Biomarkers from individual carbonate phases of an Oligocene cold‐seep deposit,Washington State,USA

An Oligocene cold‐seep limestone (Lincoln Creek Formation, Washington State, USA) was studied for its lipid biomarker inventory. Biomarker analysis on minute amounts of sample (tens of mg) and complementary ¹³C_carbonate analyses allowed us to link biogeochemical processes with individual, closely intertwined carbonate phases. The ancient seep deposit exhibits four major carbonate phases, according to the paragenetic sequence of (I) micrite, (II) yellow aragonite, (III) clear aragonite and (IV) equant calcite spar. For the micrite, varying but significant amounts of archaea‐derived isoprenoids clearly indicate that the precipitation of this phase was induced by the microbial anaerobic oxidation of methane (AOM). However, water column‐derived lipids present in this carbonate phase reflect the incorporation of organic matter from background sediment cemented by authigenic micrite. Yellow aragonite made up only a minor rock component (<10% vol.), but contained a major portion of lipid biomarkers indicative of AOM. Along with low δ¹³C_carbonate values (less than ?30‰ Pee Dee Belemnite), this points to an intimate spatial association of AOM consortia with the precipitation of yellow aragonite. Clear aragonite showed similar δ¹³C_carbonate values but much lower, if any, contents of AOM biomarkers. This suggests that AOM‐derived carbonate ions diffused over a greater distance to the site of precipitation compared with yellow aragonite. The latest phase, equant calcite spar, did not yield appreciable biomarkers, but showed a notable ¹³C_carbonate‐enrichment that is most likely caused by methanogenesis that prevailed in the sediments after AOM activity had ceased. A comparison of the ancient seep carbonates with modern counterparts from Hydrate Ridge (offshore Oregon, USA) revealed a remarkable coincidence of the respective mineral phases and their biomarker patterns. This suggests that the mechanisms of carbonate formation and the associated biogeochemical processes remained unchanged over geological times. □Biomarkers, carbonates, cold seeps, Hydrate Ridge, isotopes, Oligocene, Washington.     

Interactive effects of elevated CO2 and nitrogen deposition on fatty acid molecular and isotope composition of above‐ and belowground tree biomass and forest soil fractions

Atmospheric carbon dioxide (CO₂) and reactive nitrogen (N) concentrations have been increasing due to human activities and impact the global carbon (C) cycle by affecting plant photosynthesis and decomposition processes in soil. Large amounts of C are stored in plants and soils, but the mechanisms behind the stabilization of plant‐ and microbial‐derived organic matter (OM) in soils are still under debate and it is not clear how N deposition affects soil OM dynamics. Here, we studied the effects of 4 years of elevated (¹³C‐depleted) CO₂ and N deposition in forest ecosystems established in open‐top chambers on composition and turnover of fatty acids (FAs) in plants and soils. FAs served as biomarkers for plant‐ and microbial‐derived OM in soil density fractions. We analyzed above‐ and belowground plant biomass of beech and spruce trees as well as soil density fractions for the total organic C and FA molecular and isotope (δ¹³C) composition. FAs did not accumulate relative to total organic C in fine mineral fractions, showing that FAs are not effectively stabilized by association with soil minerals. The δ¹³C values of FAs in plant biomass increased under high N deposition. However, the N effect was only apparent under elevated CO₂ suggesting a N limitation of the system. In soil fractions, only isotope compositions of short‐chain FAs (C₁₆₊₁₈) were affected. Fractions of ‘new’ (experimental‐derived) FAs were calculated using isotope depletion in elevated CO₂ plots and decreased from free light to fine mineral fractions. ‘New’ FAs were higher in short‐chain compared to long‐chain FAs (C_20?30), indicating a faster turnover of short‐chain compared to long‐chain FAs. Increased N deposition did not significantly affect the quantity of ‘new’ FAs in soil fractions, but showed a tendency of increased amounts of ‘old’ (pre‐experimental) C suggesting that decomposition of ‘old’ C is retarded by high N inputs.     

Environmental insights from high‐resolution (SIMS) sulfur isotope analyses of sulfides in Proterozoic microbialites with diverse mat textures

In modern microbial mats, hydrogen sulfide shows pronounced sulfur isotope (δ³⁴S) variability over small spatial scales (~50‰ over <4 mm), providing information about microbial sulfur cycling within different ecological niches in the mat. In the geological record, the location of pyrite formation, overprinting from mat accretion, and post‐depositional alteration also affect both fine‐scale δ³⁴S patterns and bulk δ³⁴S_pyrite values. We report μm‐scale δ³⁴S patterns in Proterozoic samples with well‐preserved microbial mat textures. We show a well‐defined relationship between δ³⁴S values and sulfide mineral grain size and type. Small pyrite grains (<25 μm) span a large range, tending toward high δ³⁴S values (?54.5‰ to 11.7‰, mean: ?14.4‰). Larger pyrite grains (>25 μm) have low but equally variable δ³⁴S values (?61.0‰ to ?10.5‰, mean: ?44.4‰). In one sample, larger sphalerite grains (>35 μm) have intermediate and essentially invariant δ³⁴S values (?22.6‰ to ?15.6‰, mean: ?19.4‰). We suggest that different sulfide mineral populations reflect separate stages of formation. In the first stage, small pyrite grains form near the mat surface along a redox boundary where high rates of sulfate reduction, partial closed‐system sulfate consumption in microenvironments, and/or sulfide oxidation lead to high δ³⁴S values. In another stage, large sphalerite grains with low δ³⁴S values grow along the edges of pore spaces formed from desiccation of the mat. Large pyrite grains form deeper in the mat at slower sulfate reduction rates, leading to low δ³⁴S_sulfide values. We do not see evidence for significant ³⁴S‐enrichment in bulk pore water sulfide at depth in the mat due to closed‐system Rayleigh fractionation effects. On a local scale, Rayleigh fractionation influences the range of δ³⁴S values measured for individual pyrite grains. Fine‐scale analyses of δ³⁴S_pyrite patterns can thus be used to extract environmental information from ancient microbial mats and aid in the interpretation of bulk δ³⁴S_pyrite records.     

Lipid biomarkers in ooids from different locations and ages: evidence for a common bacterial flora

Ooids are one of the common constituents of ancient carbonate rocks, yet the role that microbial communities may or may not play in their formation remains unresolved. To search for evidence of microbial activity in modern and Holocene ooids, samples collected from intertidal waters, beaches and outcrops in the Bahamas and in Shark Bay in Western Australia were examined for their contents of lipid biomarkers. Modern samples from Cat and Andros islands in the Bahamas and from Carbla Beach in Hamelin Pool, Western Australia, showed abundant and notably similar distributions of hydrocarbons, fatty acids (FAs) and alcohols. A large fraction of these lipids were bound into the carbonate matrix and only released on acid dissolution, which suggests that these lipids were being incorporated continuously during ooid growth. The distributions of hydrocarbons, and their disparate carbon isotopic signatures, were consistent with mixed input from cyanobacteria together with small and variable amounts of vascular plant leaf wax [C₂₇–C₃₅; δ¹³C ?25 to ?32‰Vienna Pee Dee Belemnite (VPDB)]. The FAs comprised a complex mixture of C₁₂–C₁₈ normal and branched short‐chain compounds with the predominant straight‐chain components attributable to bacteria and/or cyanobacteria. Branched FA, especially 10‐MeC₁₆ and 10‐MeC₁₇, together with the prevalence of elemental sulfur in the extracts, indicate an origin from sulfate‐reducing bacteria. The iso‐ and anteiso‐FA were quite variable in their ¹³C contents suggesting that they come from organisms with diverse physiologies. Hydrogen isotopic compositions provide further insight into this issue. FAs in each sample show disparate δD values consistent with inputs from autotrophs and heterotrophs. The most enigmatic lipid assemblage is an homologous series of long‐chain (C₂₄–C₃₂) FA with pronounced even carbon number preference. Typically, such long‐chain FA are thought to come from land plant leaf wax, but in this case, their ¹³C‐enriched isotopic signatures compared to co‐occurring n‐alkanes (e.g., Hamelin Pool TLE FA C₂₄–C₃₂; δ¹³C ?20 to ?24.2‰ VPDB; TLE n‐alkanes δ¹³C ?24.1 to ?26.2 ?‰VPDB) indicate a microbial origin, possibly sulfate‐reducing bacteria. Lastly, we identified homohopanoic acid and bishomohopanol as the primary degradation products of bacterial hopanoids. The distributions of lipids isolated from Holocene oolites from the Rice Bay Formation of Cat Island, Bahamas were very similar to the beach ooids described above and, in total, these modern and fossil biomarker data lead us to hypothesize that ooids are colonized by a defined microbial community and that these microbes possibly mediate calcification.     

Biosignatures present in a hydrothermal massive sulfide from the Mid-Atlantic Ridge

Mid‐ocean spreading and accompanying hydrothermal activities result in huge areas with exposure of minerals rich in reduced chemicals – basaltic and peridotitic rocks as well as metal sulfide precipitates – to the oxygenated seawater. Oxidation of Fe and S present in these rocks provides an extensive long‐term source of energy to lithotrophs. Investigation of lipid biomarkers and their carbon isotope ratios from a massive iron sulfide of an inactive sulfide mound or inactive chimney sampled at the western flank of the Turtle‐Pits hydrothermal field (Mid‐Atlantic Ridge, 5°S) revealed a unique lipid distribution. The bacterial fauna appears to be dominated by chemolithotrophs with a distinct lipid composition mainly comprising of iso‐branched fatty acids and nonisoprenoidal dialkyl glycerol diethers partially including the very rare macrocyclic cores with 30–35 carbon atoms (including 13,16‐dimethyloctacosane and 5,13,16‐trimethyloctacosane). The Bacteria are accompanied by most likely hydrogen/CO₂‐dependent methanogenic Archaea (e.g. Methanococcus) as well as other Archaea with a different life style (e.g. Ferroplasma). Alike some of the bacterial lipids the archaeal lipids predominantly consist of macrocyclic diethers including one C₄₀ and one C₄₁ isoprenoid. Structural homologues of the latter are so far only reported from a methanogenic archaeum and a Pleistocene sulfur deposit. Compound‐specific analyses of the stable isotope ratios revealed δ¹³C values for the majority of bacterial and archaeal lipid components of about 0‰ (vs. VPDB), indicative for chemolithoautotrophically fixed carbon which is, for distinct pathways, accompanied by only negligible fractionations. However, the presence of methanogenic Archaea is indicated by ¹³C‐depleted isoprenoidal lipids (δ¹³C ~ –50‰) characteristic for certain CO₂‐reducing methanogens synthesizing lipids via acetyl CoA.     

Anaerobic and Aerobic Oxidation of Methane at Late Cretaceous Seeps in the Western Interior Seaway,USA

The Late Cretaceous (Campanian) Tepee Buttes represent a series of conical, fossiliferous limestone deposits embedded in marine shales that deposited in the Western Interior Seaway. The previously suggested origin of the Tepee Buttes at methane-seeps was confirmed by this study. δ¹³C values as low as ?50‰ of early diagenetic carbonate phases of two Tepee Buttes near Pueblo (Colorado) reveal that methane was the major carbon source. Molecular fossils released from a methane-seep limestone contain abundant ¹³C-depleted archaeal lipids (PMI, biphytane; δ ¹³C: ?118 and ?102‰), derived from anaerobic methanotrophs. A suite of ¹³C-depleted bacterial biomarkers (branched fatty acids; ?73 to ?51‰) reflects the former presence of sulfate-reducing bacteria, corroborating that a syntrophic consortium of archaea and bacteria mediating anaerobic oxidation of methane already existed in Cretaceous times. Molecular fossils also suggest that methane was not exclusively oxidized in an anaerobic process. A series of unusual C₃₄/C₃₅-8,14-secohexahydrobenzohopanes with low δ¹³C values (?110 and ?107‰) points to the presence of aerobic methanotrophic bacteria at the ancient seep site.     

Microbiological and isotopic geochemical investigation of Lake Kislo-Sladkoe,a meromictic water body at the Kandalaksha Bay shore (White Sea)

Microbiological, biogeochemical, and isotopic geochemical investigation of Lake Kislo-Sladkoe (Polusolenoe in early publications) at the Kandalaksha Bay shore (White Sea) was carried out in September 2010. Lake Kislo-Sladkoe was formed in the mid-1900s out of a sea gulf due to a coastal heave. At the time of investigation, the surface layer was saturated with oxygen, while near-bottom water contained sulfide (up to 32 mg/L). Total number of microorganisms was high (12.3 × 10⁶ cells/mL on average). Light CO₂ fixation exhibited two pronounced peaks. In the oxic zone, the highest rates of photosynthesis were detected at 1.0 and 2.0 m. The second, more pronounced peak of light CO₂ fixation was associated with activity of anoxygenic phototrophic bacteria in the anoxic layer at the depth of 2.9 m (413 μg C L^?1 day^?1). Green-colored green sulfur bacteria (GSB) predominated in the upper anoxic layer (2.7–2.9 m), their numbers being as high as 1.12 × 10⁴ cells/mL, while brown-colored GSB predominated in the lower horizons. The rates of both sulfate reduction and methanogenesis peaked in the 2.9 m horizon (1690 μg S L^?1 day^?1 and 2.9 μL CH₄ L^?1 day^-1). The isotopic composition of dissolved methane from the near-bottom water layer (δ¹³C (CH₄) = ?87.76‰) was significantly lighter than in the upper horizons (δ¹³C (CH₄) = ?77.95‰). The most isotopically heavy methane (δ¹³C (CH₄) = ?72.61‰) was retrieved from the depth of 2.9 m. The rate of methane oxidation peaked in the same horizon. As a result of these reactions, organic matter (OM) carbon of the 2.9 m horizon became lighter (?36.36‰), while carbonate carbon became heavier (?7.56‰). Thus, our results demonstrated that Lake Kislo-Sladkoe is a stratified meromictic lake with active microbial cycles of carbon and sulfur. Suspended matter in the water column was mostly of autochthonous origin. Anoxygenic photo-synthesis coupled to utilization of reduced sulfur compounds contributed significantly to OM production.     

Thermophilic Archaeal Diversity and Methanogenesis from El Tatio Geyser Field,Chile

The hydrothermal fluid chemistry at El Tatio Geyser Field (ETGF) in northern Chile suggests that biogenic CO₂–CH₄ cycling may play an important role in water chemistry, and relatively low sulfate (0.6–1 mM) and high molecular hydrogen (H₂) concentrations (67–363 nM) suggest that methanogenic Archaea are present in ETGF microbial mats. In this study, δ¹³C analysis of dissolved inorganic carbon and methane was not indicative of biogenic methane production (δ¹³C_CH4 values ranging from ?15‰ to ?5.3‰); however, methanogenic Archaea were successfully cultured from each of the hydrothermal sites sampled. Sanger sequencing using universal Archaea primers identified putative methanogenic orders with varying metabolic capabilities, including Methanobacteriales, Methanomicrobiales and Methanosarcinales.     

Carbon reservoir perturbations induced by Deccan volcanism: Stable isotope and biomolecular perspectives from shallow marine environment in Eastern India

The Deccan Traps in Western India is hypothesized to have caused significant fluctuations in climatic condition and organic matter (OM) productivity across the Cretaceous-Paleogene Boundary (K/PgB). The periodic release of large amounts of volatiles into the atmosphere is thought to drive these changes. Yet, direct impact of volcanism on the carbon cycle and ecosystem remains relatively unconstrained. For the first time, we attempt to trace changes in both marine and terrestrial carbon reservoirs from pre- and intervolcanic sedimentary units (infra- and inter-trappeans respectively) from Rajahmundry, ~1500 km SE of main eruption sites in Western India. Molecular level characterization of OM and stable isotope composition of carbonates (δ¹³C_carb), bulk OM (δ¹³C_org), and n-alkane (δ¹³C_alk and δD_alk) have been analysed to provide a chemo-stratigraphic framework. In Rajahmundry, high CO₂ concentration estimated from infra-trappean carbonate nodule is synchronous with the onset of the Deccan Traps and the Late Maastrichtian warming episode. Impact of the warming event is reflected in Rajahmundry from a major shift in the terrestrial ecosystem. Marine OM production also seems to have been low throughout the infra-trappean. A steady decrease in δ¹³C_carb values, increase in mortality rates and dwarfism in invertebrates immediately below the first volcanic units in Rajahmundry suggest stressed conditions from eruption in the western part of India ~40–60 kyrs prior to K/PgB. A significant increase in heterotrophic activity is observed after the volcanic deposits in Rajahmundry that seems to have controlled the marine carbon reservoir for a maximum of ~200 kyrs after the boundary. Advent of pteridophytes, increase in carbon content and positive shifts in δ¹³C_carb and δ¹³C_alk values in the upper inter-trappean units mark the onset of recovery in terrestrial and marine environments. Overall, our results suggest significant perturbations in the carbon reservoir as a consequence of the Deccan eruption.     

Stable isotope analysis of modern human hair collected from Asia (China,India, Mongolia,and Pakistan)

We report isotopic data (δ²H, δ¹⁸O n = 196; δ¹³C, δ¹⁵N n = 142; δ³⁴S n = 85) from human hair and drinking water (δ²H, δ¹⁸O n = 67) collected across China, India, Mongolia, and Pakistan. Hair isotope ratios reflected the large environmental isotopic gradients and dietary differences. Geographic information was recorded in H and O and to a lesser extent, S isotopes. H and O data were entered into a recently developed model describing the relationship between the H and O isotope composition of human hair and drinking water in modern USA and pre‐globalized populations. This has anthropological and forensic applications including reconstructing environment and diet in modern and ancient human hair. However, it has not been applied to a modern population outside of the USA, where we expect different diet. Relationships between H and O isotope ratios in drinking water and hair of modern human populations in Asia were different to both modern USA and pre‐globalized populations. However, the Asian dataset was closer to the modern USA than to pre‐globalized populations. Model parameters suggested slightly higher consumption of locally producedfoods in our sampled population than modern USA residents, but lower than pre‐globalized populations. The degree of in vivo amino acid synthesis was comparable to both the modern USA and pre‐globalized populations. C isotope ratios reflected the predominantly C₃‐based regional agriculture and C₄ consumption in northernChina. C, N, and S isotope ratios supported marine food consumption in some coastal locales. N isotope ratios suggested a relatively low consumption of animal‐derived products compared to western populations. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Stable isotope characteristics across narrow savanna/woodland ecotones in Wolfe Creek Meteorite Crater,Western Australia

The stable isotopic composition (δ¹³C) of sediments from lakes are frequently analyzed to reconstruct the proportion of the regional vegetation that used either the C₃ or C₄ photosynthetic pathways, often without conducting a detailed survey of the current local vegetation. We performed a study on the modern vegetation composition within the Wolfe Creek Meteorite Crater to complement our future paleoecological investigation of the crater. A bull’s-eye pattern exists where C₄ grasses dominate an outer ring and salt tolerant species, including shrubs, herbs, chenopods, and halophytic algae, dominate the inner pan of the crater. The ecotone between the inner and outer zones is narrow and occupied by tall (>7 m) Acacia ampliceps, with some C₄ grasses in the understory. Along with the highest water table and most saline soils the center of the crater has C₃ plants present with the highest δ¹³C and δ¹⁵N values. The range of δ¹³C and δ¹⁵N values from the analysis of surface soil organic matter (OM) was much smaller compared with the range of values from plant materials implying that either: (1) the current plant OM has not yet been integrated into the soils, or (2) processes within the soil have acted to homogenize isotopic variability within the crater. The application of a two end member mixing model to calculate %C₄ and %C₃ biomass from the δ¹³C of surface soil OM was complicated by: (1) the crater containing both a dry habitat with C₄ grasses and a central pan with C₄ halophytic plants and, (2) the large variation in the δ¹³C of the plants and soil OM.     

The effect of various iron hydroxide concentrations on the anaerobic fermentation of sulfate-containing model wastewater

The addition of iron hydroxide and iron-reducing bacteria into a reactor for anaerobic processing of sulfate-containing wastewater was shown to decrease sulfate reduction and sulfide concentration, while increasing the total organic carbon (TOC) and methane production. The effect of iron (III) in sulfate-containing wastewater depended on its dose, which can be expressed as molar ratio Fe(III)/SO ₄ ^2? . Sulfide concentration increased monotonically, reaching 91 and 45 mg/l after 15 days of processing at Fe(III)/SO ₄ ^2? ratios of 0.06 and 0.5, respectively. However, soluble sulfide production was not observed at ratios equaling 1 and 2. At ratios of 0.06, 0.5, 1, and 2, the maximum rates of TOC removal were 0.75, 1.15, 1.39, and 1.55 g TOC/g of organic matter (OM) per 1 h. Methane production rates were 0.039, 0.047, 0.064, and 0.069 ml/g OM per 1 h, with the mean relative amounts of methane in the biogas being equal to 25, 41, 55, and 62%, respectively. These data can be applied to the development of new methods of anaerobic purification of sulfate-containing wastewater.     

Controls on the origin and cycling of riverine dissolved inorganic carbon in the Brazos River, Texas

Rivers draining watersheds that include carbonate bedrock or organic matter (OM)-rich sedimentary rocks frequently have ¹⁴C-depleted dissolved inorganic carbon (DIC) relative to rivers draining carbonate- and OM-free watersheds, due to dissolution of carbonate and/or decomposition of ancient OM. However, our results from a subtropical river, the Brazos River in Texas, USA, show that in this watershed human activities appear to dominate basin lithology in controlling the origin and metabolism of DIC. The middle Brazos flows through limestone and coal-bearing bedrock, but DIC isotope data suggest no limestone dissolution or respiration of ancient OM, and instead reflect efficient air?Cwater CO₂ exchange, degradation of relatively young OM and photosynthesis in the river as a result of river damming and urban treated wastewater input. The lower Brazos drains only small areas of carbonate and coal-bearing bedrock, but DIC isotope data suggest the strong influence of carbonate dissolution, with a potentially minor contribution from decomposition of old soil organic matter (SOM). Oyster shells and crushed carbonate minerals used in road construction are likely sources of carbonate in the lower Brazos, in addition to natural marl and pedogenic carbonate. Additionally, the generally low pCO₂ and high DIC concentration in the Brazos River lead to a low CO₂ outgassing:DIC export ratio, distinguishing the Brazos River from other rivers.     

Carbonate facies‐specific stable isotope data record climate,hydrology, and microbial communities in Great Salt Lake,UT

Organic and inorganic stable isotopes of lacustrine carbonate sediments are commonly used in reconstructions of ancient terrestrial ecosystems and environments. Microbial activity and local hydrological inputs can alter porewater chemistry (e.g., pH, alkalinity) and isotopic composition (e.g., δ¹⁸O_water, δ¹³C_DIC), which in turn has the potential to impact the stable isotopic compositions recorded and preserved in lithified carbonate. The fingerprint these syngenetic processes have on lacustrine carbonate facies is yet unknown, however, and thus, reconstructions based on stable isotopes may misinterpret diagenetic records as broader climate signals. Here, we characterize geochemical and stable isotopic variability of carbonate minerals, organic matter, and water within one modern lake that has known microbial influences (e.g., microbial mats and microbialite carbonate) and combine these data with the context provided by 16S rRNA amplicon sequencing community profiles. Specifically, we measure oxygen, carbon, and clumped isotopic compositions of carbonate sediments (δ¹⁸O_carb, δ¹³C_carb, ?₄₇), as well as carbon isotopic compositions of bulk organic matter (δ¹³C_org) and dissolved inorganic carbon (DIC; δ¹³C_DIC) of lake and porewater in Great Salt Lake, Utah from five sites and three seasons. We find that facies equivalent to ooid grainstones provide time‐averaged records of lake chemistry that reflect minimal alteration by microbial activity, whereas microbialite, intraclasts, and carbonate mud show greater alteration by local microbial influence and hydrology. Further, we find at least one occurrence of ?₄₇ isotopic disequilibrium likely driven by local microbial metabolism during authigenic carbonate precipitation. The remainder of the carbonate materials (primarily ooids, grain coatings, mud, and intraclasts) yield clumped isotope temperatures (T(?₄₇)), δ¹⁸O_carb, and calculated δ¹⁸O_water in isotopic equilibrium with ambient water and temperature at the time and site of carbonate precipitation. Our findings suggest that it is possible and necessary to leverage diverse carbonate facies across one sedimentary horizon to reconstruct regional hydroclimate and evaporation–precipitation balance, as well as identify microbially mediated carbonate formation.     

Metabolic threshold and sulfide-buffering in diffusion controlled marine sediments impacted by continuous organic enrichment

The effects of organic enrichment on sediment biogeochemistry was studied in diffusion controlled sediment mesocosms, where labile organic matter (OM) (fish feed) pulses were added once a week to the sediment surface. Two types of sediments, differing mainly in content of reactive Fe, were used. The aim of this experiment was two-fold, (1) to evaluate the importance of Fe-driven sulfide buffering for sulfide accumulation in surface enriched sediments, and (2) to estimate the diagenetic capacity for degradation of labile OM near the sediment surface. The simulated OM loading rate of 375 mmol C m^?2 day^?1 led to a 5–6 times increase in CO₂-production and a 4–5 times increase in O₂-uptake. Sulfate reduction estimated by radiotracer experiments and CO₂-release was 105–131 mmol m^?2 day^?1, but accumulation of porewater sulfide was low in both sediment types. Instead 99% of sulfide was oxidized with O₂ at the sediment water interface in the low Fe treatment, whereas 46% of produced sulfide precipitated as Fe-S compound in the high Fe treatment resulting in significantly lower O₂-uptake. Furthermore, the accumulation of up to 30% of added OM by the end of the experiment indicated a saturation of the heterotrophic microbial communities in the upper enriched surface layer. These results suggest a maximum diagenetic capacity for OM degradation in the range of ~25 μmol C cm^?3 day^?1 or 260 mmol m^?2 day^?1 for the present sediment types.     

Chemical speciation of oxalato complexes of indium(III)

Abstract

Chemical speciation of binary complexes of indium(III) with oxalic acid has been investigated pH metrically at 303 K and at an ionic strength of 0.2 mol dm^?3. The approximate formation constants have been calculated with the computer program SCPHD utilizing the experimental data obtained by monitoring H⁺ ion concentration. The formation constants thus obtained are refined with the computer program, MINIQUAD75 using primary alkalimetric data. The selection of the best-fit chemical model is based on the statistical parameters and residual analysis. The major complexes formed are In(C₂O₄)₂^?, In(C₂O₄)₃^3?, [In(C₂O₄)₂OH]^2? and [In(C₂O₄)₂ (OH)₂]^3?. The distribution patterns of the different species with the pH values showed that In(C₂O₄)₂^? is the predominant species.     

Paleoecology of Neoproterozoic hypersaline environments: Biomarker evidence for haloarchaea,methanogens, and cyanobacteria

While numerous studies have examined modern hypersaline ecosystems, their equivalents in the geologic past, particularly in the Precambrian, are poorly understood. In this study, biomarkers from ~820 million year (Ma)‐old evaporites from the Gillen Formation of the mid‐Neoproterozoic Bitter Springs Group, central Australia, are investigated to elucidate the antiquity and paleoecology of halophiles. The sediments were composed of alternating laminae of dolomitized microbial mats and up to 90% anhydrite. Solvent extraction of these samples yielded thermally well‐preserved hydrocarbon biomarkers. The regularly branched C₂₅ isoprenoid 2,6,10,14,18‐pentamethylicosane, the tail‐to‐tail linked C₃₀ isoprenoid squalane, and breakdown products of the head‐to‐head linked C₄₀ isoprenoid biphytane, were particularly abundant in the most anhydrite‐rich sediments and mark the oldest current evidence for halophilic archaea. Linear correlations between isoprenoid concentrations (normalized to n‐alkanes) and the anhydrite/dolomite ratio reveal microbial consortia that fluctuated with changing salinity levels. Halophilic archaea were the dominant organisms during periods of high salinity and gypsum precipitation, while bacteria were prevalent during stages of carbonate formation. The irregularly branched C₂₅ isoprenoid 2,6,10,15,19‐pentamethylicosane (PMI), with a central tail‐to‐tail link, was also abundant during periods of elevated salinity, highlighting the activity of methanogens. By contrast, the irregularly branched C₂₀ isoprenoid 2,6,11,15‐tetramethylhexadecane (crocetane) was more common in dolomite‐rich facies, revealing that an alternate group of archaea was active during less saline periods. Elevated concentrations of isotopically depleted heptadecane (n‐C₁₇) revealed the presence of cyanobacteria under all salinity regimes. The combination of biomarkers in the mid‐Neoproterozoic Gillen Formation resembles lipid compositions from modern hypersaline cyanobacterial mats, pointing to a community composition that remained broadly constant since at least the Neoproterozoic. However, as a major contrast to most modern hypersaline environments, the Gillen evaporites did not yield any evidence for algae or other eukaryotes.     

Kairomonal effect of some saturated hydrocarbons on the egg parasitoids, Trichogramma brasiliensis (Ashmead) and Trichogramma exiguum, Pinto, Platner and Oatman (Hym., Trichogrammatidae)

Abstract: Bioassay studies carried out on the egg parasitoids Trichogramma brasiliensis and T. exiguum with 11 straight chain‐saturated hydrocarbons, revealed that pentacosane and hexacosane recorded very high parasitoid activity index (PAI) and parasitism for both the parasitoids indicating high kairomonal activity. These were followed by docosane, tricosane, heneicosane, hexatriacontane and tetracosane, which may be grouped as favourable hydrocarbons showing varying levels of kairomonal activity for T. brasiliensis, as compared to eicosane, pentadecane, octacosane and heptadecane, which can be grouped as non‐favourable hydrocarbons. In the case of T. exiguum, pentacosane‐treated egg cards showed maximum parasitism followed by hexacosane, pentadecane, hexatriacontane, tricosane and docosane thereby indicating their kairomonal activity in comparison with heptadecane, tetracosane, eicosane, heneiocosane and octacosane which recorded low levels of parasitism. In the case of T. brasiliesnsis, tetracosane recorded the highest response at the lowest concentration, C₁ (62.5 ng/cm²), which decreased as the concentration increased. Eicosane, heneicosane and docosane recorded the highest parasitism at C₂ (125 ng/cm²). In heptadecane, tricosane, pentacosane and hexatriacontane the highest parasitism was recorded at the medium concentration, C₃ (250 ng/cm²). Octacosane recorded the highest response at C₄ (375 ng/cm²). Pentadecane and hexacosane‐treated egg cards showed their highest response at C₅ (500 ng/cm²). In the case of T. exiguum, the lowest concentration, C₁ evoked the highest response in hexacosane, whereas heptacosane, heneiocosane, docosane and tetracosane recorded the highest parasitism at C₂. Eicosane, pentacosane and octacosane recorded maximum parasitism, at C₃, whereas tricosane and hexatriacontane showed maximum parasitism at C₄ and pentadecane at C₅. These concentrations can be taken as the optimum concentration to increase parasitization by these parasitoids. The favourable hydrocarbons at their optimum concentration can be used for efficient management of these parasitoids in field releases.     

A molecular marker-based assessment of sedimentary organic matter sources and distributions in Florida Bay

Seven surface sediment samples covering the general geographical area of Florida Bay were examined through the measurement of ¹³C isotopic abundance and lipid classes to assess the distributions and sources of organic matter (OM) in this estuarine environment. The bulk δ¹³C_org value shifted from a more isotopically depleted (−19.9‰) to a more isotopically enriched (−13.5‰) signal along the NE to SW transect. Two geochemical proxies (Paq and C₂₅/C₂₇ n-alkan–2-ones) indicative of seagrass-derived OM significantly increased from near-shore to offshore areas, while taraxerol, a biomarker for mangroves, substantially decreased from 7200 to 284 ng/g along that transect. A clear spatial variation of OM sources was observed in Florida Bay. Generally, the sites in the NE contained mixed OM sources of terrestrial (mangrove) and seagrass-derived OM, where the terrestrial component accounted for over 60% of the OM. In contrast, the sites in central and SW Florida Bay were strongly dominated by seagrass-derived OM. Other lipid fractions such as fatty acids, n-alcohols and sterols revealed an important contribution of algae and bacteria especially in the central and SW section of the Bay. Relatively abundant C₂₅ HBIs suggest important marine diatom inputs, while the presence of C₂₀ HBIs particularly in central Florida Bay possibly reflects the contribution of cyanobacterial mats. The molecular proxies developed in this study to assess OM sources in Florida Bay are promising tools for the characterization and seasonal variability assessment of OM in this and other similar subtropical and tropical estuaries and for paleoenvironmental studies. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Dark CO2 fixation into phospholipid-derived fatty acids by the cold-water coral associated sponge Hymedesmia (Stylopus) coriacea (Tisler Reef,NE Skagerrak)

ABSTRACT

Many cold-water sponges harbour microorganisms of which the role in the sponge host remains enigmatic. Here, we show a transfer of fixed inorganic carbon by sponge-associated microbes to its host, the cold-water coral encrusting sponge Hymedesmia (Stylopus) coriacea. Sponge were collected at approx. 100?m depth and incubated for 1.5–2.5 days with ¹³C labelled dissolved inorganic carbon (DIC) as tracer. Total DIC fixation rates ranged from 0.03–0.11?mmol C?×?mmol C_sponge × d^?1. ¹³C-tracer was recovered in bacterial-specific (i.e. short and branched) and sponge-specific (very long-chained) phospholipid-derived fatty acids (PLFA's), but was not incorporated into archaeal lipids. ¹³C-incorporation in biomarkers such as C16:1w7c and C18:1w7c indicated that nitrifying and/or sulphur-oxidizing bacteria (chemoautotrophs) were likely active in the sponge. Trophic transfer of microbially-fixed carbon to the sponge host was confirmed by recovery of label in very long chain fatty acids (VLCFA's) including C26:2 and C26:3. Tracer accumulation into several VLCFA's continued after removal of ¹³C-DIC, while tracer in most bacteria-specific PLFA's declined, indicating a transfer and elongation of bacterial-specific PLFA's to sponge-specific PLFA's. This implies that PLFA precursors released from chemo- as well as heterotrophic microbes in sponges contributed to the synthesis of VLCFA's, identifying sponge-associated bacteria as symbionts of the sponge.