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Recently developed temperature proxies based on hydroxylated isoprenoid Glycerol Dialkyl Glycerol Tetraethers (OH-isoGDGTs), such as % O H , R I - O H , R I - O H ′ and O H C , have shown potential for reconstructing past temperature changes. However, progress has been limited by the lack of a global core-top calibration with ample geographical coverage. Here, we compile an extensive global surface sediment dataset of OH-isoGDGTs as well as regular isoprenoid GDGTs (isoGDGTs), with both data generated at NIOZ (n = 575) and previously published data from other laboratories (n = 297). We find interlaboratory differences for proxy indices that incorporate both OH-isoGDGTs and regular isoGDGTs, indicating that care must be taken in compiling large GDGT datasets from multiple laboratories. Our results confirm a strong temperature signal in the isoGDGT distribution, especially for OH-isoGDGT-0 and non-hydroxylated isoGDGTs, but also reveal that water depth might have an impact on the distribution of OH-isoGDGTs with 1 and 2 cyclopentane moieties. This will affect the R I - O H and R I - O H ′ indices, particularly in tropical regions, where OH-isoGDGT-0 occurs at low abundance. We explore new proxy indices that combine the temperature dependence of both isoGDGT and OH-isoGDGT distributions and propose the use of T E X 86 O H , which includes OH-isoGDGT-0 in the denominator of the T E X 86 index. This modification leads to a much higher temperature sensitivity of the index, especially in regions with annual mean sea surface temperatures between 5 and 15 °C. Application of this novel paleothermometer to a polar sediment core suggests that this proxy is likely to result in more reliable temperature reconstructions in polar regions where OH-isoGDGTs are abundant. [ABSTRACT FROM AUTHOR]

The marine pelagic archaeal community is dominated by three major groups, the marine group I (MGI) Thaumarchaeota, and the marine groups II and III (MGII and MGIII) Euryarchaeota. Studies of both MGI cultures and the environment have shown that the MGI core membrane lipids are predominantly composed of glycerol dibiphytanyl glycerol tetraether (GDGT) lipids and the diether lipid archaeol. However, there are no cultured representatives of MGII and III archaea and, therefore, both their membrane lipid composition and potential contribution to the marine archaeal lipid pool remain unknown. Here, we show that GDGTs present in suspended particulate matter of the (sub)surface waters of the North Atlantic Ocean and the coastal North Sea are derived from MGI archaea, and that MGII archaea do not significantly contribute to the pool of GDGTs and archaeol. This implies, in contrast to previous suggestions, that their lipids do not affect the widely used sea surface temperature proxy TEX86. These findings also indicate that MGII archaea are not able to produce any known archaeal lipids, implying that our understanding of the evolution of membrane lipid biosynthesis in Archaea is far from complete. [ABSTRACT FROM AUTHOR]

• High diversity of the archaeal community in the Mediterranean Sea water column. • Dominance of Euryarchaeota Group II and III in upper epipelagic waters (0–100 mbsl). • Shift in archaeal community composition coincided with a change in IPL distribution. • Ratio of GDGT-2/GDGT-3 increased with water depth. • Thaumarchaeota were abundant in the deeper part of the water column. Thaumarchaeota are one of the most abundant groups of Archaea in the marine water column. Their membrane consists of isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) which are applied in the widely used TEX 86 proxy to reconstruct past sea surface temperatures (SSTs). However, in some specific marine systems, such as the Mediterranean Sea, core-top TEX 86 -derived temperatures do not seem to reflect annual mean SSTs. This has been attributed to contributions of deep-water dwelling Thaumarchaeota. Here, we investigate the potential causes of this bias by studying both the archaeal diversity as well as the intact polar lipid (IPL) GDGT composition in the Mediterranean water column by a combined 16S rRNA gene amplicon sequencing and a lipidomic approach on suspended particulate matter (SPM) at different water depths. The archaeal distribution showed a dominance of archaea other than Thaumarchaeota, i.e. Marine Euryarchaeota group II and III in the upper epipelagic waters (0–100 m deep), while Thaumarchaeota (Marine group I; MGI) dominated the subsurface and the deeper waters. This shift in the archaeal community composition coincided with a decrease in IPL GDGT-0 and increase of IPL crenarchaeol. The ratio of GDGT-2/GDGT-3 increased with water depth, but values were lower than observed in deep marine waters of some other regions. The increase of the GDGT-2/GDGT-3 ratio coincided with the high relative abundance of deep-water MGI, which may be linked to the high temperature and salinity found in specific water masses of the Mediterranean Sea. We conclude that these particularities of the Mediterranean Sea are responsible for the overestimated SST based on TEX 86. [ABSTRACT FROM AUTHOR]

Glycerol monoalkyl glycerol tetraethers (GMGTs) are a group of membrane spanning lipids produced by some species of archaea and bacteria. They differ from the more commonly studied glycerol dialkyl glycerol tetraethers (GDGTs) in having an additional covalent carbon-carbon bond connecting the two alkyl chain. The relative abundance and distribution of bacterial branched GMGTs (brGMGTs) in surface sediments from a set of East African lakes were studied. The abundance of brGMGTs relative to the brGDGTs is positively correlated to measured mean annual air temperature (MAAT), although with a significant amount of scatter. BrGMGT abundance was not correlated to lake water pH. Seven major brGMGTs that vary in degree of methylation were identified, with m / z 1020, 1034 and 1048. Further, the mass chromatograms of the m / z 1020 and 1034 brGMGTs show an interesting distribution of peaks, which likely relates to the occurrence of distinct brGMGT isomers. This structural complexity is higher than previously observed in peats and marine sediments. Principal component analysis of the fractional abundance of bacterial tetraether lipids revealed the brGMGTs behave similarly to one another but differently from both the 5- or 6-methyl brGDGTs. This suggests the brGMGTs are produced by a common source organism and are methylated at a different position. The distribution of the seven brGMGTs showed considerable correlation with MAAT. This variability was captured in a new proxy index (the brGMGTI), which showed a strong positive linear relationship with MAAT. Lacustrine brGMGTs show potential to be applied to ancient settings to provide information about paleoclimate. [ABSTRACT FROM AUTHOR]

Understanding how microbial lipidomes adapt to environmental and nutrient stress is crucial for comprehending microbial survival and functionality. Certain anaerobic bacteria can synthesize glycerolipids with ether/ester bonds, yet the complexities of their lipidome remodeling under varying physicochemical and nutritional conditions remain largely unexplored. In this study, we thoroughly examined the lipidome adaptations of Desulfatibacillum alkenivorans strain PF2803T, a mesophilic anaerobic sulfate-reducing bacterium known for its high proportions of alkylglycerol ether lipids in its membrane, under various cultivation conditions including temperature, pH, salinity, and ammonium and phosphorous concentrations. Employing an extensive analytical and computational lipidomic methodology, we identified an assemblage of nearly 400 distinct lipids, including a range of glycerol ether/ester lipids with various polar head groups. Information theory-based analysis revealed that temperature fluctuations and phosphate scarcity profoundly influenced the lipidome's composition, leading to an enhanced diversity and specificity of novel lipids. Notably, phosphorous limitation led to the biosynthesis of novel glucuronosylglycerols and sulfur-containing aminolipids, termed butyramide cysteine glycerols, featuring various ether/ester bonds. This suggests a novel adaptive strategy for anaerobic heterotrophs to thrive under phosphorus-depleted conditions, characterized by a diverse array of nitrogen-and sulfur-containing polar head groups, moving beyond a reliance on conventional nonphospholipid types. [ABSTRACT FROM AUTHOR]

Previous studies have shown that heterocyst glycolipids (HGs) are unique markers for N 2 -fixing heterocystous cyanobacteria. In this study, the HGs of a marine pelagic Calothrix sp. CCY1611 isolated from the tropical western North Atlantic were analyzed by ultra-high pressure liquid chromatography–high resolution mass spectrometry and it was shown that this organism contains an unusual C 28 triol HG with a methylated C 6 sugar (methyl-HG 28 triol) head group. Gas chromatography–mass spectrometry analysis of the sugar released from the novel HG by acid methanolysis revealed that the sugar is likely 6-O-methyl-β- d -glucopyranose. We propose that this methyl-HG 28 triol is a potential biomarker for pelagic members of the genus Calothrix . [ABSTRACT FROM AUTHOR]

Thaumarchaeota synthesize specific glycerol dibiphytanyl glycerol tetraethers (GDGTs), the distribution of which is affected by temperature, thereby forming the basis of the paleotemperature proxy, TEX 86 . Lipids in marine surface sediments are believed to be derived mainly from pelagic Thaumarchaeota; however, some studies have evaluated the possibility that benthic Archaea also contribute to the lipid fossil record. Here, we compared the archaeal abundance and composition from DNA-based methods with the archaeal intact polar lipid (IPL) diversity in surface sediments of a seasonally hypoxic marine lake to determine the potential biological sources of the sedimentary archaeal IPLs under changing environmental conditions. The archaeal community changed from March (oxic conditions) to August (euxinic) from a Thaumarchaeota-dominated community (up to 82%) to an archaeal community dominated by the DPANN super phylum (up to 95%). This marked change coincided with a one order of magnitude decrease in the total IPL-GDGT abundance. In addition, IPL-GDGTs with a glyco polar head group increased. This may indicate a transition to Thaumarchaeota growing in stationary phase or selective preservation of the GDGT pool. In addition, considering the apparent inability of the DPANN Archaea to synthesize their own membrane lipids, we hypothesize that the dominant DPANN Archaea population present in August use the lipids synthesized previously by the Thaumarchaeota or other Archaea to form their own cell membranes, which would indicate an active recycling of fossil IPLs in the marine surface sediment. [ABSTRACT FROM AUTHOR]

The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils, peats, and lake sediments has been shown to correlate with mean annual air temperature (MAAT) and has provided valuable new climate reconstructions. Here we use an improved chromatographic method to quantify the fractional abundances of 5- and 6-methyl isomers in surface sediments from 65 East African lakes spanning temperatures 1.6–26.8 °C, and investigate the relationships between these fractional abundances and temperature, lake pH, and other environmental variables. We find that temperature exerts a strong control on brGDGT distributions, including the relative abundances of 5- and 6-methyl isomers, whereas other environmental variables, including lake pH, are weakly correlated to the fractional abundances of the brGDGTs. The distributions of brGDGTs in our lake sediments differ from those of soils and peats, leading to temperature offsets if soil- and peat-based brGDGT temperature calibrations are applied. We develop new calibrations for MAAT for use in lake sediment based upon the MBT′5Me and Index 1 ratios, as well as a multivariate regression of brGDGT fractional abundances on temperature using stepwise forward selection. We obtain root mean square errors (RMSE) between ∼ 2.1 and 2.5 °C for these calibrations, highlighting the potential for brGDGTs to provide precise temperature reconstructions using lake sediment cores. Calibrations for lake pH perform more poorly, likely due to weak correlations between pH and brGDGT distributions in East African lakes. These results indicate that quantification of 5- and 6-methyl isomers separately in lake sediment can improve paleoclimatic reconstructions. [ABSTRACT FROM AUTHOR]

We have compared and assessed the suitability of several chromatographic methods for the analysis of long chain alkenones and long chain diols and the associated paleotemperature proxies (U K’ 37 and LDI). We evaluated the traditional methods for the analysis of the U K’ 37 and the LDI, gas chromatography (GC) − flame ionization detection (FID) and GC mass spectrometry (MS) using selected ion monitoring (SIM), respectively, and developed a new method using GC–MS/MS in multiple reaction monitoring mode (MRM) for the analysis of long chain diols as well as a method for automatic silylation of diols using a robot autosampler. Finally, we evaluated liquid chromatography (LC) methods to simultaneously measure the U K’ 37 and the LDI, using ultra high performance LC (UHPLC) with low (nominal mass) resolution MS in SIM mode, and UHPLC with high resolution MS (HRMS). Detection and quantification limits and reproducibility were assessed by means of serial dilutions of culture extracts. Automated silylation by a robot autosampler showed similar reproducibility as off-line silylation while substantially decreasing sample preparation time. The novel MRM method had a slightly lower limit of quantification (LOQ; i.e. 0.3 pg C 28 1,13-diol injected on-column) than the traditional method (0.5 pg) and improved reproducibility while allowing more unambiguous identification of LCDs in complex matrices. For diols, UHPLC–MS using SIM had the highest LOQ (i.e. 15 pg) and a comparable reproducibility as GC–MS. UHPLC–HRMS had a LOQ of ca. 1.5 pg, and an improved reproducibility for diol analysis. For alkenone analysis, both UHPLC–HRMS and UHPLC–MS using SIM were 2–3 orders of magnitude more sensitive (LOQ ca. 20 and 2 pg C 37:2 alkenone injected on-column, respectively) than GC-FID (LOD ca. 3 ng), with a similar reproducibility of the U K’ 37 index. Hence, UHPLC–HRMS allows simultaneous analysis of the U K’ 37 and LDI at an increased sensitivity. In addition, it allows simultaneous measurement of TEX 86 , a temperature proxy based on the isoprenoid glycerol dialkyl glycerol tetraethers. This reduces the preparation time by excluding the need of derivatization and separation of the ketone (containing the long chain alkenones) and polar fractions (containing the long chain diols and GDGTs). However, synthetic standards are required to fully assess the accuracy of the new methods for determination of the LDI and U K’ 37 . [ABSTRACT FROM AUTHOR]

• S-GDGTs and novel S-GDDs (with a cyclohexane ring) determined in lacustrine sediments. • Their distribution is related to anoxic conditions in bottom waters. • GMGTs and GMDs detected in Messel oil shale indicate non-thermophilic archaea. We examined membrane-spanning archaeal lipids using ultra high pressure liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) in a suite of sediment samples from both cored sequences (Messel oil shale and Lake Chala) and surface sediments (Azorean lakes) encompassing ancient and modern (Eocene to Present) lacustrine environments. Additionally we compared the lacustrine data to those of marine (Mediterranean cored sequences, Arabian Sea surface sediments and Monterey outcrop sediments) and hypersaline sediments (Vena del Gesso marls) as well as marine suspended particulate matter (SPM) from the Black Sea. Regular isoprenoidal glycerol dialkyl glycerol tetraethers (GDGTs) and glycerol dialkyl diethers (GDDs) were the most abundant membrane-spanning lipids in all investigated settings (>90 % and 84 % respectively). Interestingly, GDGTs with a cyclohexyl ring (S-GDGTs) were also present in almost all investigated lake sediments, in relative abundances of ca. 2–7 % and, for the first time, also their S-GDD counterparts were detected (2–10 %). The producers of S-GDGTs are still unknown, however our results show that it is likely that bottom water anoxia (both seasonally induced or permanent) is the driving factor for the production of these lipids, whereas previous studies suggested euxinia was required for production. Unsaturated GDGTs (uns -GDGTs, ca. 2 %) were only detected in Lake Chala sediments and surface sediments from Azorean lakes, but without accompanying uns -GDDs. GMGTs, glycerol monoalkyl glycerol tetraethers, were present in Messel oil shale and marine samples, while GMDs were only found in Messel oil shale. [ABSTRACT FROM AUTHOR]

We characterized the intact polar lipid (IPL) composition in the surface waters of 22 lakes from Minnesota and Iowa, ranging in trophic state between eutrophic and oligo-mesotrophic, to investigate the impact of trophic state on IPL composition. A high diversity of IPL classes was detected. Most IPL classes were detected in all lakes, but the eutrophic lakes contained a significantly higher relative abundance of lyso-phosphatidylcholine (PC) than the oligo-mesotrophic lakes, which in turn were characterized by significantly higher relative abundance of hydroxymethyltrimethyl-alanine/trimethyl-homoserine (DGTA/DGTS) betaines, ornithine lipids and the recently discovered trimethyl ornithine (TMO) lipids. The higher relative abundance of ornithines and TMOs may relate to a higher contribution of heterotrophic bacteria relative to phytoplankton while the higher abundance of the DGTA/DGTS betaines may relate to substitution by microorganisms of these non-P lipids for PC under P-stress, as has been observed in other environments. We also detected a variety of heterocyst glycolipids (HGs) derived from N2-fixing heterocystous Cyanobacteria in all lakes, suggesting the presence of these Cyanobacteria in the full range of trophic conditions. Correlation of HG abundance with environmental data showed that high productivity lakes have high HG abundances, while other distributional differences in HGs, which did not correlate with environmental parameters, are likely due to differences in species composition. We conclude that the significant differences in IPL composition between the eutrophic and oligo-mesotrophic lakes are either due to adaptation of the membrane composition to nutrient conditions or due to general divergences in microbial composition under the different conditions. [ABSTRACT FROM AUTHOR]

RATIONALE: Intact polar lipids (IPLs) are the building blocks of cell membranes, and amino acid containing IPLs have been observed to be involved in response to changing environmental conditions in various species of bacteria. Highperformance liquid chromatography/mass spectrometry (HPLC/MS) has become the primary method for analysis of IPLs. Many glycerol-free amino acid containing membrane lipids (AA-IPLs), which are structurally different than abundant aminophospholipids, have not been characterized using HPLC/MS. This results in many lipids remaining unrecognized in IPL analysis of microbial cultures and environmental samples, hampering the study of their occurrence and functionality. METHODS: We analyzed the amino acid containing IPLs of a number of bacteria (i.e. Gluconobacter cerinus, Cyclobacterium marinus, Rhodobacter sphaeroides, and Pedobacter heparinus) in order to decipher fragmentation pathways, and explore potential novel lipid structures using HPLC/electrospray ionization ion trap MS (HPLC/ESI-IT-MS) and HPLC/high-resolution MS (HPLC/HRMS). RESULTS: We report differentiation between glutamine and lysine lipids with the same nominal masses, novel MS fragmentation pathways of cytolipin, the lipopeptides cerilipin and flavolipin, head group hydroxylated ornithine lipids, and the novel identification of cerilipin with a hydroxylated fatty acid. CONCLUSIONS: Non-glycerol AA lipids can be readily recognized as their fragmentation follows a clear pattern with initial dehydration or other loss from the head group, followed by fatty acid losses resulting in a diagnostic fragment ion. Higher level MSn and HRMS are valuable tools in characterizing AA lipid head group structural components. [ABSTRACT FROM AUTHOR]

The development of methods using liquid chromatography coupled to mass spectrometry to analyze glycerol dialkyl glycerol tetraethers (GDGTs) has substantially expanded the biomarker tool box and led to the development of several new proxies. Recent studies have shown that new high performance liquid chromatography methods have substantially improved separation of GDGT isomers and detection of novel isomers. Here we present a chromatographic method based on two ultra-high performance liquid chromatography silica columns capable of separating a wide range of GDGTs with good resolution and which compares favorably with previously published methods. This method was tested on a part of the global calibration set of the TEX 86 , a proxy for sea water temperature, and on a part of the global calibration set of the MBT 5Me , a proxy for air temperature, and CBT′, a proxy for soil pH. Our results show that the new high resolution chromatography method leads to a significant but small offset (< 0.01 or < 0.8 °C) in TEX 86 , especially at low values, while no difference is observed for the CBT′. However, for the MBT 5Me a significant difference is observed (< 0.01 or < 3 °C), especially at low values, although this difference is smaller than the calibration error (4.8 °C). [ABSTRACT FROM AUTHOR]

Marine endosymbiotic heterocystous cyanobacteria make unique heterocyst glycolipids (HGs) containing pentose (C 5 ) moieties. Functionally similar HGs with hexose (C 6 ) moieties found in free-living cyanobacteria occur in the sedimentary record, but C 5 HGs have not been documented in the natural environment. Here we developed a high performance liquid chromatography multiple reaction monitoring (MRM) mass spectrometry (HPLC–MS 2 ) method specific for trace analysis of long chain C 5 HGs and applied it to cultures of Rhizosolenia clevei Ostenfeld and its symbiont Richelia intracellularis which were found to contain C 5 HGs and no C 6 HGs. The method was then applied to suspended particulate matter (SPM) and surface sediment from the Amazon plume region known to harbor marine diatoms carrying heterocystous cyanobacteria as endosymbionts. C 5 HGs were detected in both marine SPM and surface sediments, but not in SPM or surface sediment from freshwater settings in the Amazon basin. Rather, the latter contained C 6 HGs, established biomarkers for free-living heterocystous cyanobacteria. Our results indicate that the C 5 HGs may be potential biomarkers for marine endosymbiotic heterocystous cyanobacteria. [ABSTRACT FROM AUTHOR]

The TEX 86 is a widely used paleotemperature proxy based on isoprenoid glycerol dibiphytanyl glycerol tetraethers (GDGTs) produced by Thaumarchaeota. Archaeal membranes are composed of GDGTs with polar head groups (IPL-GDGTs), most of which are expected to be degraded completely or transformed into more recalcitrant core lipid (CL)-GDGTs upon cell lysis. Here, we examined the differences in concentration and distribution of core lipid (CL)- and intact polar lipid (IPL)-GDGTs in surface sediments at different deposition depths, and different oxygen bottom water concentrations (<3–83 μmol L −1 ). Surface sediments were sampled from 900 to 3000 m depth on a seamount (Murray Ridge), whose summit protrudes into the oxygen minimum zone of the Arabian Sea. Concentrations of organic carbon, IPL- and CL-GDGTs decreased linearly with increasing maximum residence time in the oxic zone of the sediment ( t OZ ), suggesting increasing sedimentary degradation of organic matter and GDGTs. IPL-GDGT-0 was the only exception and increased with t OZ , indicating that this GDGT was probably produced in situ in the surface sediment. Concentrations of crenarchaeol with glycosidic headgroups decreased with increasing t OZ , while crenarchaeol with a hexose, phosphohexose head (HPH) group, in contrast, showed an increase with increasing t OZ , indicating that the concentration of HPH crenarchaeol was primarily determined by in situ production in surficial sediments. TEX 86 values of both IPL-derived GDGTs and CL-GDGTs decreased by ∼0.08 units with increasing water depth, in spite of the sea surface temperatures being identical for the restricted area studied. In situ production in sediments could be excluded as the main cause, due to the slow production rates of GDGTs in sediments, and previous observations of the same trends in TEX 86 in sediment trap material. Instead, the incorporation of GDGTs produced in the oxygen minimum zone (with high TEX 86 values) and their preferential degradation during the sinking through the water column, or differential degradation of IPL-GDGTs per head group could be the causes for the observed change in TEX 86 values. The effect of differential degradation might cause differences between oxic and anoxically deposited sediments, and, together with a potential deep water contribution on TEX 86 values, could translate into changes in reconstructed temperature of <3 °C, which might have to be accounted for in TEX 86 calibration and paleotemperature studies of deep water sedimentary records. [ABSTRACT FROM AUTHOR]

The distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils has been shown to correlate with the soil pH and the mean annual air temperature (MAT). This has been used to perform palaeoclimate reconstructions based on brGDGTs recovered from palaeosoils, freshwater, and marine sedimentary archives. Recently described 6-methyl brGDGTs were shown to co-elute with the 5-methyl brGDGTs that are used to calculate the CBT and MBT′ indices used as palaeoclimate proxies. The impact of these 6-methyl brGDGTs on the established palaeoclimate proxies is unknown and will depend on their abundance in soils. Using improved chromatography, we quantified the fractional abundance of 6-methyl brGDGTs in globally distributed soils and show that they are abundant components, comprising on average 24% of the total amount of brGDGTs. All penta- and hexa-methylated brGDGTs (i.e. with zero to two cyclopentane moieties) were shown to comprise both 5- and 6-methyl isomers. The fractional abundances of the six 6-methyl brGDGTs correlate positively with each other, suggesting a common biological source in most soils, and correlate strongly with soil pH. The presence of the 6-methyl brGDGTs introduced scatter in the original MBT′/CBT-MAT calibration and caused a dependence on soil pH of the MBT′. Exclusion of the 6-methyl brGDGTs from the MBT′, i.e. the newly defined MBT′ 5ME , shows that it is no longer related to soil pH. The correlation with MAT is improved, reducing the residual mean error (RMSE) from 6.2 to 4.8 °C. Also, the correlation of the CBT after the exclusion of the 6-methyl brGDGTs (defined as CBT 5ME ) with soil pH slightly improved. Furthermore, the separate quantification of the 6-methyl brGDGTs allows the definition of new indices. The CBT′, which comprises the 6-methyl brGDGTs, is a substantially improved alternative to the CBT 5ME , reducing the RMSE from 0.8 to 0.5 pH units. Also, the accuracy of MAT reconstructions can be improved using a multiple linear regression, the MAT mr , decreasing the RMSE further to 4.6 °C. Furthermore, we introduce an index that allows the reconstruction of MAT in sites where only the ubiquitous brGDGT Ia, IIa and IIIa are present, the MAT mrs . Our results imply that separate quantification of the 6- and 5-methyl brGDGT is essential for accurately quantifying brGDGTs in environmental samples and results in substantially improved MAT and soil pH reconstructions. [ABSTRACT FROM AUTHOR]

Glycerol dibiphytanyl glycerol tetraether ( GDGT) lipids are part of the cellular membranes of Thaumarchaeota, an archaeal phylum composed of aerobic ammonia oxidizers, and are used in the paleotemperature proxy TEX86. GDGTs in live cells possess polar head groups and are called intact polar lipids ( IPL- GDGTs). Their transformation to core lipids ( CL) by cleavage of the head group was assumed to proceed rapidly after cell death, but it has been suggested that some of these IPL- GDGTs can, just like the CL- GDGTs, be preserved over geological timescales. Here, we examined IPL- GDGTs in deeply buried (0.2-186 mbsf, ~2.5 Myr) sediments from the Peru Margin. Direct measurements of the most abundant IPL- GDGT, IPL-crenarchaeol, specific for Thaumarchaeota, revealed depth profiles, which differed per head group. Shallow sediments (<1 mbsf) contained IPL-crenarchaeol with both glycosidic and phosphate head groups, as also observed in thaumarchaeal enrichment cultures, marine suspended particulate matter and marine surface sediments. However, hexose, phosphohexose-crenarchaeol is not detected anymore below 6 mbsf (~7 kyr), suggesting a high lability. In contrast, IPL-crenarchaeol with glycosidic head groups is preserved over timescales of Myr. This agrees with previous analyses of deeply buried (>1 m) marine sediments, which only reported glycosidic and no phosphate-containing IPL- GDGTs. TEX86 values of CL- GDGTs did not markedly change with depth, and the TEX86 of IPL-derived GDGTs decreased only when the proportions of monohexose- to dihexose- GDGTs changed, likely due to the enhanced preservation of the monohexose GDGTs. Our results support the hypothesis that in situ GDGT production and differential IPL degradation in sediments is not substantially affecting TEX86 paleotemperature estimations based on CL- GDGTs and indicates that likely only a small amount of IPL- GDGTs present in deeply buried sediments is part of cell membranes of active archaea. The amount of archaeal biomass in the deep biosphere based on these IPLs may have been substantially overestimated. [ABSTRACT FROM AUTHOR]

Northern peatlands represent a significant global carbon store and commonly originate from Sphagnum moss-dominated wetlands. These ombrotrophic ecosystems are rain fed, resulting in nutrient-poor, acidic conditions. Members of the bacterial phylum Planctomycetes are highly abundant and appear to play an important role in the decomposition of Sphagnum-derived litter in these ecosystems. High-performance liquid chromatography coupled to high-resolution accurate-mass mass spectrometry (HPLC-HRAM/MS) analysis of lipid extracts of four isolated planctomycetes from wetlands of European north Russia revealed novel ornithine membrane lipids (OLs) that are mono-, di-, and trimethylated at the ε-nitrogen position of the ornithine head group. Nuclear magnetic resonance (NMR) analysis of the isolated trimethylornithine lipid confirmed the structural identification. Similar fatty acid distributions between mono-, di-, and trimethylornithine lipids suggest that the three lipid classes are biosynthetically linked, as in the sequential methylation of the terminal nitrogen in phosphatidylethanolamine to produce phosphatidylcholine. The mono-, di-, and trimethylornithine lipids described here represent the first report of methylation of the ornithine head groups in biological membranes. Various bacteria are known to produce OLs under phosphorus limitation or fatty-acid-hydroxylated OLs under thermal or acid stress. The sequential methylation of OLs, leading to a charged choline-like moiety in the trimethylornithine lipid head group, may be an adaptation to provide membrane stability under acidic conditions without the use of scarce phosphate in nutrient-poor ombrotrophic wetlands. [ABSTRACT FROM AUTHOR]

Abstract: A Siberian peat contains a high abundance of three unknown isomers of hexamethylated branched (br) GDGTs, of which two are present as a second peak eluting shortly after the known hexamethyl br GDGT containing two 5,13,16-trimethyloctacosanyl moieties. Tandem high performance liquid chromatography–mass spectrometry (HPLC–MS2) did not reveal substantial differences in the MS2 spectrum of the two peaks. HPLC isolation of the two peaks of the hexamethylated br GDGT followed by ether cleavage and GC–MS characterization of the hydrocarbons formed, using supersonic molecular beam (SMB) ionization, revealed the second peak to be composed mainly of a novel hexamethyl br GDGT, possessing two 6,13,16-trimethyloctacosanyl moieties. In addition, both chromatographically separated hexamethylated br GDGTs contained a smaller quantity (20–33%) of a non-symmetrical isomer, with one 13,16-dimethyloctacosanyl and one tetramethyloctacosanyl (either 5,13,16,24- or 6,13,16,23-) moiety. Hexamethylated br GDGTs thus consist of four structural isomers. Furthermore, the pentamethylated br GDGT was also isolated and shown to contain both 5,13,16- and 6,13,16-trimethyloctacosanyl moieties, so is composed of two structural isomers. The assignments reveal why environmental distributions of br GDGTs are sometimes complex, which may have implications for the use of br GDGTs in palaeoclimate reconstruction. [Copyright &y& Elsevier]

Abstract: Glycerol dialkyl glycerol tetraether (GDGT) lipids are membrane lipids which were long thought to be synthesized mainly by archaea, organisms thought to be limited to extreme environments. Analysis of environmental samples over the last decade has shown, however, that their structural diversity and sources are much wider than anticipated and that they occur ubiquitously in a wide range of environments, such as oceans and lakes, and their (sub)surface sediments, as well as soils. Several GDGTs have been unambiguously identified and can be used as biomarker lipids, since they are preserved in immature sediments <140Ma. Close examination of the distributions has led to the discovery that GDGTs might be used as proxies for certain environmental parameters, such as the input of soil organic matter to marine environments, soil pH, air temperature and sea and lake water temperature. Here, we review the progress made over the last decade in the analysis, occurrence and recognition of sources of GDGTs, their applications as biomarker lipids, and the development and application of proxies based on their distributions. [Copyright &y& Elsevier]

Abstract: The TEX86 is a proxy based on a ratio of pelagic archaeal glycerol dibiphytanyl glycerol tetraether lipids (GDGTs), and used for estimating past sea water temperatures. Concerns exist that in situ production of GDGTs lipids by sedimentary Archaea may affect its validity. In this study, we investigated the influence of benthic GDGT production on the TEX86 by analyzing the concentrations and distributions of GDGTs present as intact polar lipids (IPLs) and as core lipids (CLs) in three sediment cores deposited under contrasting redox conditions across a depth range from 900 to 3000m below sea level in and below the Arabian Sea oxygen minimum zone (OMZ). Direct analysis of IPLs with crenarchaeol as CL via HPLC/ESI-MS2 revealed that surface sediments in the OMZ were relatively depleted in the phospholipid hexose, phosphohexose (HPH)-crenarchaeol compared to suspended particulate matter from the water column, suggesting preferential and rapid degradation of this IPL. In sediment cores recovered from deeper, more oxic environments, concentrations of HPH-crenarchaeol peaked at the surface, probably due to in situ production by ammonia-oxidizing Archaea, followed by a rapid decrease with increasing depth. No surface maximum was observed in the sediment core from within the OMZ. In contrast, the glycolipids, monohexose-crenarchaeol and dihexose-crenarchaeol, did not change in concentration with depth in the sediment, indicating that they were relatively well preserved and likely mostly derived from fossil pelagic GDGTs. These results suggest that phospholipids are more sensitive to degradation, while glycolipids might be preserved over longer time scales, in line with previous incubation and modeling studies. Furthermore, in situ produced IPL-GDGTs did not accumulate as IPLs, and did not influence the CL-TEX86. This suggests that in-situ produced GDGT lipids were more susceptible to degradation than fossil CL and IPL and did not accumulate as CL. In agreement, no significant changes of TEX86 with sediment depth in the core lipids were observed. However, consistent differences between IPL-derived TEX86 and CL-TEX86 were found. These could be explained by a different composition of CL-GDGT of the glyco- and phospholipids, in combination with dissimilar degradation rates of phospholipids vs. glycolipids. We also observed consistent differences in both IPL-derived and CL-TEX86 between the different cores, equivalent to 3°C when converted to temperature, despite the proximity of the core locations. These differences may potentially be due to a larger addition of GDGTs produced in deeper, colder waters to the (sub)surface-derived GDGTs for the deeper core sites. [Copyright &y& Elsevier]

We characterized and quantified the intact polar lipid (IPL) composition of the surface waters of the North Sea and investigated its relationships with environmental conditions, microbial abundances, and community composition. The total IPL pool comprised at least 600 different IPL species in seven main classes: the glycerophospholipids phosphatidylcholine (PC), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE); the sulfur-bearing glycerolipid sulfoquinovosyldiacylglycerol (SQDG); and the nitrogen-bearing betaine lipids diacylglyceryl-trimethylhomoserine (DGTS), diacylglyceryl-hydroxymethyltrimethylalanine (DGTA), and diacylglyceryl-carboxyhydroxymethylcholine (DGCC). Although no significant relationships were found between the IPL composition and environmental parameters, such as nutrient concentrations, distance-based ordination yielded distinct clusters of IPL species, which could in turn be tentatively correlated with the predominant microbial groups. SQDGs and PGs, as well as PC species containing saturated fatty acid moieties, were related to picoeukaryote abundances and PC species with polyunsaturated fatty acid (PUFA) moieties to nanoeukaryote abundances. The PEs were likely of mixed cyanobacterial--bacterial origin, whereas DGTA and DGCC species were mainly associated with cyanobacteria. DGTSs were likely derived from either pico- or nanoeukaryotes, although the DGTS species with PUFAs also showed some relationship with cyanobacterial abundances. Concentrations of the algal-derived IPLs showed strong positive correlations with chlorophyll a concentrations, indicating they may be used as biomarkers for living photosynthetic microbes. However, direct relationships between the IPLs and microbial groups were relatively weak, implying that the predominant IPLs in marine surface waters are not derived from single microbial groups and that direct inferences of microbial community compositions from IPL compositions should be considered with care. [ABSTRACT FROM AUTHOR]

Abstract: The traditional paradigm that rivers and terrestrial run-off are the major contributors of nutrients to coastal waters has been challenged by observations that nutrient fluxes originating from coastal aquifer subterranean estuaries can equal or even exceed that of other terrestrial sources. Within a coastal aquifer where organic carbon is scarce and ammonium is abundant, bacteria capable of anaerobic ammonium oxidation (anammox bacteria) may play a role in the removal of fixed nitrogen. We investigated the presence of anammox bacteria in a coastal groundwater system (Waquoit Bay, MA USA) using lipid biomarkers. From the distribution of sediment-bound ladderane phospholipids, biomarkers for viable anammox bacteria, we demonstrate the presence of these organisms in association with aqueous chemical transition zones within the aquifer. The distribution of ladderane fatty acids in contrast, provided insight into the historical distribution of anammox bacteria and temporal stability of that distribution. The results suggest that anammox communities have been present over a broad range of depths, most likely determined by changes in the depths of the redox transition zones over time, but that they are more prevalent in the upper portion of the subterranean estuary where ammonium and nitrate coexist. [Copyright &y& Elsevier]

Abstract: Glycerol dibiphytanyl glycerol tetraether-based intact polar lipids (IPL GDGTs) are used as biomarkers for living Archaea and are analyzed utilizing a variety of extraction and quantification techniques. Most IPL GDGT studies have used a modified Bligh–Dyer extraction method, but it has been suggested that Soxhlet extraction may be more efficient for environmental samples and biomass. We investigated the impact of three different extractions (Soxhlet, Bligh–Dyer and accelerated solvent extraction, ASE), two IPL quantification methods and two work up techniques (Na2SO4 and SiO2 column) on the amount and distribution of CL (core lipid)- and IPL-derived GDGTs and crenarchaeol-based IPLs in marine sediments from the Arabian Sea and Icelandic shelf, as well as a microbial mat from a Dutch beach. The different extraction procedures gave a similar yield of CL- and IPL-derived GDGTs. Direct analysis of crenarchaeol IPLs showed, however, that, while GDGTs with a monohexose head group were not affected by the extraction method, there was a large effect on IPL GDGTs containing dihexose or hexose, phosphohexose head groups. Quantification of IPL-derived GDGTs by way of either separation over a silica column or by subtraction of CL GDGTs in the total lipid extract before and after hydrolysis gave similar results, but the ‘subtraction-method’ had a relatively large quantification error. However, the silica column, as well as drying over a Na2SO4 column, resulted in a loss of the hexose, phosphohexose IPLs by up to 80%. Based on the results, a modified Bligh–Dyer extraction with as little further treatment as possible is recommended to allow measurement of the full range of IPL GDGTs in sediments. [Copyright &y& Elsevier]

Abstract: Branched glycerol dialkyl glycerol tetraether lipids (GDGTs) are membrane lipids of soil bacteria that occur ubiquitously in soil, but their occurrence as intact polar lipids (IPLs) has not been well studied. Here, we report the identification and distribution of IPL-branched GDGTs throughout a depth profile of a Swedish peat bog. In addition to two reported glycosidic IPL branched GDGTs, we identified IPL branched GDGTs with a hexose-glycuronic acid, phospho-hexose, or hexose-phosphoglycerol head group, based on mass spectrometry. A selected reaction monitoring (SRM) assay was developed to monitor changes in head group distribution with depth. The abundance of the IPL branched GDGTs increased below the water table, suggesting that they were primarily produced in this part of the peat. This was supported by the concentrations of core lipid and IPL-derived branched GDGTs, which also substantially increased below the water table. However, individual IPL trends differed, which may be due to changes in the microbial community composition with depth or to different degradation rates for the different IPL branched GDGTs. The SRM method was also applied to two different soil types, which showed that similar IPL branched GDGTs as those in peat were present, albeit with different distributions. [Copyright &y& Elsevier]

Glycerol dibiphytanyl glycerol tetraether (GDGT)-based intact membrane lipids are increasingly being used as complements to conventional molecular methods in ecological studies of ammonia-oxidizing archaea (AOA) in the marine environment. However, the few studies that have been done on the detailed lipid structures synthesized by AOA in (enrichment) culture are based on species enriched from nonmarine environments, i.e., a hot spring, an aquarium filter, and a sponge. Here we have analyzed core and intact polar lipid (IPL)-GDGTs synthesized by three newly available AOA enriched directly from marine sediments taken from the San Francisco Bay estuary ("Candidatus Nitrosoarchaeum limnia"), and coastal marine sediments from Svalbard, Norway, and South Korea. Like previously screened AOA, the sedimentary AOA all synthesize crenarchaeol (a GDGT containing a cyclohexane moiety and four cyclopentane moieties) as a major core GDGT, thereby supporting the hypothesis that crenarchaeol is a biomarker lipid for AOA. The IPL headgroups synthesized by sedimentary AOA comprised mainly monohexose, dihexose, phosphohexose, and hexose-phosphohexose moieties. The hexose-phosphohexose headgroup bound to crenarchaeol was common to all enrichments and, in fact, the only IPL common to every AOA enrichment analyzed to date. This apparent specificity, in combination with its inferred lability, suggests that it may be the most suitable biomarker lipid to trace living AOA. GDGTs bound to headgroups with a mass of 180 Da of unknown structure appear to be specific to the marine group I.1a AOA: they were synthesized by all three sedimentary AOA and "Candidatus Nitrosopumilus maritimus"; however, they were absent in the group I.1b AOA "Candidatus Nitrososphaera gargensis." [ABSTRACT FROM AUTHOR]

Abstract: Intact polar lipids (IPLs) are frequently used as biomarkers for living microbial cells and can be separated from core lipids (i.e. lipids without polar headgroups), which are mainly derived from fossil (i.e. dead) cell material, using column chromatography. We have compared the effect of various silica column conditions on the separation and recovery of archaeal glycerol dialkyl glycerol tetraether (GDGT) core lipids, glycolipids and phosphoglycolipids using authentic standards and direct analysis with various high performance liquid chromatography-mass spectrometry (HPLC-MS) techniques. The commonly used procedure to separate these compound classes using dichloromethane, acetone and methanol as eluents, respectively, did not separate core GDGTs from glyco- and phosphoglyco-GDGTs. In contrast, a recently described procedure using hexane:ethyl acetate (3:1, v:v), ethyl acetate and methanol achieved both high recovery and successful separation of core GDGTs from the other IPLs. Application of the method to a geothermally heated soil and suspended particulate matter from the North Sea showed that it separates most of the core GDGTs from the other IPLS and that considerable qualitative and quantitative differences can occur between core and IPL-GDGTs. We conclude that the method is therefore appropriate for the separation of intact archaeal IPLs and their fossil analogues. [Copyright &y& Elsevier]

A letter to the editor is presented in response to an article on green sulfur bacteria by M.J.L. Coolen and J.Overmann in a previous issue of the journal.

Abstract: The distribution of glycerol dibiphytanyl glycerol tetraethers (GDGTs), predominantly derived from planktonic Crenarchaeota, were studied in three age-equivalent Pliocene sapropels as well as in the homogeneous intervals, below and above the sapropel. In both the homogeneous intervals and sapropels the dominance of GDGT-0 and crenarchaeol among the GDGTs indicated their origin from planktonic Crenarchaeota as it was found in many other marine sediments. In the homogeneous intervals highest GDGT abundances (normalized to TOC) were measured at the easternmost study Site 967 of the eastern Mediterranean Sea and decreased at the central and western Sites 969 and 964. Within the three studied sapropels large variations in GDGT abundance were observed. The newly established sea surface temperature (SST) proxy, the TEX86 index, derived from GDGTs of planktonic Crenarchaeota was used to estimate past SST. Comparison with previous obtained SST data using the alkenones from haptophyte algae revealed substantial differences. Whereas the U 37 K′-based SSTs were almost constant at ca. 25°C in both the homogeneous intervals and the sapropels, the TEX86-based SSTs were 26–29°C in the homogeneous intervals and decreased to 15–17°C in the sapropels. The TEX86-based SST values outside the sapropel probably reflect summer SST based on a comparison with the present-day Mediterranean Sea. The surprisingly low TEX86-based SST estimates for the sapropels showed similarities with those obtained for the contemporary euxinic Black Sea. The distribution of marine Crenarchaeota in the modern Black Sea, i.e. thriving at the deeper and colder chemocline, suggests that this leads to a reduction in TEX86, resulting in artificially low SST estimates. A similar situation is inferred for the Pliocene eastern Mediterranean during sapropel deposition since the SST anomaly co-occurs with the build-up of a shallow chemocline. [Copyright &y& Elsevier]

Abstract: Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) are specific membrane lipids derived from archaea, one of the three domains of life. These lipids can be used as biomarkers in paleo-ecological studies. GDGTs can be analyzed by high performance liquid chromatography (HPLC)/mass spectrometry (MS). To quantify GDGTs, external standard curves were run monthly on the HPLC/MS. However, external standard curves represented a snapshot and do not adjust for changes during storage, dissolution and manipulation of samples or drifts in HPLC/MS conditions. To measure absolute GDGT abundances more accurately, we tested the use of a newly synthesized C46 GDGT as an internal standard. The accuracy in the determination of GDGT concentration improved significantly when using the internal standard (5% standard deviation) compared to that obtained with the monthly external standard curve (43% standard deviation). Thus, the new internal standard technique will greatly improve the accuracy of GDGT abundance measurements, increase the potential of GDGTs in paleo-ecological studies. [Copyright &y& Elsevier]

Anammox bacteria present in wastewater treatment systems and marine environments are capable of anaerobically oxidizing ammonium to dinitrogen gas. This anammox metabolism takes place in the anammoxosome which membrane is composed of lipids with peculiar staircase-like ‘ladderane’ hydrocarbon chains that comprise three or four linearly concatenated cyclobutane structures. Here, we applied high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to elucidate the full identity of these ladderane lipids. This revealed a wide variety of ladderane lipid species with either a phosphocholine or phosphoethanolamine polar headgroup attached to the glycerol backbone. In addition, in silico analysis of genome data gained insight into the machinery for the biosynthesis of the phosphocholine and phosphoethanolamine phospholipids in anammox bacteria. [ABSTRACT FROM AUTHOR]

Abstract: High performance liquid chromatography with photodiode array UV–Vis detection and atmospheric pressure chemical ionization mass spectrometry was used to analyze sediment samples from the meromictic Ace Lake (Antarctica), as well as a Pliocene sapropel from the Mediterranean Sea and a Miocene marl from the Vena del Gesso formation (Italy). The Ace Lake samples contained intact chlorobactene, isorenieratene, γ- and β-carotene and two series of carotenoid breakdown products. The first and more abundant series was identified as aryl (ϕ)-carotenals of increasing chain length (C13, C15, C18, C20, C22, C25, C27, C30, and C32) on the basis of their UV–Vis and mass spectra. They appear to be formed from chlorobactene through oxidative cleavage of the double bonds of the polyene chain. The minor series (β-carotenals) was also identified, and may be formed from γ-carotene in a similar manner. Intact isorenieratene and the ϕ-carotenal series were also found in the Mediterranean Sea sapropel. Only a trace of the C32 ϕ-carotenal could be detected, suggesting isorenieratene as the predominant source of these ϕ-carotenals. Additionally, intact β-carotene and C13–C30 β-carotenals were found in the sapropel. The absence of the C32 β-carotenal strongly suggests these breakdown products are derived from β-carotene. The Vena del Gesso marl contained both intact isorenieratene and the C13–C25 ϕ-carotenals. The absence of the longer chain length ϕ-carotenals from this sample may indicate more advanced oxidation of isorenieratene. The carotenals are likely formed during storage of samples and/or extracts under non-ideal conditions, i.e., not frozen and exposed to oxygen although they may also be formed by diagenetic processes. They can be relatively abundant and sometimes be an order of magnitude higher in concentration than the parent carotenoid. Hence, not including the ϕ-carotenals could lead to an underestimation of the persistence of photic zone euxinia. [Copyright &y& Elsevier]

Post-glacial Ace Lake (Vestfold Hills, Antarctica), which was initially a freshwater lake and then an open marine system, is currently a meromictic basin with anoxic, sulfidic and methane-saturated bottom waters. Lipid and 16S ribosomal RNA gene stratigraphy of up to 10,400-year-old sediment core samples from the lake revealed that these environmentally induced chemical and physical changes caused clear shifts in the species composition of archaea and aerobic methanotrophic bacteria. The combined presence of lipids specific for methanogenic archaea and molecular remains of aerobic methanotrophic bacteria (13C-depleted Δ8(14)-sterols and 16S rRNA genes) revealed that an active methane cycle occurred in Ace Lake during the last 3000 calendar years and that the extant methanotrophs were most likely introduced when it became a marine inlet (9400 y BP); rDNA sequences of known methanogens were only recovered from the oldest sediments deposited during the freshwater phase. The latter sequences showed 100% sequence similarity with Methanosarcinales species from freshwater environments and were the source of sn-2- and sn3-hydroxyarchaeols. Archaeal phylotypes related to uncultivated Archaea associated with various marine environments were recovered from the present-day anoxic water column and sediments deposited during the meromictic and marine period. [Copyright &y& Elsevier]

We propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high-performance liquid chromatography/mass spectrometry (HPLC/MS). Analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol, the characteristic membrane lipid of non-thermophilic crenarchaeota, which is especially abundant in the marine and lacustrine environment. Based on these findings, an index was developed, the so-called Branched and Isoprenoid Tetraether (BIT) index, based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol. This BIT index was applied to surface sediments from the Angola Basin, where it was shown to trace the outflow of the Congo River. Furthermore, analyses of particulate organic matter from the North Sea showed relatively higher BIT indices in water column particulate organic matter near large river inputs. A survey of globally distributed marine and lacustrine surface sediments shows that the BIT index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable. The new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 Ma old. [Copyright &y& Elsevier]

The Black Sea and the Cariaco Basin are both large, euxinic marine basins in which methane concentrations are high and where anaerobic oxidation of methane (AOM) is an important part of the carbon cycle. AOM can be recognized by lipid biomarkers that are specific to methanotrophic archaea involved and by strongly 13C-depleted isotope compositions consistent with uptake of 13C-depleted methane-derived carbon. The working hypothesis for our investigation was that AOM in both the Black Sea and Cariaco Basin would generate measurable diagnostic biomarkers and isotope depletions. To test this hypothesis, we analyzed particulate matter and surface sediments for intact glycerol dialkyl glycerol tetreaethers (GDGTs), components of archaeal membrane lipids, and measured stable carbon isotope compositions of their constituent biphytanes. Several GDGTs and strongly 13C-depleted biphytanes indicative of AOM were present in the deep anoxic region of the Black Sea (>700 m). Unexpectedly, this biomarker signal was not detected in the upper anoxic zone of the Black Sea or in the entire water column of the Cariaco Basin, even though previous studies had shown high rates of AOM to occur in both basins. It is possible that the AOM-derived biomarker signal is masked by archaeal lipids derived from non-methanotrophic archaea which utilize 13C-enriched carbon substrates. Alternately we speculate that the methanotrophic community may be highly diverse in euxinic basins, possibly producing another suite of biomarkers that we did not measure. This conclusion will require further testing by coordinated organic geochemical–microbial ecology studies. [Copyright &y& Elsevier]

Recently we proposed a new organic sea surface temperature proxy, TEX86, based on the distribution of archaeal tetraether lipids. Here, we have examined the effect of oxic degradation and maturity on this new temperature proxy. Our results show that oxic degradation does not appear to affect the TEX86 values within the analytical error. Hydrous pyrolysis experiments suggest that thermal maturity does have an effect on TEX86. Sediments with relatively high amounts of 22S-hopanes [22S/(22S+22R) ratios > 0.1] or 17α,21β(H)-hopanes [ββ/(ββ+αβ+βα) ratios <0.5] may have TEX86 values which are biased towards lower values and, thus, lower sea surface temperatures. [Copyright &y& Elsevier]

The middle Cretaceous (125-88 Ma) greenhouse world was characterized by high atmospheric CO[sub 2] levels, the general absence of polar ice caps, and much higher global temperatures than at present. Both δ[sup 18]O-based and model-based temperature reconstructions indicate extremely high sea-surface temperatures (SSTs) at high latitudes. However, there are a number of uncertainties with SST reconstructions based on δ[sup 18]O isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the δ[sup 18]O value of Cretaceous seawater, the paleoecology of middle Cretaceous marine organisms and seawater pH. Here we applied a novel SST proxy (i.e., TEX[sub 86] [tetraether index of 86 carbon atoms], based on the membrane lipids of marine crenarchaeota) derived from middle Cretaceous sedimentary rocks deposited at low latitudes. The TEX[sub 86] proxy indicates that tropical SSTs in the proto-North Atlantic were at 32-36 °C during the early Aibian and late Cenomanian-early Turonian. This finding agrees with SST estimates based on δ[sup 18]O paleothermometry of well-preserved foraminifera as well as global circulation model calculations. The TEX[sub 86] proxy indicates cooler SSTs (27-32 °C) for the equatorial Pacific during the early Aptian, which is in agreement with SST estimates based on δ[sup 18]O paleothermometry. [ABSTRACT FROM AUTHOR]

It has recently been shown that membrane lipids of marine crenarchaeota, a ubiquitous and abundant component of plankton, occur in relatively high concentrations in recent and ancient sediments. In this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments. We especially focussed on temperature, as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature. Indeed, a significant linear correlation (r2=0.92) is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures. This suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives. In turn, archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments. [Copyright &y& Elsevier]

Repeated semi-preparative normal-phase HPLC was performed to isolate selected biomarkers from sediment extracts for radiocarbon analysis. Flow injection analysis–mass spectrometry was used for rapid analysis of collected fractions to evaluate the separation procedure, taking only 1 min per fraction. In this way 100–1000 μg of glycerol dialkyl glycerol tetraethers, sterol fractions and chlorophyll-derived phytol were isolated from typically 100 g of marine sediment, i.e., in sufficient quantities for radiocarbon analysis, without significant carbon isotopic fractionation or contamination. [Copyright &y& Elsevier]

Carotenoids were analysed in ca. 1-cm thick subsamples of three laterally time-equivalent sapropels from a west–east transect of the eastern Mediterranean Basin to study euxinic periods during Pliocene sapropel formation. The amount of intact isorenieratene (summed all-trans and cis isomers), ranged from non-detectable at the base and top of a sapropel up to 140 μg/g sediment in the central parts. Isorenieratene accumulation rates at the central and western site are remarkably similar and increase sharply to levels of up to 3.0 mg m−2 yr−1 in the central part of the sapropel and then drop to low levels. This pattern indicates an expansion of euxinic conditions reaching into the photic zone, followed by deepening of the chemocline during deposition of this Pliocene sapropel. The sapropel from the easternmost site of the basin, which contains less organic carbon, shows much lower isorenieratene accumulation rates and even absence of isorenieratene in the central part of the sapropel. Ba/Al ratios indicate enhanced palaeoproductivity during sapropel formation, supporting previously proposed models, according to which increased productivity is the driving force for the generation of euxinic conditions. [Copyright &y& Elsevier]

Confirms the widespread occurrence of known and newly identified membrane lipids, isoprenoid glycerol dialkyl tetraethers (GDGT) and branched glycerol dialkyl diethers, in low-temperature environments. Structure of the GDGT; Novel types of GDGT identified; Origin and distribution.

• Reversed phase UHPLC-ESI/HRMS2 detects a broad range of (novel) bacteriohopanepolyols. • BHPs are detected simultaneously with intact polar lipids. • The nucleoside of adenosylhopane type-3 is a methylated adensine. • The nucleoside of adenosylhopane type-2 is N1-methylinosine. Bacteriohopanepolyols (BHPs) are lipids with great chemotaxonomic potential for microbial populations and biogeochemical processes in the environment. The most commonly used methods for BHP analysis are chemical degradation followed by gas chromatography-mass spectrometry (MS) or derivatization followed by high performance liquid chromatography (HPLC)-atmospheric pressure chemical ionization/MS. Here we report on significant advances in the analysis of non-derivatized BHPs using U(ltra)HPLC-electrospray ionization-high resolution MS2. Fragmentation mass spectra provided information on the BHP core, functionalized side chain, as well as the conjugated moiety of composite BHPs. We successfully identified the common bacteriohopanepolyols and their (di)methylated and (di)unsaturated homologues, aminoBHPs, and composite BHPs (e.g., cyclitol ethers and methylcarbamate-aminoBHPs) in biomass of several known BHP-producing bacteria. To show how the method can be exploited to reveal the diversity of BHPs in the environment, we investigated a soil from an active methane seep, in which we detected ca. 130 individual BHPs, including a complex distribution of adenosylhopanes. We identified the nucleoside base moiety of both adenosylhopane type-2 and type-3. Adenosyl hopane type-3 contains a methylated adenine as its nucleobase, while type-2 appears to contain a deaminated and methylated adenine, or N1-methylinosine. In addition, we detected novel adenosylhopanes. Furthermore, we identified a series of novel composite BHPs comprising of bacteriohopanepolyols conjugated to an ethenolamine moiety. The novel ethenolamineBHPs as well as aminoBHPs were also detected acylated to fatty acids. The analytical approach described allows for simultaneous analysis of the full suite of IPLs, now including BHPs, and represents a further step towards environmental lipidomics. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a novel method, based on high performance liquid chromatography–mass spectrometry, for the rapid and quantitative analysis of levoglucosan in geological samples. Compared with existing methods, it does not require derivatization or extensive work up, and requires less sample material. Its validity is demonstrated by way of application to soil samples collected from a burned dune area and a late Quaternary marine sediment. [Copyright &y& Elsevier]

Sapropels are organic-rich sediment layers deposited in the eastern Mediterranean Sea during precession minima, resulting from an increase in export productivity and/or preservation. Increased freshwater delivery from the African continent resulted in stratification, causing deepwater anoxia, while nutrient input stimulated productivity, presumably at the deep chlorophyll maximum. Previous studies have suggested that during sapropel deposition, nitrogen fixation was widespread in the highly stratified surface waters, and that cyanobacteria symbiotic with diatoms (diatom-diazotroph associations, DDAs) were responsible. Here we analyzed sapropel S5 sediments for heterocyst glycolipids (HGs) from three locations in the eastern Mediterranean. HG biomarkers can differentiate between those heterocystous cyanobacteria that are free living (found predominately in freshwater or brackish environments) and those that are from DDAs (found in marine settings). In our primary core, from a location which would have been influenced by the Nile River outflow, we detected a HG with a pentose (C5) head group specific for DDAs. However, HGs with a hexose (C6) head group, specific to free-living cyanobacteria, were present in substantially (up to 60×) higher concentration. These data suggest that at our study location, free-living cyanobacteria were the dominant diazotrophs, rather than DDAs. The C6 HGs increased substantially at the onset of sapropel S5 deposition, suggesting that substantial seasonal cyanobacterial blooms were associated with a brackish surface layer flowing from the Nile into the eastern Mediterranean. Two additional S5 sapropels were analyzed, one also from the Nile delta region and one from the region between Libya and southwestern Crete. Overall, comparison of the HG distribution in the three S5 sapropels provides evidence that all three locations were initially influenced by surface salinities that were sufficiently low to support free-living heterocystous cyanobacteria. While free-living heterocystous cyanobacteria continued to outnumber DDAs during sapropel deposition at the two Nile-influenced sites, DDAs, indicators of persistent marine salinities, were the dominant diazotrophs in the upper part of the sapropel at the more westerly site. These results indicate that N2 fixation by free-living cyanobacteria offers an important additional mechanism to stimulate productivity in regions with strong river discharge during sapropel deposition. [ABSTRACT FROM AUTHOR]

• Suspended particular matter from Lake Malawi was analyzed for isoprenoid GDGTs. • HPH-crenarchaeol concentrations were greatest just below the chlorophyll maximum. • Maximum CL concentrations likely reflect degradation of recently produced IPL GDGTs. • A second, deeper-dwelling Thaumarchaeotal population exists near the chemocline. Several long paleoclimate records generated from Lake Malawi sediments rely on an assumption that the TEX 86 paleothermometer reflects annual mean lake surface temperatures. Thaumarchaeota, the producers of the isoprenoid glycerol dialkyl glycerol tetraether (iGDGT) lipids that are the basis of the TEX 86 proxy, can occupy a wide range of habitats in the upper water column of lacustrine systems, so it is crucial to specifically constrain the ecology of Thaumarchaeota in Lake Malawi to properly interpret its sedimentary TEX 86 record. To investigate the spatial and vertical distribution of Thaumarchaeotal iGDGT production in Lake Malawi, suspended particulate matter (SPM) was collected from the upper water column (>300 m) at three sites spanning the north, central, and south basins of the lake and analyzed for intact polar (IPL) and core (CL) iGDGT lipid abundances. Samples were collected in January during the austral summer when the lake is strongly stratified. Concentrations of the most labile IPL, hexose-phosphohexose (HPH)-crenarchaeol, were greatest just below the deep chlorophyll maximum at ∼50 m water depth in the deeper north and central basins and ∼30 m in the shallow south basin. Maximum CL concentrations occur below the maximum HPH-crenarchaeol concentrations and therefore possibly reflect the accumulation of recently produced IPL GDGT degradation products. If the export of CLs to the sediments is dominated by this CL pool, sedimentary TEX 86 would reflect Thaumarchaeota living within the thermocline during the stratified season and therefore may have a cool bias rather than reflecting true surface water temperatures. An increase in abundances of GDGT-2, crenarchaeol isomer, and monohexose (MH)-crenarchaeol at ∼150–200 m suggests that a secondary Thaumarchaeotal population, likely Group I.1b Thaumarchaeota, inhabits the subsurface water column near the anoxic-suboxic boundary. Total production of iGDGTs by this group appears to be much lower than the surface-dwelling clade, but its imprint on sedimentary TEX 86 is unknown. An analysis of iGDGT production in the water column throughout the annual cycle is needed to resolve the timing and magnitude of export of CLs to the sediments from these two Thaumarchaeotal populations. [ABSTRACT FROM AUTHOR]

Highlights • Dominant di-unsaturated C 40 alkenone observed in Late Cretaceous sediments. • Cretaceous GDGT distributions similar to modern-day confirming TEX 86 consistency. • Diagenetic conversion of GDGTs into the GDDs has no apparent effect on TEX 86. • Unusual long-chain diol distributions observed before Miocene, compromising LDI. • Long-chain keto-ols have same distributions as diols suggesting diagenetic link. Abstract We evaluated changes in the distributions of long-chain alkenones, long-chain diols and GDGTs, lipids commonly used for paleothermometry, over the last 90 Myrs for sediments deposited on the New Jersey shelf (the Bass River site) and assessed potential effects of different ancestral producers and diagenesis on their distributions and their impact on the associated temperature proxies. As reported before, the Paleogene distributions of alkenones are generally similar to those in modern haptophytes, but unusual alkenone distributions, characterized by a dominant di-unsaturated C 40 alkenone, are observed for Late Cretaceous sediments, suggesting different ancestral source organisms for alkenones in this interval. The isoprenoid GDGT distributions remained comparable to modern-day distributions, suggesting that TEX 86 can be applied up to ca. 90 Ma. The Miocene long-chain diol distributions are similar to modern-day distributions, but the older sediments reveal unusual distributions, dominated by the C 28 1,12- and C 26 1,13-diols, suggesting different source organisms before ∼30 Ma. Accordingly, the LDI does not match other paleotemperature proxies, suggesting its applicability might be compromised for sediments older than the Miocene. Our results indicate that of the three proxies, the TEX 86 seems to be the most applicable for deep time temperature reconstructions. [ABSTRACT FROM AUTHOR]

Archaea are important players in marine biogeochemical cycles, and their membrane lipids are useful biomarkers in environmental and geobiological studies. However, many archaeal groups remain uncultured and their lipid composition unknown. Here, we aim to expand the knowledge on archaeal lipid biomarkers and determine the potential sources of those lipids in the water column of the euxinic Black Sea. The archaeal community was evaluated by 16S rRNA gene amplicon sequencing and by quantitative PCR. The archaeal intact polar lipids (IPLs) were investigated by ultra‐high‐pressure liquid chromatography coupled to high‐resolution mass spectrometry. Our study revealed both a complex archaeal community and large changes with water depth in the IPL assemblages. In the oxic/upper suboxic waters (<105 m), the archaeal community was dominated by marine group (MG) I Thaumarchaeota, coinciding with a higher relative abundance of hexose phosphohexose crenarchaeol, a known marker for Thaumarchaeota. In the suboxic waters (80–110 m), MGI Nitrosopumilus sp. dominated and produced predominantly monohexose glycerol dibiphytanyl glycerol tetraethers (GDGTs) and hydroxy‐GDGTs. Two clades of MGII Euryarchaeota were present in the oxic and upper suboxic zones in much lower abundances, preventing the detection of their specific IPLs. In the deep sulfidic waters (>110 m), archaea belonging to the DPANN Woesearchaeota, Bathyarchaeota, and ANME‐1b clades dominated. Correlation analyses suggest that the IPLs GDGT‐0, GDGT‐1, and GDGT‐2 with two phosphatidylglycerol (PG) head groups and archaeol with a PG, phosphatidylethanolamine, and phosphatidylserine head groups were produced by ANME‐1b archaea. Bathyarchaeota represented 55% of the archaea in the deeper part of the euxinic zone and likely produces archaeol with phospho‐dihexose and hexose‐glucuronic acid head groups. [ABSTRACT FROM AUTHOR]