C}{}_{\mathrm{18:1}}\text{C}{}_{\mathrm{18:0}}$ fatty acids were the dominant steryl esters. For triacylglycerols, fluxes in the 389 and 988 m traps were similar, while the deeper pair of traps contained much less triacylglycerol. C₄₆, C₄₈, C₅₀ and C₅₂ compounds were the major triacylglycerols. Constituent fatty acids in the 389 m and 988 m samples were mainly C_14:0, C_16:1, C_16:0, C_18:1 and C_18:0. In the 988 m material, C_20:5 and C_22:6 were also dominant. A homologous series of alkyldiacylglycerols was abundant in the 389 m trap material. The alkyldiacylglycerols consisted of C₄₆–C₅₆ compounds composed of C_16:0 alkyl moieties and C_14:0, C_16:0, C_18:1, and C_18:0 fatty acids.     

Seasonal changes in D/H fractionation accompanying lipid biosynthesis in Spartina alterniflora

To investigate potential variability in the biosynthetic fractionation of hydrogen isotopes between environmental water and plant lipids, the cord grass Spartina alterniflora was sampled from a single location in a coastal marsh over a period of 16 months. Values of δD for a variety of lipids were measured by gas chromatography/pyrolysis/isotope ratio mass spectrometry. S. alterniflora grows partially submerged in seawater, so it has a virtually unlimited supply of water with nearly unvarying isotopic composition. Temporal changes in the δD values of lipids can thus be interpreted as representing mainly variations in biosynthetic fractionation. Fatty acids, n-alkanes, and phytol extracted from S. alterniflora have nearly constant δD values from ∼October through May, but exhibit marked decreases of up to 40‰ during summer months. These shifts in lipid δD values are interpreted as representing a change in the source of organic substrates, principally acetate, used for their biosynthesis. Lower summertime δD values for lipids are consistent with an increasing reliance on current photosynthate as feedstock for biosynthesis, whereas stored carbohydrate reserves are utilized more extensively during other times of the year. Regardless of the specific mechanism, the data emphasize that overall fractionations between water and plant lipids depend on biological as well as environmental variables, and that the biosynthetic fractionation is not necessarily constant even for a single plant. Because lipids such as fatty acids are present in all cells and turn over on timescales of weeks to months, measurements of δD values in fatty acids may also provide useful constraints for distinguishing biologic versus environmental controls on cellulose δD values in trees.     

两种纯化方法获得脂肪酸的链长及碳同位素分布特征对比

饱和脂肪酸及其同位素组成是重建古环境和古气候的重要代用指标,目前存在多种提取及纯化流程。在全球变化研究中,基于不同原理的纯化流程得到的脂肪酸含量及其同位素组成是否一致,直接影响着该指标应用于不同区域重建结果的对比。本文用两种常见的脂肪酸纯化流程提取脂肪酸标准、现生植物和泥炭样品类脂物,通过对比发现:对脂肪酸标准两种流程都可以得到纯净的单体脂肪酸,而且回收率均较高(85%以上),都是较为可靠的脂肪酸纯化流程;然而对于天然样品,虽然高碳数脂肪酸(碳数>C₂₄)的回收率相近,流程1却能够获得相对较多的低碳数饱和脂肪酸,如泥炭样品中该流程获得的n-C₂₂脂肪酸是流程2的3倍;两种流程纯化狗尾草(Setaira viridis)和三叶草(Trifolium repens)得到n-C₁₆脂肪酸的δ¹³C不同,流程1分别为-21.1‰和-36.2‰;流程2分别为-23.3‰和-34.9‰,表明两个实验流程得到的低碳数脂肪酸的含量、脂肪酸链长分布模式以及碳同位素组成均存在明显的差异。实验结果显示,流程2分离纯化样品可得到几乎全部的游离态脂肪酸,而流程1可提纯样品中游离态和酯态存在的总脂肪酸。由于在沉积物中游离态脂肪酸和酯态脂肪酸可以相互转化,因此使用流程1分析样品中的总脂肪酸更为合适,也可以将类脂物皂化使酯态脂肪酸释放为游离态,然后使用流程2。     

Effects of oxygen and redox oscillation on degradation of cell-associated lipids in surficial marine sediments

Degradation patterns of sedimentary algal lipids were tracked with time under variable redox treatments designed to mimic conditions in organic-rich, bioturbated deposits. Uniformly ¹³C-labeled algae were mixed with Long Island Sound surface muddy sediments and exposed to different redox regimes, including continuously oxic and anoxic, and oscillated oxic: anoxic conditions. Concentrations of several ¹³C-labeled algal fatty acids (16:1, 16:0 and 18:1), phytol and an alkene were measured serially. Results showed a large difference (∼10×) in first-order degradation rate constants of cell-associated lipids between continuously oxic and anoxic conditions. Exposure to oxic conditions increased the degradation of cell-associated lipids, and degradation rate constants were positive functions (linear or nonlinear) of the fraction of time sediments were oxic. Production of two new ¹³C-labeled compounds (iso-15:0 fatty acid and hexadecanol) further indicated that redox conditions and oxic: anoxic oscillations strongly affect microbial degradation of algal lipids and net synthesis of bacterial biomass. Production of ¹³C-labeled iso-15:0 fatty acid (a bacterial biomarker) was inversely proportional to the fraction of time sediments were oxic, rapidly decreasing after 10 days of incubation under oxic and frequently oscillated conditions. Turnover of bacterial biomass was faster under continuously or occasionally oxic conditions than under continuously anoxic conditions. ¹³C-labeled hexadecanol, an intermediate degradation product, accumulated under anoxic conditions but not under oxic or periodically oxic conditions. The frequency of oxic: anoxic oscillation clearly alters both the rate and pathways of lipid degradation in surficial sediments. Terminal degradation efficiency and lipid products from degradation of algal material depend on specific patterns of redox fluctuations.     

Long-chain carboxylic acids in pyrolysates of Green River kerogen

Long-chain fatty acids (C₁₀-C₃₂), as well as C₁₄-C21 isoprenoid acids (except for C₁₈), have been identified in anhydrous and hydrous pyrolyses products of Green River kerogen (200–400°C, 2–1000 hr). These kerogen-released fatty acids are characterized by a strong even/odd predominance (CPI: 4.8-10.2) with a maximum at C₁₆ followed by lesser amounts of C₁₈ and C₂₂ acids. This distribution is different from that of unbound and bound geolipids extracted from Green River shale. The unbound fatty acids show a weak even/odd predominance (CPI: 1.64) with a maximum at C₁₄, and bound fatty acids display an even/odd predominance (CPI: 2.8) with maxima at C₁₈ and C₃₀. These results suggest that fatty acids were incorporated into kerogen during sedimentation and early diagenesis and were protected from microbial and chemical changes over geological periods of time. Total quantities of fatty acids produced during heating of the kerogen ranged from 0.71 to 3.2 mg/g kerogen. Highest concentrations were obtained when kerogen was heated with water for 100 hr at 300°C. Generally, their amounts did not decrease under hydrous conditions with increase in temperature or heating time, suggesting that significant decarboxylation did not occur under the pyrolysis conditions used, although hydrocarbons were extensively generated.     

Climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems: From soil water to speleothem calcite

Understanding the relationship between stable isotope signals recorded in speleothems (δ¹³C and δ¹⁸O) and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability. Here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open-closed conditions with respect to CO₂.The water entering the cave flows as a thin film towards the drip site. CO₂ degasses from this film within approx. 10 s by molecular diffusion. Subsequently, chemical and isotopic equilibrium is established on a time scale of several 10-100 s. The δ¹³C value of the drip water is mainly determined by the isotopic composition of soil CO₂. The evolution of the δ¹⁸O value of the carbonate species is determined by the long exchange time T_ex, between oxygen in carbonate and water of several 10,000 s. Even if the oxygen of the CO₂ in soil water is in isotopic equilibrium with that of the water, dissolution of limestone delivers oxygen with a different isotopic composition changing the δ¹⁸O value of the carbonate species. Consequently, the δ¹⁸O value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time.After the water has entered the cave, the carbon and oxygen isotope composition of the drip water may be altered by CO₂-exchange with the cave air. Exchange times, , of about 3000 s are derived. Thus, only drip water, which drips in less than 3000 s onto the stalagmite surface, is suitable to imprint climatic signals into speleothem calcite deposited from it.Precipitation of calcite proceeds with time constants, τ_p, of several 100 s. Different rate constants and equilibrium concentrations for the heavy and light isotopes, respectively, result in isotope fractionation during calcite precipitation. Since T_ex ? τ_p, exchange with the oxygen in the water can be neglected, and the isotopic evolution of carbon and oxygen proceed analogously. For drip intervals T_d < 0.1τ_p the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time. The calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water.For long drip intervals, when calcite is deposited from a stagnant water film, long drip intervals may have a significant effect on the isotopic composition of the DIC. In this case, the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval. Such processes must be considered when speleothems are used as proxies of past climate variability.     

Hydrogen-isotopic variability in lipids from Santa Barbara Basin sediments

We conducted an extensive survey of hydrogen-isotopic compositions (D/H ratios) of diverse sedimentary lipids from the Santa Barbara Basin (SBB), offshore southern California. The main goal of this survey was to assess the diversity of D/H ratios in lipids from marine sediments, in order to provide a more detailed understanding of relevant biological and geochemical factors impacting lipid isotopic variability. A total of 1182 individual δD values are reported from two stations in SBB, one located in the suboxic basin depocenter and the other on the fully oxic flank of the basin. Sediments collected from the basin depocenter span a depth of ∼2.5 m and reach the methanogenic zone. Lipids that were analyzed include n-alkanes, n-alkanols and alkenols, short- and long-chain fatty acids, linear isoprenoids, steroids, and hopanoids, and exhibit several systematic patterns. First, there are no significant differences in δD values between the two sampling locations, nor with increasing depth for most lipids, indicating that degradation does not influence sedimentary lipid δD values. Second, relatively large differences in δD values among differing molecular structures are observed in all samples. n-Alkyl lipids of probable marine origin have typical δD values between −150 and −200‰, those from terrestrial leaf waxes and aquatic plants range from −80 to −170‰, while petroleum n-alkanes are typically −90 to −150‰. Third, lipids inferred to derive from bacteria (branched fatty acids and hopanols) living at the sediment surface or in the water column tend to be D-enriched relative to similar algal products by 30‰ or more. At the same time, several other lipids have δD values that decrease strongly with depth, presumably as a result of in situ production by anaerobic bacteria. This dichotomy in isotopic compositions of bacterial lipids is inconsistent with a nearly constant D/H fractionation during lipid biosynthesis, and likely reflects significant variations associated with metabolism.     

Modelling carbon isotopes of carbonates in cave drip water

C isotopes in cave drip water are affected by both the C isotope composition of soil air and host rock carbonate. Furthermore, the C isotope composition of cave drip water strongly depends on the calcite dissolution system, i.e., open, closed and intermediate conditions. Here, we present a calcite dissolution model, which calculates the ¹⁴C activity and δ¹³C value of the dissolved inorganic carbon of the drip water. The model is based on the chemical equations describing calcite dissolution (). The most important improvement, relative to previous models, is the combination of the open and closed system conditions in order to simulate the C isotope composition during intermediate states of calcite dissolution and the application to carbon isotope measurements on cave drip waters from Grotta di Ernesto, Italy. The major changes in the C isotope composition of the drip water occur in response to variations in the open-closed system ratio. Additionally, the ¹⁴C activity and the δ¹³C value of the drip water depend on changes in the partial pressure of soil CO₂. Radiocarbon and δ¹³C values of the Grotta di Ernesto drip water are well reproduced by the model.     

Hydrogen isotopic fractionation in lipid biosynthesis by H2-consuming Desulfobacterium autotrophicum

We report hydrogen isotopic fractionations between water and fatty acids of the sulfate-reducing bacterium Desulfobacterium autotrophicum. Pure cultures were grown in waters with deuterium (D) contents that were systematically varied near the level of natural abundance (−37‰ ? δD ? 993‰). H₂ of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H₂, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H₂, and this reaction is conclusively shown to approach isotopic equilibrium. In addition, variation in the D/H ratio of growth water accounts for all variation in the hydrogen isotopic composition of fatty acids. The D/H ratios of fatty acids from cultures grown on H₂/CO₂ are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H₂ as a significant source of fatty acid hydrogen. Grown on either H₂/CO₂ or formate, D. autotrophicum produces fatty acids in which all hydrogen originates from water. For specific fatty acids, biosynthetic fractionation factors are mostly in the range 0.60 ? α_FA-water ? 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that α_FA-water generally increases with length of the carbon chain from C₁₄ to C₁₇ among both saturated and unsaturated fatty acids. These results indicate a net fractionation associated with fatty acid biosynthesis in D. autotrophicum that is slightly smaller than in another H₂-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs.     

Fractionation of carbon isotopes in biosynthesis of fatty acids by a piezophilic bacterium Moritella japonica strain DSK1

We examined stable carbon isotope fractionation in biosynthesis of fatty acids of a piezophilic bacterium Moritella japonica strain DSK1. The bacterium was grown to stationary phase at pressures of 0.1, 10, 20, and 50 MPa in media prepared using sterile-filtered natural seawater supplied with glucose as the sole carbon source. Strain DSK1 synthesized typical bacterial fatty acids (C_14-19 saturated, monounsaturated, and cyclopropane fatty acids) as well as long-chain polyunsaturated fatty acids (PUFA) (20:6ω3). Bacterial cell biomass and individual fatty acids exhibited consistent pressure-dependent carbon isotope fractionations relative to glucose. The observed Δδ_FA-glucose (−1.0‰ to −11.9‰) at 0.1 MPa was comparable to or slightly higher than fractionations reported in surface bacteria. However, bulk biomass and fatty acids became more depleted in ¹³C with pressure. Average carbon isotope fractionation (Δδ_FA-glucose) at high pressures was much higher than that for surface bacteria: −15.7‰, −15.3‰, and −18.3‰ at 10, 20, and 50 MPa, respectively. PUFA were more ¹³C depleted than saturated and monounsaturated fatty acids at all pressures. The observed isotope effects may be ascribed to the kinetics of enzymatic reactions that are affected by hydrostatic pressure and to biosynthetic pathways that are different for short-chain and long-chain fatty acids. A simple quantitative calculation suggests that in situ piezophilic bacterial contribution of polyunsaturated fatty acids to marine sediments is nearly two orders of magnitude higher than that of marine phytoplankton and that the carbon isotope imprint of piezophilic bacteria can override that of surface phytoplankton. Our results have important implications for marine biogeochemistry. Depleted fatty acids reported in marine sediments and the water column may be derived simply from piezophilic bacteria resynthesis of organic matter, not from bacterial utilization of a ¹³C-depleted carbon source (i.e., methane). The interpretation of carbon isotope signatures of marine lipids must be based on principles derived from piezophilic bacteria.     

Fatty acids of bacterial origin in contemporary marine sediments

Contributions by bacteria to recent sediments have been recognized as one important source of input for the extractable lipids. It has, however, proved difficult so far to conclusively relate the components identified to the contributing bacteria. This fact is primarily related to the lack of information on both the lipid chemistry of marine bacteria, and of detailed structures of the sedimentary lipids. In this paper a study of the fatty acids from a tropical marine sediment selected because of its high biomass content is reported, and relationships between the sedimentary extracts of the surface layer to fatty acid components of bacteria cultured from the sediment sample are detailed. By selecting specific structural features, a group of fatty acids have been identified as valid markers for bacteria in this environment: these include iso- and anteiso-branched chain acids; 10-methylpalmitic acid; cyclopropyl 17:0 and 19:0 acids of which ▽19:0 (11,12) is unique to bacteria; cis-vaccenic acid; and the 15:1, 17:1 ω6 and ω8 isomers especially when these occur in pairs; iso Δ7–15: 1 and iso Δ9–17:1 are branched unsaturated acids apparently unique to bacteria. Trans-monoene fatty acids are likely to be a direct bacterial input, and the hydroxy acids identified are probably of bacterial cell wall origin. This study, whilst emphasizing the necessity for detailed structural information on fatty acids in order to use them validly as biological markers, considerably extends the range of fatty acids as markers of bacterial input to contemporary sediments.     

Nature and dynamics of phosphorus-containing components of marine dissolved and particulate organic matter

The molecular sources, dynamics and analytical characterizations of the phosphorus (P) containing components of marine dissolved and particulate organic matter (OM) are reviewed. Using a combination of ¹³C and ³¹P nuclear magnetic resonance spectroscopy on samples collected from a depth profile (20-4000 m) at Station Aloha in the North Pacific subtropical gyre, the biomolecular associations of P functional groups in marine OM are identified. Compositional differences between ultrafiltered dissolved organic matter (UDOM; 1-100 nm size fraction) and ultrafiltered particulate organic matter (UPOM; 0.1-60 μm size fraction) as reflected by NMR and elemental analyses indicate that UDOM does not originate from simple solubilization of UPOM, and the aggregation of UDOM is not the primary source of UPOM. Regression analyses indicated a large fraction of the P in UDOM is associated with carbohydrates and amino acids, but not with lipids. Similar analyses for UPOM indicated that P is associated with carbohydrates, amino acids and lipids. The P functional groups also appear to be balanced in their distribution among molecular classes, because they remain in relatively constant proportion throughout the ocean.     

Short chain ladderanes: Oxic biodegradation products of anammox lipids

Anammox, the microbial anaerobic oxidation of ammonium by nitrite to produce dinitrogen gas, has been recognized as a key process in both the marine and freshwater nitrogen cycles, and found to be a major sink for fixed inorganic nitrogen in the oceans. Ladderane lipids are unique anammox bacterial membrane lipids that have been used as biomarkers for anammox bacteria in recent and past environmental settings. However, the fate of ladderane lipids during diagenesis is as of yet unknown. In this study, we performed oxic degradation experiments (at 20-100 °C) with anammox bacterial biomass to simulate early diagenetic processes occurring in the water column and at the sediment-water interface. Abundances of C₁₈ and C₂₀ ladderane lipids decreased with increasing temperatures, testifying to their labile nature. The most abundant products formed were ladderane lipids with a shorter alkyl side chain (C₁₄ and C₁₆ ladderane fatty acids), which was unambiguously established using two-dimensional NMR techniques on an isolated C₁₄-[3]-ladderane fatty acid. The most pronounced production of these short-chain lipids was at 40 °C, suggesting that degradation of ladderane lipids was microbially mediated, likely through a β-oxidation pathway. An HPLC-MS/MS method was developed for the detection of these ladderane alteration products in environmental samples and positively tested on various sediments. This showed that the ladderanes formed during degradation experiments also naturally occur in the marine environment. Thus, short-chain ladderane lipids may complement the original longer-chain ladderane lipids as suitable biomarkers for the detection of anammox processes in past depositional environments.     

Comparison of lipid character of sediments from the Great Lakes and the Northwestern Atlantic

Geolipid compositions of surficial sediments from Lake Michigan, Lake Huron, and from three locations in the Northwestern Atlantic were determined to compare source inputs and alteration processes in different sedimentary environments. Fatty acids, sterols, fatty alcohols, and alkanes were examined in both unbound and bound extracts of these samples. Significant amounts of long chain fatty acids, alcohols, and hydrocarbons are present in the deep ocean station, yet this location contains a proportionally larger amount of short chain geolipids than do marine stations closer to shore. Larger proportions of long chain lipids present in the Lake Michigan, Lake Huron, and Gulf of Maine samples relative to the open ocean samples reflect larger inputs of land-derived lipids to sediments closer to terrigenous sources. Marine samples contain a more complex mixture of sterols than is found in lake sediments, suggesting that sterol inputs and alteration processes in the marine environment are more complex than in lacustrine settings. Ratios of 16:1/16:0 and 18:1/18:0 fatty acids decrease with increasing distance from land, which suggests that fatty acid degradation before and during deposition becomes more extensive in the open deeper ocean stations.     

Controls on the age of vascular plant biomarkers in Black Sea sediments

Transfer of organic carbon (OC) from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport. Before transport, however, terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils. Using compound-specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated.Here we show compound-specific radiocarbon (¹⁴C) ages of terrigenous biomarkers and bulk ¹⁴C ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the Black Sea. ¹⁴C ages of long chain n-alkanes, long chain n-fatty acids and total organic carbon (TOC) are highest in front of the river mouths, correlating well with BIT (branched and isoprenoid tetraether) indices, which indicates contribution of pre-aged, soil-derived terrigenous organic matter. The radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter. Average terrestrial residence times of vascular plant biomarkers deduced from n-C₂₉₊₃₁ alkanes and n-C₂₈₊₃₀ fatty acids ages from stations directly in front of the river mouths range from 900 ± 70 years to 4400 ± 170 years. These average residence times correlate with size and topography in climatically similar catchments, whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the Black Sea catchment. Along-transect data imply petrogenic contribution of n-C₂₉₊₃₁ alkanes and input via different terrigenous biomarker transport modes, i.e., riverine and aeolian, resulting in aged biomarkers at offshore core locations. Because n-C₂₉₊₃₁ alkanes show contributions from petrogenic sources, n-C₂₈₊₃₀ fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers. Moreover, sedimentary n-C₂₈ and n-C₃₀ fatty acids appear clearly much less influenced by autochthonous sources than n-C₂₄ and n-C₂₆ fatty acids as indicated by increasing radiocarbon ages with increasing chain-length and are, thus, more representative as vascular plant biomarkers.