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Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane-spanning lipids from Bacteria and Archaea that are ubiquitous in a range of natural archives and especially abundant in peat. Previous work demonstrated that the distribution of bacterial branched GDGTs (brGDGTs) in mineral soils is correlated to environmental factors such as mean annual air temperature (MAAT) and soil pH. However, the influence of these parameters on brGDGT distributions in peat is largely unknown. Here we investigate the distribution of brGDGTs in 470 samples from 96 peatlands around the world with a broad mean annual air temperature (-8 to 27 degrees C) and pH (3-8) range and present the first peat-specific brGDGT-based temperature and pH calibrations. Our results demonstrate that the degree of cyclisation of brGDGTs in peat is positively correlated with pH, pH = 2.49 x CBTpeat + 8.07 (n = 51, R-2 = 0.58, RMSE = 0.8) and the degree of methylation of brGDGTs is positively correlated with MAAT, MAAT(peat) (degrees C) = 52.18 x MBT'(5me) - 23.05 (n = 96, R-2 = 0.76, RMSE = 4.7 degrees C). These peat-specific calibrations are distinct from the available mineral soil calibrations. In light of the error in the temperature calibration (similar to 4.7 degrees C), we urge caution in any application to reconstruct late Holocene climate variability, where the climatic signals are relatively small, and the duration of excursions could be brief. Instead, these proxies are well-suited to reconstruct large amplitude, longer-term shifts in climate such as deglacial transitions. Indeed, when applied to a peat deposit spanning the late glacial period (similar to 15.2 kyr), we demonstrate that MAAT(peat) yields absolute temperatures and relative temperature changes that are consistent with those from other proxies. In addition, the application of MAAT(peat) to fossil peat (i.e. lignites) has the potential to reconstruct terrestrial climate during the Cenozoic. We conclude that there is clear potential to use brGDGTs in peats and lignites to reconstruct past terrestrial climate. (C) 2017 The Authors. Published by Elsevier Ltd.

The history of the Amazon River is a much-discussed subject, and the timing of the development of a transcontinental system in particular is a matter of some controversy, with estimations varying between the Early Miocene and the Pliocene or even the Pleistocene. To shed further light on this, we studied the sediment provenance of an Oligocene to Late Pleistocene marine sedimentary section from the Ceara Rise (ODP Site 925), a topographic high in the central Atlantic Ocean, using major element concentrations and Nd isotopic composition in 85 samples. In addition, the carbon isotopic composition of bulk organic matter and changes in the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) were used to identify periods of increased river outflow. On the basis of these results, we suggest that the history of the development of the Amazon River is characterized by specific steps. During the late Oligocene/Early Miocene (30–18.3 Ma), the terrigenous mass accumulation rates (TARs) were high, and sediment and GDGT compositions suggest that a large river system existed, which at times received weathering products from a younger and probably Andean sediment source. A shift to a younger Andean sediment provenance after 8.7 Ma indicates that the Amazon River became permanently connected with the Andes. Between 18.3 and 4.5 Ma, TARs were generally low, and GDGTs were derived for the most part from in situ production in marine waters. Around 4.5 Ma, the river expanded, probably due to ongoing tectonic activity, and uplift in the Andes increased Andean rock erosion. This led to a strong increase in terrigenous sediment deposition and enhanced organic matter preservation on the Ceara Rise, and the delivery of terrestrial (both soil and riverine) branched GDGTs to the Ceara Rise.

The abundance and composition of glycerol dibiphytanyl glycerol tetraether (GDGT) and glycerol tribiphytanyl glycerol tetraether (GTGT) lipids were determined as a function of growth phase as a proxy for nutrient availability, the pH of growth medium, and incubation temperature in cultures of the thermoacidophile Picrophilus torridus. Regardless of the cultivation condition, the abundance of GDGTs and GTGTs was greater in the polar than core fraction, with a marked decrease in core GDGTs in cultures harvested during log phase growth. These data are consistent with previous suggestions indicating that core GDGTs are re-functionalized during polar lipid synthesis. Under all conditions examined, polar lipids were enriched in a GDGT with 2 cyclopentyl rings (GDGT-2), indicating GDGT-2 is the preferred lipid in this taxon. However, lag or stationary phase grown cells or cells subjected to pH or thermal stress were enriched in GDGTs with 4, 5, or 6 rings and depleted in GDGTs with 1, 2, 3, rings relative to log phase cells grown under optimal conditions. Variation in the composition of polar GDGT lipids in cells harvested during various growth phases tended to be greater than in cells cultivated over a pH range of 0.3 to 1.1 and a temperature range of 53°C to 63°C. These results suggest that the growth phase, the pH of growth medium, and incubation temperature are all important factors that shape the composition of tetraether lipids in Picrophilus. The similarity in enrichment of GDGTs with more rings in cultures undergoing nutrient, pH, and thermal stress points to GDGT cyclization as a generalized physiological response to stress in this taxon.

Rice constitutes one of the most important staple foods for more than half of the World’s population. Typical wet rice field management includes ploughing and puddling of soils under submergence as well as alternate flooding and draining of fields, processes that initiate the development of so-called paddy soils. On global scale paddy soils may evolve on most different soil substrates. Soil redox-conditions associated with paddy management are considered to diminish decomposition rates of soil organic matter (SOM), which in favours its accumulation as well as the emission of greenhouse gases. Hence, it is of paramount importance to study the effect of wetland rice cultivation on biogeochemical processes. Due to the large spatial extent of and high carbon turnover in rice paddies their role in global carbon cycling as carbon (CO2) sinks or sources needs to be investigated. Up to now, biogeochemical cycling in such agroecosystems has been investigated intensively, whereas molecular lipid biomarker studies remained scarce. This dissertation aimed at a comprehensive study of management-induced effects on lipid influx into paddy soils and subsequent lipid evolution under the environmental conditions prevailing. A crucial finding was that management and climatic conditions dramatically influenced the lipid composition in paddy compared to upland (non-paddy) soils. In this context, recurring anaerobic conditions due to periodical submergence of paddy soils had a profound important influence on SOM preservation potential and microbial community structures. Climatic conditions affected biogeochemical lipid cycling to a larger extent than the substrate on which the soil had developed. Accelerated cycling in tropical versus subtropical locations was amply reflected in preservation and composition of plant lipids and microbial membrane lipids. Reis ist eines der wichtigsten Grundnahrungsmittel für mehr als die Hälfte der stetig wachsenden Weltbevölkerung. Die typische Bodenbewirtschaftung eines Reisfeldes umfasst das Nasspflügen, einem Verfahren aus Pflügen unter Wasser und dem anschließenden Abdichten der Bodenoberfläche, welche zusammen zur Herausbildung des sogenannten „paddy soil“ führen. Die mit der paddy Bewirtschaftung in Zusammenhang stehenden Redoxbedingungen im Boden, werden generell mit einer geringeren Zersetzungsrate und der bevorzugten Anreicherung der organischen Bodensubstanz sowie mit der Freisetzung von Treibhausgasen in Verbindung gebracht. Aufgrund der großen Flächenausdehnung und des hohen Kohlenstoffumsatzes von Reisböden ist es besonders für die Erforschung des globalen Kohlenstoffkreislaufes wichtig, zu wissen, ob diese paddy Böden eher als Kohlenstoff-Senke (CO2) oder -Quelle fungieren. Das Ziel dieser Dissertation war es, eine umfassende Studie über den Einfluss der paddy Bodenbewirtschaftung auf den Eintrag und die Entwicklung der Lipidzusammensetzung unter verschiedenen gegebenen Umweltbedingungen zu erhalten. Zu den wichtigsten Ergebnissen dieser Arbeit zählen, dass sowohl die Bewirtschaftung als auch die klimatischen Gegebenheiten die Lipidzusammensetzung im Boden beeinflussen, wie es z.B. in den signifikant unterschiedlichen Ergebnissen von paddy Böden und non-paddy Böden (Agrarböden ohne Nassreisbewirtschaftung) angezeigt wurde. Hierbei spielt die periodische Überflutung der paddy Böden, bei welchen zyklisch anaerobe Bedingungen auftreten, eine zentrale Rolle für die Erhaltung der organischen Bodensubstanz sowie für die Ausbildung der mikrobiellen Vergesellschaftung. Zudem laufen die biochemischen Prozesse in den Tropen deutlich beschleunigter voran als in den Subtropen, was sich auch in der Erhaltung und Zusammensetzung von Pflanzenlipiden und der mikrobiellen Membranlipide widerspiegelte.

We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25 m at all sites and the $$ U_{37}^{{{\text{K}}'}} $$ values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74–99 m depth, and the $$ {\text{TEX}}_{86}^{\text{H}} $$ agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20 m depth was characterized by low GDGT concentrations and low $$ {\text{TEX}}_{86}^{\text{L}} $$ -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX86-based temperatures were nearly constant in the water column deeper than 300 m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons.

Significance Reliable prediction of future climate conditions requires a thorough understanding of climate variability throughout Earth’s history. Microbial molecular fossils, such as bacterial membrane-spanning tetraether lipids [branched glycerol dialkyl glycerol tetraethers (brGDGTs)], have proven to be particularly useful for the assessment of past climatic conditions, because they occur ubiquitously in the environment and show compositional changes related to temperature. However, the identity and ecology of brGDGT-producing bacteria is largely unknown, and a mechanistic basis for brGDGT-based paleoclimate reconstruction is still lacking. Here, we present insights into the ecological parameters that affect brGDGT synthesis in lakes, demonstrating that eutrophic lakes with oxygen-deprived bottom waters are the preferred sites for brGDGT-based reconstructions of continental climate., Terrestrial paleoclimate archives such as lake sediments are essential for our understanding of the continental climate system and for the modeling of future climate scenarios. However, quantitative proxies for the determination of paleotemperatures are sparse. The relative abundances of certain bacterial lipids, i.e., branched glycerol dialkyl glycerol tetraethers (brGDGTs), respond to changes in environmental temperature, and thus have great potential for climate reconstruction. Their application to lake deposits, however, is hampered by the lack of fundamental knowledge on the ecology of brGDGT-producing microbes in lakes. Here, we show that brGDGTs are synthesized by multiple groups of bacteria thriving under contrasting redox regimes in a deep meromictic Swiss lake (Lake Lugano). This niche partitioning is evidenced by highly distinct brGDGT inventories in oxic vs. anoxic water masses, and corresponding vertical patterns in bacterial 16S rRNA gene abundances, implying that sedimentary brGDGT records are affected by temperature-independent changes in the community composition of their microbial producers. Furthermore, the stable carbon isotope composition (δ13C) of brGDGTs in Lake Lugano and 34 other (peri-)Alpine lakes attests to the widespread heterotrophic incorporation of 13C-depleted, methane-derived biomass at the redox transition zone of mesotrophic to eutrophic lake systems. The brGDGTs produced under such hypoxic/methanotrophic conditions reflect near-bottom water temperatures, and are characterized by comparatively low δ13C values. Depending on climate zone and water depth, lake sediment archives predominated by deeper water/low-13C brGDGTs may provide more reliable records of climate variability than those where brGDGTs derive from terrestrial and/or aquatic sources with distinct temperature imprints.

This PhD thesis focused on the analysis and application of microbial membrane lipids as biomarkers in marine sediments. Existing protocols for lipid extraction from marine sediments and biomass were modified. In addition, recent protocols based on high-performance liquid chromatography coupled to mass spectrometry (HPLC-MS) as well as state-of-the-art mass spectrometric analysis by quadrupole time-of-flight (MSqTOF) and the triple quadrupole (MSQQQ) mass spectrometer were used to investigate matrix effects and evaluate the reliability of quantitative analysis in marine environmental samples. The improved lipid extraction and quantification were used to analyze Black Sea water column and sediments samples to a depth of 8 meters from site GeoB 15105 taken during cruise M84/1 (DARCSEAS) with R/V Meteor to apply lipid analysis in benthic bio systems. With this component specific differentiation between planktonic and benthic lipid signature we assessed possible lipid sources. Here, this high detail lipid fingerprinting allowed us to observe changes in the head group and lipid core structures of the intact polar lipids according to the geochemical zonation.

Marine ammonia-oxidizing archaea of the phylum Thaumarchaeota synthesize glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipids that are used as for the reconstruction of sea surface temperatures by means of the TEX86 paleothermometer. Discrepancies between observed and predicted TEX86-temperatures throughout the global ocean indicate that the physiological and ecological controls on lipid composition in planktonic Thaumarchaeota remain poorly understood. In this thesis, the influence of growth phase, temperature, pH, and salinity on the membrane lipid composition of Thaumarchaeota were investigated. The results indicate that TEX86 is not only influenced by temperature but similarly by growth phase and community composition, which compromises its utility as a paleothermometer. A comprehensive study of the lipidomes of 11 thaumarchaeal cultures revealed that Thaumarchaeota contain a high diversity of membrane lipids that is related to phylogeny as well as growth characteristics. This analysis further revealed that all Thaumarchaeota contain the specific biomarkers crenarchaeol, methoxy archaeol, and saturated menaquinone-6.

We report here the development of an analytical protocol for the specific isolation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (i-and br-GDGTs, respectively) of microbial origin from soil samples for radiocarbon dating. This protocol comprises an extraction step followed by several chromatographic steps combining different techniques (silica gel column chromatography, high performance liquid chromatography and thin layer chromatography). Radiocarbon dating of these two series of compounds, isolated from a surface sample and a deep horizon sample (40-50 cm) from a soil profile, shows that i-and br-GDGTs in the deep sample have a comparable mean residence time (MRT), despite their different biological origin. These MRT are, however, lower than those measured for the soil organic matter (SOM) and for the different compartments of SOM. This result suggests that i-and br-GDGTs originate from microorganisms using the same carbon source, made of a combination of ancient and recent organic matter. It can also be envisaged that these compounds originate from both recent and ancient microbial populations. These preliminary results suggest that the use of (palaeo) proxies based on the distributions of GDGTs might be questionable in the case of soils or, at least, that caution is needed when interpreting soil GDGT signals in terms of (palaeo) environmental reconstructions., Nous rapportons dans cette étude le développement d’un protocole analytique pour l’isolement spécifique, à partir d’échantillons de sol, des tétraéthers de diglycérol isoprénoïdes (i-GDGT) et ramifiés (br-GDGT), composés d’origine microbienne, dans le but de procéder à leur datation au 14C. Ce protocole comprend une étape d’extraction de la composante lipidique du sol avec des solvants organiques, suivie d’étapes de séparation et de purification par différentes techniques chromatographiques (chromatographie liquide sur colonne, chromatographie liquide à haute performance et chromatographie sur couche mince). Après isolement, la datation au 14C de ces deux séries de composés dans deux échantillons d’un profil de sol, l’un de surface, l’autre en profondeur (40-50 cm) indique qu’en dépit d’une origine biologique distincte, les i-et br-GDGT présentent des temps moyens de résidence (TMR) similaires en profondeur, TMR qui sont inférieurs à ceux de la matière organique de ce même échantillon et des différents compartiments qui la constituent. Ceci suggère soit que ces lipides proviennent de microorganismes utilisant une même source de carbone constituée d’un mélange d’une matière organique récente et ancienne, à moins qu’ils ne proviennent d’un mélange provenant d’une population ancienne et d’une population plus récente. Quoi qu’il en soit, ces observations préliminaires suggèrent que l’utilisation de (paléo) proxies reposant sur la distribution des GDGT dans le cas des sols est parfois discutable, ou, tout au moins, incitent à la prudence quant à d’éventuelles interprétations dans le cadre de reconstitutions (paléo) environnementales., Courel Blandine, Schaeffer Philippe, Adam Pierre, Ertlen Damien, Schwartz Dominique, Bernasconi Stefano, Hajdas Irka. Analyse, isolement et datation au 14C de lipides dans les sols : l’exemple des tétraéthers de diglycérol. In: Collection EDYTEM. Cahiers de géographie, numéro 18, 2015. Sols et matières organiques. Mémoires et héritages. pp. 57-68.

We investigated microbial life preserved in a hydrothermally inactive silica–barite chimney in comparison with an active barite chimney and sediment from the Loki's Castle low-temperature venting area at the Arctic Mid-Ocean Ridge (AMOR) using lipid biomarkers. Carbon and sulfur isotopes were used to constrain possible metabolic pathways. Multiple sulfur (dδ34S, Δ33S) isotopes on barite over a cross section of the extinct chimney range between 21.1 and 22.5 % in δ34S, and between 0.020 and 0.034 % in Δ33S, indicating direct precipitation from seawater. Biomarker distributions within two discrete zones of this silica–barite chimney indicate a considerable difference in abundance and diversity of microorganisms from the chimney exterior to the interior. Lipids in the active and inactive chimney barite and sediment were dominated by a range of 13C-depleted unsaturated and branched fatty acids with δ13C values between -39.7 and -26.7 %, indicating the presence of sulfur-oxidizing and sulfate-reducing bacteria. The majority of lipids (99.5 %) in the extinct chimney interior that experienced high temperatures were of archaeal origin. Unusual glycerol monoalkyl glycerol tetraethers (GMGT) with 0–4 rings were the dominant compounds suggesting the presence of mainly (hyper-) thermophilic archaea. Isoprenoid hydrocarbons with δ13C values as low as -46 % also indicated the presence of methanogens and possibly methanotrophs.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility 63- 4C when translated to temperature) but a large spread in BIT measurements (reproducibility 60.41 on a scale of 0-1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the ''true'' (i.e., molarbased) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.

Sea surface temperature (SST), at the interface between the atmosphere and the ocean, is an important element in the global climate system. Accurate estimates of past SSTs are indispensable for studying global climate and for validating the numerical models used for projections of future climate. SSTs prior to the instrumentation era could be reconstructed using climatically sensitive biomarkers such as alkenones and glycerol dialkyl glycerol tetraethers (GDGTs). Herein I use marine sediments, both core-tops and long piston cores, to further examine the applicability of organic SST proxies derived from the aforementioned biomarkers, with an emphasis on the relatively under-studied subantarctic Southeast Pacific. The appraisal of these proxies is based on the correlation of the core-top proxy index values with present-day climatological SST, and the comparison of the SST records inferred from these proxies with other regional SST records. The alkenone index (UK37 and UK 37) values in the South Pacific core-tops display linear relationships with climatological World Ocean Atlas 2009 (WOA09) SST at low temperatures (1 -12°C), with equally high r2 values (>0.93). These results suggest that both alkenone indices are highly correlated to SST even at high latitudes, rendering them appropriate for reconstructing SST in the subantarctic Pacific. However, these indices yield different Pleistocene SST patterns for study sites in the subantarctic sector of the Southern Ocean. Judging from the better structural fit of UK37 SST records with other subantarctic surface proxy records, including foraminiferal 18O and SST records inferred from diatom- and foraminiferal assemblages, it appears that the UK37 index results in more plausible paleo SST records in this region, as opposed to the commonly used UK 37 index. The GDGT index (TEX86 and TEX86L) values in the subpolar and polar core-tops (with overlying SSTs of -2 to 17°C) are not highly correlated (r2 values < 0.3) to the annual mean WOA09 SST. Plotting these indices against seasonal SSTs and water temperatures at various hydrographic boundaries does not improve the correlation. Nevertheless, when these data are combined with previously published core-top data (n = 630) spanning a SST range of -2 to 30°C, the r2 values of these relationships improve to ~ 0.8, with a better correlation for the TEX86 compared to TEX86L. The TEX86 calibration yields SST estimates that are in better agreement with the WOA09 SST for subpolar and polar regions, rendering it a better SST index in these regions. Meanwhile, applying the GDGT index on a Southeast Pacific sediment core yields SSTs that are colder than those inferred from the alkenones, and the GDGT-derived interglacial SSTs are ~3°C colder than annual mean WOA09 SST. Given the lack of seasonality in the archaeal abundance here, the cold-biased GDGT estimates probably reflect subsurface temperature instead of SST. The three SST records presented here allow for further understanding of the surface oceanographic variability in the subtropical and subantarctic Southeast Pacific over the past 700 kyr. The extent of glacial cooling increases with latitude, up to ~8°C in the subantarctic as opposed to the ~4°C in the subtropics. Intense cooling at high latitudes results in larger latitudinal SST gradients during glacials than interglacials. The alkenone-inferred SSTs along the latitudinal range of the Peru-Chile Current (PCC) imply massive equatorward migrations of the Southern Ocean frontal systems and increased equatorward transport of subantarctic waters owing to a stronger PCC during glacials. In addition, GDGT-derived temperatures suggest enhanced subsurface warming during MIS 11 and 13 in the subtropical Southeast Pacific, plausibly due to water column reorganization analogous to that occurring during modern-day El-Niño conditions.

Centennial-scale records of sea-surface temperature and opal composition spanning the Last Glacial Maximum and Termination 1 (circa 25-6 ka) are presented here from Guaymas Basin in the Gulf of California. Through the application of two organic geochemistry proxies, the U-37(K') index and the TEX86H index, we present evidence for rapid, stepped changes in temperatures during deglaciation. These occur in both temperature proxies at 13 ka (similar to 3 degrees C increase in 270 years), 10.0 ka (similar to 2 degrees C decrease over similar to 250 years) and at 8.2 ka (3 degrees C increase in

Glycerol ether lipids are prominent membrane constituents in Archaea and Bacteria that are characterized by high potential for preservation in geological settings.During the past decade they were increasingly used in molecular proxies. For example,selected glycerol dialkyl glycerol tetraethers (GDGT) are used in ratios such as the TEX86 and BIT index for reconstructing past sea surface temperature (SST) and terrestrial input, respectively. However, the distribution and structural diversity of glycerol ether lipids in marine sediments has not yet been fully explored. In order to obtain a better understanding of the origin and fate of these lipids and to evaluate the potential impact on molecular proxies, a globally distributed set of samples was analyzed in this PhD thesis project. More than forty novel compounds were revealed and it could be shown that the diversity of glycerol ether lipids in marine sediments is much higher than previously recognized. Among the studied lipids, isoprenoid GDGTs were shown as the most dominant component in all analyzed sediments with over 70% of total ether lipids. A comparison of the lipid composition of core and intact polar isoprenoid GDGTs pointed to a potential impact of live benthic archaea and their intact lipids on the application of the TEX86 SST proxy. The same study suggested that recycling of fossil GDGTs from planktonic archaea by the benthic archaeal community could be an important process. In a set of peat sediments, two intact polar lipids of the orphan branched GDGTs were for the first time observed. These branched GDGTs that constitute the BIT index have in their intact form glucuronosyl and glucosyl headgroups. The two compounds accounted for 4-7% of total IPLs, suggesting that their producers represent a sizeable but not dominant component of the microbial community. The identification of these intact polar precursors of these orphan lipids provides important constraints for the search of their microbial sources. The presence of newly identified glycerol ether lipids with distinctive structures and ubiquitous distribution in all analyzed marine sediments provided potential phylogenetic biomarkers and a large reservoir for novel molecular proxies to be developed. A series of novel ether core lipids coexisting with corresponding isoprenoid GDGTs was identified in all analyzed sediments. The first series of compounds,accounting on average for 7% of total ether lipids, was identified as glycerol dibiphytanol diethers (GDDs) and is considered to represent either biosynthetic intermediates or degradation products of GDGTs. A second series was identified as hydroxylated GDGTs based on nuclear magnetic resonance (NMR) and mass spectral interpretation. Accordingly, a series of unknown IPLs that had been previously reported as a major component in samples of archaeal cultures, sediments, and the water column were then recognized to be glycosidic hydroxy-GDGTs. The widespread occurrence of IPLs of hydroxy-GDGTs suggests an important contribution of specific archaeal species with high activity in a wide range of geological settings. Several other groups of novel compounds were also tentatively identified based on interpretation of mass spectra. Specifically, extended H-shaped GDGTs, hybrid isoprenoid/branched GDGTs, and overly and sparsely branched GDGTs are characterized with a common feature of methylation series, containing compounds with one -CH2- unit difference between each other. It is expected that the information encoded in the distribution of the novel lipids can be used to develop molecular proxies indicating past environmental factors such as temperature and salinity and/or information pertaining to the composition and activity of extant microbial communities. An overall distribution of detected glycerol ether lipids in marine subsurface sediments was shown by the estimated relative abundance of 11 structural groups, and therefore reflects a general composition of ether lipid producing microbes contributing to the sedimentary record.

Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.

We investigated microbial life preserved in a hydrothermally inactive silica–barite chimney in comparison with an active barite chimney and sediment from the Loki’s Castle low-temperature venting area at the Arctic Mid-Ocean Ridge (AMOR) using lipid biomarkers. Carbon and sulfur isotopes were used to constrain possible metabolic pathways. Multiple sulfur (δ34S, ∆33S) isotopes on barite over a cross section of the extinct chimney range between 21.1 and 22.5 ‰ in δ34S, and between 0.020 and 0.034 ‰ in Δ33S, indicating direct precipitation from seawater. Biomarker distributions within two discrete zones of this silica–barite chimney indicate a considerable difference in abundance and diversity of microorganisms from the chimney exterior to the interior. Lipids in the active and inactive chimney barite and sediment were dominated by a range of 13C-depleted unsaturated and branched fatty acids with δ13C values between −39.7 and −26.7 ‰, indicating the presence of sulfur-oxidizing and sulfate-reducing bacteria. The majority of lipids (99.5 %) in the extinct chimney interior that experienced high temperatures were of archaeal origin. Unusual glycerol monoalkyl glycerol tetraethers (GMGT) with 0–4 rings were the dominant compounds suggesting the presence of mainly (hyper-) thermophilic archaea. Isoprenoid hydrocarbons with δ13C values as low as −46 ‰ also indicated the presence of methanogens and possibly methanotrophs., Extremophiles, 18 (3)

We analyzed the abundance and distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in grain size fractions of 7 globally distributed river flank sediments and catchment soils in order to determine if and how the initial soil-brGDGT signature is influenced by hydrodynamic sorting upon entering a river and during subsequent transport from land to sea. BrGDGTs are hypothesized to form associations with high-surface-area fine-grained minerals in soils. Such associations, if maintained during transport, may impart resistance to degradation and promote downstream transport, reducing potential interferences by aquatic brGDGTs. We find that brGDGTs are indeed primarily associated with organic carbon (OC) bound to the clay-silt fraction (, Frontiers in Earth Science, 5, ISSN:2296-6463