Isotopic Composition Of Fatty Acids Research Articles

Combining isotopic and elemental tracers for enhanced sediment source partitioning in complex catchments

Sediment fingerprinting quantifies soil erosion processes by tracing sediment origins in water bodies. In this regard, several types of tracers have been used to discriminate different sediment sources. Stable isotopic composition of fatty acids is associated with land use/vegetation cover, while elemental composition is related to different mineralogy. Isotopic tracers are characterised by their isotopic ratio and total content, requiring specific fingerprinting models. Consequently, this has led to few studies combining elemental and isotopic tracers.In this context, our analysis explores merging isotopic and elemental tracers to identify sediment sources in an ungauged Mediterranean mountain catchment. This catchment features consistent lithology, seasonal streams, and a history of land use changes, shifting from rangelands to croplands for increased agricultural production and later reverting to natural revegetation due to mid-20th-century land abandonment. Achieving effective source discrimination in these intricate landscapes remains a significant challenge, emphasising the need for diverse tracer integration.To explore this possibility, we collected composite source samples from three distinct land uses: cropland, Mediterranean forest, and pine forest, as well as two geomorphic features: highly disturbed areas such as exposed subsoil and channel banks. By considering these diverse sampling locations, we aim to capture the variability in sediment sources within the catchment. Our dataset spans one full hydrological year, allowing us to analyse sediment dynamics throughout different seasons and hydrological events.First, the Conservative Balance (CB) method was applied to integrate isotopic ratio and total content of each fatty acid into a single weighted tracer. Combining the weighted fatty acid (WFA) with elemental composition tracers significantly enhanced source discrimination, underlining the utility of employing diverse tracers for challenging source discrimination.The apportionment results revealed that agriculture, channel banks, and subsoils were the primary contributors, accounting for an average contribution of 29%, 39%, and 30% across most seasons. In contrast, sediment sources characterised by more permanent vegetation cover and minimal human influence, such as pine afforestation and Mediterranean forest, exhibited negligible contributions. The findings indicate the substantial impact of agricultural practices in Mediterranean agroecosystems, especially during storm events, on catchment hydrodynamics and sediment export. Additionally, despite their limited coverage, degraded areas significantly contributed to overall sediment dynamics through severe soil loss.By unravelling the hydrological implications of these sediment sources, our study provides valuable insights into the interplay between land use, hydrological processes, and sediment dynamics in Mediterranean mountain catchments.

The influence of carbon limitation on growth of Heterosigma akashiwo: A case study in fatty acids composition

Heterosigma akashiwo is an algal blooms species, and thus selected as the target microalgae in this work. This study attempted to investigate the influence of carbon limitation on the growth of H. akashiwo. Experiments were carried out in CO2-unlimited and CO2-limited systems (both include three nutritional groups). The stable isotope signatures and compound-specific stable three nutritional groups carbon isotopic composition of fatty acids were measured. Here we hypothesized that the carbon limitation could lead to the enriched of stable isotope ratios in the H. akashiwo. The results showed that carbon limitation made δ13C and δ13CFAs values more and more enriched in H. akashiwo. δ13C values were enriched in normal group of H. akashiwo within CO2-limited. δ15N values were enriched in nitrogen deficiency of H. akashiwo within both CO2-unlimited and CO2-limited. Furthermore, compared with the exponential phase, the enriched in δ13C was detected during the stationary phase in H. akashiwo within CO2-limited. A total of 8 major FAs were detected in H. akashiwo. Within CO2-unlimited, nitrogen deficiency promoted the synthesis of 4 FAs (14:1n-5c, 16:0, 18:0 and 18:3n-6c) in exponential phase. Within CO2-limited, nitrogen deficiency promoted the synthesis of FAs 14:0, 16:0 and 18:3n-3c, while phosphorus deficiency promoted the synthesis of all 6 FAs in exponential phase. δ13CFAs of H. akashiwo within CO2-limited showed the valley values and were significantly greater than those within CO2-unlimited. Furthermore, δ13CFAs of stationary phase were greater than those of exponential phase. δ13C14:1n-5c in nitrogen deficiency were the highest of the three nutrient groups within CO2-unlimited. This may point out that δ13CFAs could become an indicator of marine phytoplankton blooms. Overall, the present study may provide a novel approach to investigate the physiology and lipid metabolism of H. akashiwo blooms by using stable isotope ratios coupled with FAs profiles.

Hydrogen and carbon isotope responses to salinity in greenhouse-cultivated mangroves

Paired hydrogen and carbon isotope ratios (2H/1H and 13C/12C) of mangrove lipids can be used to quantitatively reconstruct past salinity and 2H/1H ratios of environmental water, and in some cases precipitation rate. This approach is based on the observation that net 2H- and 13C-fractionation increases and decreases, respectively, with the salinity of environmental water. In order to better understand the mechanisms underlying these empirical observations and ultimately improve estimates of paleoprecipitation from the paired H and C isotope approach, we analyzed the isotopic composition of fatty acids from five species of mangroves cultivated in salinity treatments of 5–30 ppt (g/kg) for 3.5 years in a greenhouse. Decreased net 13C-fractionation with salinity in three mangrove species was attributed to increased water use efficiency and thus a 13C-enriched internal CO2 pool. Net 2H-fractionation decreased with salinity in three mangrove species, opposite to previous observations of mangroves growing along salinity gradients in lakes and estuaries. The difference between uncultivated and greenhouse-cultivated mangroves may result from variability of 2H/1H of environmental water in natural environments. In addition, decreased net 2H-fractionation with salinity could be due to temporal variability in 2H/1H of leaf water and timing of lipid production, and the use of stored carbohydrates in seeds. Due to the sensitivity of the salinity and 13C-fractionation relationship for calculating both salinity and water isotopes, optimization of mangrove lipid H and C isotopes as a paleohydrologic tracer may be best achieved through laboratory-based calibrations of the relationship between 13C-fractionation and salinity.

Holocene Precipitation Records from Inner Mongolia Derived from Hydrogen Isotope Compositions of Sediment Fatty Acids

ABSTRACTThe Inner Mongolian Plateau lies along the northern limit reached by the East Asian summer monsoon. This geographic setting makes it especially sensitive to environmental change and an excellent site for understanding Quaternary East Asian monsoon variability. In this study we present new results of hydrogen isotopic compositions of fatty acids extracted from sediments, which were used to construct Holocene paleoprecipitation (or moisture) changes in Northern China. The hydrogen isotopic composition (D/H ratio) of n-acids in the sedimentary sequence of the Duoerji peat, Inner Mongolia, was determined with gas chromatography and mass spectrometry. Changes in the precipitation from middle Inner Mongolia are recorded by the D/H ratio of n-C20, n-C22, n-C24, n-C26, n-C28 acids (δD). From 10–9 ka, the relatively high δD values indicate reduced precipitation in the Early Holocene. Subsequently, increased precipitation is reflected by reduced δD values from 9–5.5 ka. After 5.5 ka, gradually increasing δD values record an overall decrease in precipitation. The precipitation trends established for the Duoerji sequence are consistent with other major paleoclimate proxies in the East Asian monsoon region, especially with a distinct Holocene optimum of increased monsoonal activity from 9–5.5 ka. The δD resulting paleo-precipitation record clearly shows that the Holocene climate in Northern China is basically controlled by the insolation changes.

Assessing the metabolism of sedimentary microbial communities using the hydrogen isotopic composition of fatty acids

The hydrogen isotopic composition of fatty acids (FAs) has previously been shown to reflect the metabolism of microorganisms in pure culture, but has rarely been tested in the environment. Here, we report the abundance and hydrogen isotopic composition of polar lipid derived FAs extracted from surface sediments of the saline Lake Grevelingen (The Netherlands), at two different stations and during two seasons with oxic bottom water conditions during spring and hypoxic to anoxic conditions during late summer. These data are compared with the bacterial diversity revealed by 16S rRNA gene amplicon sequencing. All measured FAs were depleted in deuterium relative to the bottom water by 103‰ to 267‰. FAs associated with heterotrophic bacteria (i-15:0 and ai-15:0) showed the smallest fractionation (−103‰ to −185‰) while those derived from pelagic photoautotrophic phytoplankton (20:5) showed the largest fractionation (−230‰ to −267‰). Overall, the hydrogen isotope fractionation reflected in the majority of the more commonly occurring FAs (14:0, 16:0, 16:1ω7) is relatively large (−172‰ to −217‰). Together with the high relative abundance of the 20:5 FA, this suggests a substantial contribution from dead pelagic biomass settling from the water column to the sedimentary polar lipid derived FA pool and not from the in situ microbial communities. Therefore, the majority of the isotope signal in the fatty acids from surface sediments might not represent the general metabolism of the active sedimentary communities. Therefore, the input of pelagic biomass into sedimentary environments may bias the information contained in the hydrogen isotopic composition of FAs.

Deuterium depletion in the fatty acids from beef

We examined stable hydrogen (δD, ‰ relative to V-SMOW) and carbon isotopic compositions (δ 13 C, ‰ relative to V-PDB) of fatty acids extracted from beef, and compared them with those from feeds (mixtures of plant materials) for the cattle. The δD value of stearic acid in beef is similar to that in the feeds, whereas the palmitic and oleic acids in beef are both significantly depleted in D (by ca. 60‰) as compared with the corresponding acids in the feeds. On the other hand, these fatty acids in beef are enriched in 13 C (by up to 5.7‰) relative to the corresponding acids in the feeds. Thus, the isotopic compositions of fatty acids in beef are not identical to those in the feeds. These results suggest that fatty acids in beef are an admixture of fatty acids derived from de novo biosynthesis in the cattle and from the feeds, and may imply that a considerable D-depletion process (e.g., hydrogenation of feed-derived fatty acids and/or dehydrogenation–hydrogenation cycling) occur in the fatty acids of the cattle.

Seasonal changes in the D / H ratio of fatty acids of pelagic microorganisms in the coastal North Sea

Abstract. Culture studies of microorganisms have shown that the hydrogen isotopic composition of fatty acids depends on their metabolism, but there are only few environmental studies available to confirm this observation. Here we studied the seasonal variability of the deuterium-to-hydrogen (D / H) ratio of fatty acids in the coastal Dutch North Sea and compared this with the diversity of the phyto- and bacterioplankton. Over the year, the stable hydrogen isotopic fractionation factor ε between fatty acids and water (εlipid/water) ranged between −172 and −237 ‰, the algal-derived polyunsaturated fatty acid nC20:5 generally being the most D-depleted (−177 to −235 ‰) and nC18:0 the least D-depleted fatty acid (−172 to −210 ‰). The in general highly D-depleted nC20:5 is in agreement with culture studies, which indicates that photoautotrophic microorganisms produce fatty acids which are significantly depleted in D relative to water. The εlipid/water of all fatty acids showed a transient shift towards increased fractionation during the spring phytoplankton bloom, indicated by increasing chlorophyll a concentrations and relative abundance of the nC20:5 polyunsaturated fatty acids, suggesting increased contributions of photoautotrophy. Time periods with decreased fractionation (less negative εlipid/water values) can potentially be explained by an increased contribution of heterotrophy to the fatty acid pool. Our results show that the hydrogen isotopic composition of fatty acids is a promising tool to assess the community metabolism of coastal plankton potentially in combination with the isotopic analysis of more specific biomarker lipids.

Impact of metabolism and growth phase on the hydrogen isotopic composition of microbial fatty acids.

Microorganisms are involved in all elemental cycles and therefore it is important to study their metabolism in the natural environment. A recent technique to investigate this is the hydrogen isotopic composition of microbial fatty acids, i.e., heterotrophic microorganisms produce fatty acids enriched in deuterium (D) while photoautotrophic and chemoautotrophic microorganisms produce fatty acids depleted in D compared to the water in the culture medium (growth water). However, the impact of factors other than metabolism have not been investigated. Here, we evaluate the impact of growth phase compared to metabolism on the hydrogen isotopic composition of fatty acids of different environmentally relevant microorganisms with heterotrophic, photoautotrophic and chemoautotrophic metabolisms. Fatty acids produced by heterotrophs are enriched in D compared to growth water with εlipid/water between 82 and 359‰ when grown on glucose or acetate, respectively. Photoautotrophs (εlipid/water between −149 and −264‰) and chemoautotrophs (εlipid/water between −217 and −275‰) produce fatty acids depleted in D. Fatty acids become, in general, enriched by between 4 and 46‰ with growth phase which is minor compared to the influence of metabolisms. Therefore, the D/H ratio of fatty acids is a promising tool to investigate community metabolisms in nature.

Seasonal rainfall and Indonesian vegetation

Paleoclimate Both gradual and abrupt changes in rainfall—similar in many ways to those happening today—had dramatic effects on the vegetation of Indonesia over the past 25,000 years. Dubois et al. report that variations in the seasonality of rainfall there, and the resulting water stress during the dry season, caused large swings in the balance between grasslands and forests. Vegetation type depended more on the depth of seasonal dry cycles than on the amount of annual rainfall, they found. These results, obtained by analyzing the stable isotopic composition of fatty acids produced by vascular plants and preserved in marine sediments, reflect the importance of the monsoonal precipitation that's so vital to Indonesian agriculture and human well-being. Nat. Geosci. 10.1038/ngeo2182 (2014).

Prominent bacterial heterotrophy and sources of <sup>13</sup>C-depleted fatty acids to the interior Canada Basin

Abstract. In recent decades, the Canada Basin of the Arctic Ocean has experienced rapidly decreasing summer sea ice coverage and freshening of surface waters. It is unclear how these changes translate to deeper waters, particularly as our baseline understanding of organic carbon cycling in the deep basin is quite limited. In this study, we describe full-depth profiles of the abundance, distribution and carbon isotopic composition of fatty acids from suspended particulate matter at a seasonally ice-free station and a semi-permanently ice-covered station. Fatty acids, along with suspended particulate organic carbon (POC), are more concentrated and 13C-enriched under ice cover than in ice-free waters. But this influence, apparent at 50 m depth, does not propagate downward below 150 m depth, likely due to the weak biological pump in the central Canada Basin. Branched fatty acids have δ13C values that are similar to suspended POC at all depths and are more 13C-enriched than even-numbered saturated fatty acids at depths above 3000 m. These are likely to be produced in situ by heterotrophic bacteria incorporating organic carbon that is isotopically similar to total suspended POC. Below surface waters, there is also the suggestion of a source of saturated even-numbered fatty acids which could represent contributions from laterally advected organic carbon and/or from chemoautotrophic bacteria. At 3000 m depth and below, a greater relative abundance of long-chain (C20–24), branched and unsaturated fatty acids is consistent with a stronger influence of re-suspended sedimentary organic carbon. At these deep depths, two individual fatty acids (C12 and iso-C17) are significantly depleted in 13C, allowing for the possibility that methane oxidizing bacteria contribute fatty acids, either directly to suspended particulate matter or to shallow sediments that are subsequently mobilized and incorporated into suspended particulate matter within the deep basin.

New insights into the Early Neolithic economy and management of animals in Southern and Central Europe revealed using lipid residue analyses of pottery vessels

Analyses of organic residues preserved in ceramic potsherds enable the identification of foodstuffs processed in archaeological vessels. Differences in the isotopic composition of fatty acids allow differentiation of non-ruminant and ruminant fats, as well as adipose and dairy fats. This paper investigates the trends in milk use in areas where sheep and goats are dominant in the faunal assemblage and in some sites from the Linearbandkeramik culture. Sites include: Colle Santo Stefano, Abruzzo, Italy, and the Oldest to Young Linearbandkeramik sites of Zwenkau, Eythra and Brodau, Saxony, and Wang and Niederhummel, Bavaria, Germany. More than 160 potsherds were investigated including cooking pots, bowls, jars, and ceramic sieves. The lipid residues presented provide direct evidence for the processing of ruminant and non-ruminant commodities at Zwenkau and Eythra, despite the absence of faunal remains at the sites. No dairy residues were detected in potsherds from LBK sites, except in a ceramic sieve at Brodau. Lipids from non-ruminant and ruminant fats, including from dairy fats, were detected at the site of Colle Santo Stefano showing a reliance on dairy products during the first half of the sixth millennium at this site; where sheep and goats were the major domestic animals.

Carbon isotopic compositions of fatty acids from the Japan Sea and their inferred terrestrial palaeoenvironment in Late Pleistocene

Carbon isotopic compositions of fatty acids from the Japan Sea and their inferred terrestrial palaeoenvironment in Late Pleistocene

Hydrogen isotopic fractionation in lipid biosynthesis by H 2-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‰). H 2 of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H 2, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H 2, 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 H 2/CO 2 are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H 2 as a significant source of fatty acid hydrogen. Grown on either H 2/CO 2 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 C 14 to C 17 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 H 2-consuming bacterium ( Sporomusa sp.), but much greater than in most photoautotrophs.

Carbon isotopic characteristics and their genetic relationships for individual lipids in plants and sediments from a marsh sedimentary environment

The carbon isotopes of individual lipids in herbaceous plants and tree leaves in Ruoergai marsh were measured by the GC-IRMS analytical technique in order to understand the inherent relationships of carbon isotopes between sedimentary and plant lipids from typical marsh environment. The analytical results show that the carbon isotopic compositions of n-alkanes in different kinds of plants differ significantly. Mean d 13C values of n -alkanes in herbaceous plants (-32.2‰― −36.9‰) are 3.3‰ lower than those in woody plant ( −27.2‰― −35.0‰). The carbon isotopic compositions of fatty acids in organisms ( −30.3‰― −36.2‰) are very similar to those of n -alkanes and the δ 13 C values for unsaturated fatty acids are within the range of those for satu-rated fatty acids. The differences in δ 13 C values between plant lipids are obvious and range from 2.4‰ to 7.8‰. It is observed that the carbon isotopic compositions of sedimentary lipids are closely related to those of plant lipids. The carbon isotopic compositions ( −27.0‰― −36.9‰) of n-alkanes, ≥C 16 fatty acids, n -alkanols, sterols and n-alkanones in the sediments are similar to those of plant lipids and the carbon isotopic compositions of short-chain sedimentary lipids are similar to those of long-chain sedimentary homologues. These indicate that the sedimentary lipids are derived from high plants. However, the δ 13 C values of C 14:0 and C 15:0 fatty acids in the sediments are lighter than those of the same carbon number saturated homologues in plants, reflecting the genetic features partially derived from bacteria. These data provide scientific evidence for carbon isotope-applied research of individual lipids.

Assessment of the production of 13C labeled compounds from phototrophic microalgae at laboratory scale

An integrated process for the indoor production of 13C labeled polyunsaturated fatty acids (PUFAs) from Phaeodactylum tricornutum is presented. The core of the process is a bubble column photobioreactor operating with recirculation of the exhaust gas using a low-pressure compressor. Oxygen accumulation in the system is avoided by bubbling the exhaust gas from the reactor in a sodium sulfite solution before returning to it. To achieve a high 13C enrichment in the biomass obtained, the culture medium is initially stripped of carbon, and labeled 13CO 2 is automatically injected on-demand during operation for pH control and carbon supply. The reactor was operated in both batch and semicontinuous modes. In semicontinuous mode, the reactor was operated at a dilution rate of 0.01 h −1, resulting in a biomass productivity of 0.1 g l −1 per day. The elemental analysis of the inlet and outlet flows of the reactor showed that 64.9% of carbon was turned into microalgal biomass, 34.9% remained in the supernatant mainly as inorganic compounds. Only 3.8% of injected carbon was effectively fixed as the target labeled product (EPA). Regarding the isotopic composition of fatty acids, results showed that fatty acids were not labeled in the same proportion, the higher the number of carbons the lower the percentage of 13C. Isotopic composition of EPA ranged from 36.5 to 53.5%, as a function of the methodology used (GC–MS, EA–IRMS or gas chromatography–combustion–isotope ratio mass spectrometry (GC–IRMS)). The low carbon uptake efficiency combined with the high cost of 13CO 2 make necessary to redefine the designed culture system to increase the efficiency of the conversion of 13CO 2 into the target product. Therefore, the possibility of removing 12C from the fresh medium, and recovering and recirculating the inorganic carbon in the supernatant and the organic carbon from the EPA depleted biomass was studied. The inorganic carbon of the fresh medium was removed by acidification and stripping with N 2. The inorganic carbon of the supernatant was recovered also by acidification and subsequent stripping with N 2. The operating conditions of this step were optimized for gas flow rate and type of contactor. A carbon recovery step for the depleted biomass was designed based on the catalytic oxidation to CO 2 using CuO (10 wt.%) as catalyst with an oxygen enriched atmosphere (80% O 2 partial pressure). In this way, the carbon losses reduced an 80.2% and the efficiency of the conversion of carbon in EPA was increased to 19.5%, which is close to the theoretical maximum. Further increase in 13CO 2 use efficiency is only possible by additionally recovering other labeled by-products present in the biomass: proteins, carbohydrates, lipids, and pigments.

Isotopic composition of fatty acids of extremely piezophilic bacteria from the Mariana Trench at 11,000 m

Two extremely piezophilic bacteria, DB21MT-2 and DB21MT-5, isolated from sediments of the Mariana Trench at 11,000 m, were grown in the laboratory under low-temperature (10 jC) and high-pressure (70 MPa) conditions. Phospholipid esterlinked fatty acids (PLFA) were analyzed by gas chromatography/mass spectrometry (GC/MS) and isotopic compositions of individual fatty acids were determined by gas chromatography isotope ratio mass spectrometry (GC-IRMS) in order to determine isotopic fractionation effects during biosynthesis. The piezophiles are characterized by fatty acids with carbon chains ranging from 14 to 22 carbons in length and by the presence of abundant polyunsaturated fatty acids (PUFA). Fatty acids from each culture exhibit a wide range of isotopic compositions (d 13 C vs. Pee Dee Belemnite (PDB)). With two exceptions (C15:0 and C17:1 from DB21MT-2), all fatty acids are depleted in 13 C relative to that of bulk carbon in the bacterial growth substrate. In addition, strain DB21MT-2 shows systematically higher (less negative) d 13 C values than strain DB21MT-5. The implications for isotope fractionation in fatty acid biosynthesis and the interpretation of isotopic composition of sedimentary fatty acids are discussed. It is suggested that the same type of microorganisms could have rather different d 13 C under the same growth conditions, and that sedimentary fatty acids with distinct d 13 C values do not necessarily have to originate from different organisms. Interpretation of d 13 C values of sedimentary biomarkers may be complicated by such large variations in d 13 Co f

Carbon isotopic composition of fatty acids in the marine aerosols from the western North Pacific: implication for the source and atmospheric transport.

A combined molecular and isotopic approach was used in this study to reveal the source and transport of aerosols at a remote oceanic site. Fatty acid distributions and stable carbon isotopic compositions of individual fatty acids were determined in the aerosol samples collected at Chichi-Jima in the western North Pacific over a period of 41 months. Fatty acid concentration and isotopic composition delta13C (vs PDB) exhibited temporal variations. Concentrations of fatty acids (C12-C34) ranged from 7.6 to 20.7 ng/m3. The concentrations of lower molecular weight (LMW) fatty acids (C12 -C19) tend to decrease in winter and increase in summer, whereas the higher molecular weight (HMW) C20-34 fatty acids exhibited a reversed trend. Compound-specific isotopic analysis revealed that the LMW fatty acids exhibited consistently less negative delta13C values than the HMW fatty acids. However, both the LMW and HMW fatty acids displayed a similar trend of temporal variations in delta13C, suggesting thatthe fatty acids experienced similar atmospheric pathways and transport processes to the remote marine atmosphere, whereas the difference in absolute delta13C reflects the different sources of the fatty acids.

Fatty acid carbon isotope signatures in chemosynthetic mussels and tube worms from gulf of Mexico hydrocarbon seep communities

The δ 13C values of specific fatty acids isolated from mussels and two species of tube worm from Gulf of Mexico hydrocarbon seep communities show 13C depletion characteristic of a chemosynthetic food source. The carbon isotopic composition of fatty acids in Lamellibrachia and Escarpia-like tube worms ranged from −29.3‰ to −18.0‰ while the fatty acid C-isotopic composition in the methanotrophic mussel Bathymodiolus childressi ranged from −45.4‰ to−39.6‰ or from −78.8‰ to −68.4‰, depending upon whether thermogenic or biogenic methane was utilized by the methanotrophic symbionts. In most cases, unsaturated fatty acids were depleted relative to saturated fatty acids, indicating de novo transformations.Exceptions some unsaturated 18 carbon fatty acids, which were enriched relative to saturated acids of the same length indicating direct incorporation of the bacterial fatty acids by the host.

Isotopic composition and probable origin of individual fatty acids in modern sediments from Ruoergai Marsh and Nansha Sea, China

Carbon isotopic analyses of individual fatty acids in modern sediments from Ruoergai Marsh and Nansha Sea, China were undertaken to evaluate the biological sources of individual sedimentary fatty acids. The mean δ 13C values of individual fatty acids are −33.9‰ for Ruoergai Marsh and −29.3‰ for Nansha Sea, indicating different biological sources. The isotopic compositions of fatty acids of various chain lengths differ significantly, indicating that they have separate origins. The δ 13C values of long-chain saturated acids (≥C 20:0) from the two environments reflect a source from higher-land plants, whereas C 16:0 and C 18:0 acid values indicate an origin is from plankton for Nansha Sea samples and from higher-land plants for Ruoergai Marsh sample. The C 16:1 and C 18:1 monounsaturated acids in Nansha Sea samples probably have a common source as saturated fatty acids with the same carbon number, or are derived in part from a 13C-depleted source. Isotopic compositions of C 14:0 and C 15:0 acids in the two kinds of environments imply bacterial sources.

Isotopic compositions of lipid biomarker compounds in estuarine plants and surface sediments

We examined the isotopic compositions of fatty acids, sterols, and hydrocarbons isolated from three coastal macrophytes (Zostera marina, Spartina alterniflora, and Juncus roemerianus) in order to investigate the relative contribution of these vascular plants as sources of organic matter in coastal sediments such as Cape Lookout Bight, North Carolina. On average, lipid biomarker compounds extracted from the plants were depleted in 13C by 3–5‰ relative to δ13C total organic carbon (TOC). However, individual compounds within each lipid class varied by up to 5.6‰. Trends in the isotopic compositions of lipids were consistent with δ13CTOC; compounds obtained from Z. marina were the most enriched in 13C and those from J. roemerianus were the most depleted. The range in isotopic abundances and molecular compositions of the sediments was greater than that obtained from the plants, indicating that additional, presently unidentified sources of organic matter contribute to the Cape Lookout Bight sediments. Similarity between the signatures for suspended particulate matter and the sediments indicates that much of the sedimentary organic matter is derived from algal and bacterial sources. Bacterial sources of organic matter are likely greater during summer/early fall, and incorporation of 13C‐enriched bacterial biomass may contribute to observed seasonal shifts in δ13CTOC in the surficial sediments.