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The Middle Miocene is characterized by a long‐term increase in the stable oxygen isotopic composition of benthic foraminifera (δ18Obenthic). However, it is unclear to what extent this increase reflects changes in seawater isotopic composition or deep water temperature. We present a high‐resolution alkenone hydrogen isotope (δ2HC37) record of the Middle Miocene from a core taken at the upper slope edge (about 409 m water depth) of the Porcupine Basin continental margin in the eastern North Atlantic Ocean, Site U1318 of the Integrated Ocean Drilling Program. The δ2HC37values vary between −174 and −200‰ with an average of −191 ± 5‰, similar to modern open‐ocean values. Importantly, they do not show a long‐term increase in surface seawater isotopes (δ2HSSW) during the Middle Miocene Climate Transition. Indeed, when δ18Obenthicis corrected for subsurface temperature, the bottom seawater oxygen isotopes (δ18OBSW) show no significant increase in this period. When the latter record is translated into the hydrogen isotopic composition of bottom seawater using the modern open‐ocean waterline, it has an average value of 5.8 ± 1.5‰, similar to the δ2HSSWof 5.2 ± 3.1‰ derived from δ2HC37:2,suggesting a relatively small difference between bottom and surface waters. Our results suggest a stable global surface seawater isotope evolution during the Middle Miocene, coupled with a long‐term decrease in bottom water temperature. No change in stable hydrogen isotopes of surface waters during the Middle Miocene Climate Transition period based on long chain alkenonesBottom seawater isotopes based on corrected oxygen isotopes of benthic foraminifera also show no long‐term change during the MMCTMiocene isotope events are reflected by only small δ18O and δ2H changes No change in stable hydrogen isotopes of surface waters during the Middle Miocene Climate Transition period based on long chain alkenones Bottom seawater isotopes based on corrected oxygen isotopes of benthic foraminifera also show no long‐term change during the MMCT Miocene isotope events are reflected by only small δ18O and δ2H changes

To assess the impacts of Amazon River discharge, Saharan dust deposition, N2‐fixation and mixed‐layer deepening on the biological carbon pump, sediment traps were moored from October 2012 to November 2013 at two sites in the western tropical North Atlantic (49°W,12°N/57°W,12°N). Particle exports interpreted along with satellite‐ and Argo‐float data show peak fluxes in biogenic silica (31 mg m−2d−1) and organic carbon (25 mg m−2d−1) during the fall of 2013 that were ten to five times higher than any time earlier during the year. These high export fluxes occurred in tandem with high surface chlorophyll aconcentrations associated with the dispersal of the Amazon River plume, following retroflection into the North‐Atlantic‐Counter‐Current. High fucoxanthin fluxes (> 80 μg m−2d−1) and low δ15N‐values (−0.6‰) suggest a large contribution by marine diatom‐diazotrophic‐associations, possibly enhanced by wet Saharan dust deposition. During summer, the Amazon River plume resulted in high mass fluxes at 57°W that were enriched in biogenic silica but weakly influenced by diazotrophic‐associations compared to the fall event at 49°W. High carbonate‐carbon fluxes (17 mg m−2d−1) dominated a second single event at 49°W during spring that was likely triggered by mixed‐layer deepening. Rain‐ratios of BSi/Ccarbamounted to 1.7 when associated with high export fluxes linked to the Amazon River plume. Compared to an annual average of 0.3, this indicates a more efficient uptake of CO2via the biological pump compared to when the plume was absent, hence supporting earlier observations that the Amazon River plume is important for ocean CO2sequestration.

In response to rising CO2concentrations and increasing global sea surface temperatures, oxygen minimum zones (OMZ), or “dead zones”, are expected to expand. OMZs are fueled by high primary productivity, resulting in enhanced biological oxygen demand at depth, subsequent oxygen depletion, and attenuation of remineralization. This results in the deposition of organic carbon‐rich sediments. Carbon drawdown is estimated by biogeochemical models; however, a major process is ignored: carbon fixation in the mid‐ and lower water column. Here, we show that chemoautotrophic carbon fixation is important in the Arabian Sea OMZ; and manifests in a 13C‐depleted signature of sedimentary organic carbon. We determined the δ13C values of Corgdeposited in close spatial proximity but over a steep bottom‐water oxygen gradient, and the δ13C composition of biomarkers of chemoautotrophic bacteria capable of anaerobic ammonia oxidation (anammox). Isotope mixing models show that detritus from anammox bacteria or other chemoautotrophs likely forms a substantial part of the organic matter deposited within the Arabian Sea OMZ (~17%), implying that the contribution of chemoautotrophs to settling organic matter is exported to the sediment. This has implications for the evaluation of past, and future, OMZs: biogeochemical models that operate on the assumption that all sinking organic matter is photosynthetically derived, without new addition of carbon, could significantly underestimate the extent of remineralization. Oxygen demand in oxygen minimum zones could thus be higher than projections suggest, leading to a more intense expansion of OMZs than expected. Oxygen minimum zones are areas in the ocean in which algae produce large amounts of organic material. When this sinks towards the seafloor, all oxygen at depth is used up. This results in vast “dead zones” where almost no oxygen is available to sustain life. With global warming, and increased nutrients from rivers, dead zones are forecast to expand. Computer models can calculate this, by considering algal production, and the amount of material delivered to the seafloor. However, these models often ignore a major process: anaerobic bacteria in the deeper water column, that can live at the edge or in the middle of these dead zones, which can also produce organic material from the dissolved CO2. In this study, we used the fact that these bacteria add a distinct signature to the organic material, to show that one fifth of the organic matter on the seafloor could stem from bacteria living in these dead zones. Thus, models that have missed out on considering this contribution could have underestimated the extent of oxygen depletion we are to expect in a future, warming world. A more intense expansion of dead zones than expected could have severe ecological, economical (fisheries), and climatic consequences. One fifth of organic matter on Arabian Sea seafloor could stem from bacterial carbon fixation in the oxygen minimum zoneEvaluation of past anoxic events needs to take chemoautotrophic contribution into account in isotope balancesBiogeochemical models ignoring dark carbon fixation could highly underestimate oxygen demand and thus expansion of oxygen minimum zones

The Eocene – Oligocene Transition (EOT, ~34–33.5 Ma) marks a major transition in Cenozoic climate evolution through the relatively rapid establishment of a continental-scale ice sheet on Antarctica. The EOT is characterized by two ~200 kyr spaced shifts (termed EOT-1 and Oi-1) in the oxygen isotopic composition (d18O) of benthic foraminifera, representing both changes in continental ice-volume and temperature. Estimates of the timing and magnitude of these changes during this critical phase in Earth’s climatic evolution are controversial. Here we present marine palynological assemblage data, in particular of organic-walled dinoflagellate cysts (dinocysts), across a classic upper Eocene to lower Oligocene neritic succession cored in Alabama, USA; the Saint Stephens Quarry (SSQ) borehole. These palynological data combined with lithological information allow the identification of three sequence boundaries across the EOT. Critically, we identify a sequence boundary at the level corresponding to the EOT-1. Integrated sea level and paleotemperature records show that EOT-1 primarily represents cooling with some minor and transient continental ice sheet expansion. Furthermore, we identify a significant hiatus, likely caused by major sea level fall at the base of Magnetochron C13n that corresponds to the Oi-1 shift. This clarifies the d18O records from SSQ that essentially lack the expected pronounced shift to positive d18O values so characteristic for Oi-1. Furthermore, we document originations and extinctions of potentially temperature-sensitive dinocysts associated with the EOT-1. In contrast, the Oi-1 does not stand out as period of substantial dinoflagellate turnover. The combined results illustrate that major cooling, limited and transient ice growth and major biotic change were occurring before the full-size expansion of the Antarctic cryosphere.

Biomass burning on the African continent is widespread, and interactions with climate, vegetation dynamics, and biogeochemical cycling are complex. To obtain a better understanding of these complex relationships, African fire history has been widely studied, although mostly on relatively short timescales (i.e., years to kiloyears) and less commonly on long‐term scales. Here we present a 192‐kyr, continuous biomass‐burning record from sub‐Saharan Northwest Africa based on the fire biomarker levoglucosan in a marine sediment core offshore Guinea. Notable features of our record include an increase in levoglucosan accumulation at 80 ka and two peaks at 50–60 ka. The event at 80 ka is likely related to an overall increase in sedimentation rates rather than an increase in biomass burning in the Northwest African savanna region. Our record indicates that glacial/interglacial changes in regional climate and vegetation composition (C3vs. C4plants) were not a major influence on biomass burning over the last 192 kyr. However, we suggest that the burning events at 50–60 ka might be caused by increased occurrence of C3vegetation and human settlement in this region. At this time, the savanna region became wetter and fuel loads likely increased. Therefore, the region was more hospitable for humans, who likely used fire for hunting activities. Collectively, we hypothesize that on longer (glacial/interglacial) timescales, biomass burning, regional climate, and African vegetation are not necessarily coupled, while around 50–60 ka, higher fuel loads and human fire use may have influenced fire occurrence in sub‐Saharan Northwest Africa. Biomass burning history of sub‐Saharan Northwest Africa during the last 192 kyr was studied, based on levoglucosan accumulation ratesGlacial/interglacial changes in regional climate and vegetation composition were not a major influence on biomass burningFire events around 50–60 ka in sub‐Saharan Northwest Africa might be caused by increased fuel loads and human fire use

Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO2concentrations are crucial for developing better projections of future climate change. Deep-ocean1,2and high-latitude3palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data4–6to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing7,8, rather than changes in ocean circulation9,10, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO2reconstructions8yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates11. A 26-million-year record of equatorial sea surface temperatures reveals synchronous changes of tropical and polar temperatures during the Eocene epoch forced by variations in concentrations of atmospheric carbon dioxide, with a constant degree of polar amplification.

The long‐chain diol index (LDI) is a new organic sea surface temperature (SST) proxy based on the distribution of long‐chain diols. It has been applied in several environments but not yet in subpolar regions. Here we tested the LDI on surface sediments and a sediment core from the Sea of Okhotsk, which is the southernmost seasonal sea ice‐covered region in the Northern Hemisphere, and compared it with other organic temperature proxies, that is, U37k′and TEXL86. In the surface sediments, the LDI is correlated with autumn SST, similar to the U37k′but different from the TEXL86that correlates best with summer sea subsurface temperature. Remarkably, the obtained local LDI calibration was significantly different from the global core‐top calibration. We used the local LDI calibration to reconstruct past SST changes in the central Sea of Okhotsk. The LDI‐SST record shows low glacial (Marine Isotope Stage, MIS 2, 4, and 6) and high interglacial (MIS 1 and MIS 5) temperatures and follows the same pattern as the U37k′‐SST and a previously published TEXL86temperature record. Similar to the modern situation, the reconstructed temperatures during the interglacials likely reflect different seasons, that is, summer for the TEXL86and autumn for U37k′and LDI. During glacials, the reconstructed temperatures of all three proxies are similar to each other, likely reflecting summer temperatures as this was the only season free of sea ice. Our results suggest that the LDI is a suitable proxy to reconstruct subpolar seawater temperatures. This study discusses the lipid‐based sea temperature reconstructions of the central Sea of OkhotskThe LDI reflects autumn sea surface temperature in core topsDuring glacial stages Uk′37, TEXL86, and LDI reflect summer sea temperature

The TEX86paleothermometer has been extensively used to reconstruct past sea water temperatures, but it remains unclear which export depths the proxy represents. Here we used a novel approach to better constrain the proxy recording depths by investigating paleotemperature proxies (TEX86, U37K′${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$, RI−OH and RI−OH′) from two pairs of proximal (<12 km apart) cores from Chilean and Angola margins, respectively. These cores are from steep continental slopes and lower shelves, which leads to a substantial difference in water depth between them despite being closely located. Surprisingly, the deep and the shallow U37K′${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$records at the Chilean margin show dissimilarities, in contrast to the similar records from the Angola margin, which may be due to post‐depositional alteration at the former sites. In contrast, the TEX86records were statistically indistinguishable between the sites at both the locations, even though the GDGT [2]/[3] ratio suggests GDGTs derived from potentially different archaeal communities residing at different depths. A short‐lived difference between the TEX86records is observed during the last glacial period at the Angola margin, possibly due to a contribution of Antarctic Intermediate Waters to the deep site. Modelling suggests that the TEX86source signal at our core sites reaches its peak abundance at water depths shallower than 350 m. The RI−OH and RI−OH′ records show similar variability as the TEX86records, although regional differences in their absolute temperature estimates exist. Our approach using proximal sediment cores at steep slopes appears useful to constrain the export depth of organic proxy signals for paleo‐reconstructions. Source signal of TEX86proxy is likely derived from depths shallower than 350 m at Chilean and Angola marginsOH‐GDGT based proxies show similar variability as TEX86records, but show regional differences in their absolute temperature estimatesU37K′${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$proxy signal may be impacted by post‐depositional changes or lateral transport even for closely located cores Source signal of TEX86proxy is likely derived from depths shallower than 350 m at Chilean and Angola margins OH‐GDGT based proxies show similar variability as TEX86records, but show regional differences in their absolute temperature estimates U37K′${\mathrm{U}}_{37}^{{\mathrm{K}}^{\prime }}$proxy signal may be impacted by post‐depositional changes or lateral transport even for closely located cores

The increasing production of nitrogen-containing fertilizers is crucial to meet the global food demand, yet high losses of reactive nitrogen associated with the food production/consumption chain progressively deteriorate the natural environment. Currently, mesophilic nitrogen-removing microbes eliminate nitrogen from wastewaters. Although thermophilic nitrifiers have been separately enriched from natural environments, no bioreactors are described that couple these processes for the treatment of nitrogen in hot wastewaters. Samples from composting facilities were used as inoculum for the batch-wise enrichment of thermophilic nitrifiers (350 days). Subsequently, the enrichments were transferred to a bioreactor to obtain a stable, high-rate nitrifying process (560 days). The community contained up to 17% ammonia-oxidizing archaea (AOAs) closely related to ‘CandidatusNitrososphaera gargensis’, and 25% nitrite-oxidizing bacteria (NOBs) related to Nitrospira calida. Incorporation of 13C-derived bicarbonate into the respective characteristic membrane lipids during nitrification supported their activity as autotrophs. Specific activities up to 198±10 and 894±81?mg?N?g-1VSS per day for AOAs and NOBs were measured, where NOBs were 33% more sensitive to free ammonia. The NOBs were extremely sensitive to free nitrous acid, whereas the AOAs could only be inhibited by high nitrite concentrations, independent of the free nitrous acid concentration. The observed difference in product/substrate inhibition could facilitate the development of NOB inhibition strategies to achieve more cost-effective processes such as deammonification. This study describes the enrichment of autotrophic thermophilic nitrifiers from a nutrient-rich environment and the successful operation of a thermophilic nitrifying bioreactor for the first time, facilitating opportunities for thermophilic nitrogen removal biotechnology.

The increasing production of nitrogen-containing fertilizers is crucial to meet the global food demand, yet high losses of reactive nitrogen associated with the food production/consumption chain progressively deteriorate the natural environment. Currently, mesophilic nitrogen-removing microbes eliminate nitrogen from wastewaters. Although thermophilic nitrifiers have been separately enriched from natural environments, no bioreactors are described that couple these processes for the treatment of nitrogen in hot wastewaters. Samples from composting facilities were used as inoculum for the batch-wise enrichment of thermophilic nitrifiers (350 days). Subsequently, the enrichments were transferred to a bioreactor to obtain a stable, high-rate nitrifying process (560 days). The community contained up to 17% ammonia-oxidizing archaea (AOAs) closely related to ‘Candidatus Nitrososphaera gargensis’, and 25% nitrite-oxidizing bacteria (NOBs) related to Nitrospira calida. Incorporation of 13C-derived bicarbonate into the respective characteristic membrane lipids during nitrification supported their activity as autotrophs. Specific activities up to 198±10 and 894±81 mg N g−1VSS per day for AOAs and NOBs were measured, where NOBs were 33% more sensitive to free ammonia. The NOBs were extremely sensitive to free nitrous acid, whereas the AOAs could only be inhibited by high nitrite concentrations, independent of the free nitrous acid concentration. The observed difference in product/substrate inhibition could facilitate the development of NOB inhibition strategies to achieve more cost-effective processes such as deammonification. This study describes the enrichment of autotrophic thermophilic nitrifiers from a nutrient-rich environment and the successful operation of a thermophilic nitrifying bioreactor for the first time, facilitating opportunities for thermophilic nitrogen removal biotechnology.

A substantial extinction of megafauna occurred in Australia between 50 and 45 kyr ago, a period that coincides with human colonization of Australia. Large shifts in vegetation also occurred around this time, but it is unclear whether the vegetation changes were driven by the human use of fire—and thus contributed to the extinction event—or were a consequence of the loss of megafaunal grazers. Here we reconstruct past vegetation changes in southeastern Australia using the stable carbon isotopic composition of higher plant wax n-alkanes and levels of biomass burning from the accumulation rates of the biomarker levoglucosan from a well-dated sediment core offshore from the Murray–Darling Basin. We find that from 58 to 44?kyr ago, the abundance of plants with the C4carbon fixation pathway was generally high—between 60 and 70%. By 43?kyr ago, the abundance of C4plants dropped to 30% and biomass burning increased. This transient shift lasted for about 3,000 years and came after the period of human arrival and directly followed megafauna extinction at 48.9–43.6?kyr ago. We conclude that the vegetation shift was not the cause of the megafaunal extinction in this region. Instead, our data are consistent with the hypothesis that vegetation change was the consequence of the extinction of large browsers and led to the build-up of fire-prone vegetation in the Australian landscape.

Diatoms are one of the most important organisms contributing to aquatic primary productivity and their sterols are frequently used as markers for their presence and abundance. In this study, the sterol composition of >100 diatom cultures was analyzed and its distribution was compared to the diatom phylogeny to identify typical diatom biomarkers. Forty‐four sterols were detected, 11 of them being commonly present as major sterols (contributing >10% to the total sterols). 24‐Methylcholesta‐5,24(28)‐dien‐3β‐ol is the most common sterol in diatoms, being present in 67% of all cultures analyzed, followed by the Δ5sterols, cholest‐5‐en‐3β‐ol (cholesterol), 24‐methylcholest‐5‐en‐3β‐ol, and 24‐ethylcholest‐5‐en‐3β‐ol. 24‐Methylcholesta‐5,22E‐dien‐3β‐ol, previously suggested to be specific for diatoms, was only the fifth most common sterol; this sterol was absent in some of the major diatom groups, and high relative concentrations seem to be restricted to pennate diatoms. No sterols are restricted to specific phylogenetic groups of diatoms. Cluster analyses, however, do reveal distinct sterol distributions: Thalassiosirales typically contain high relative abundances of 24‐methylcholesta‐5,24(28)‐dien‐3β‐ol, high relative abundances of cholesta‐5,22E‐dien‐3β‐ol are typical for Cymatosirales, high relative abundances of 24‐ethylcholesta‐5,22E‐dien‐3β‐ol are characteristic for related Amphora, Amphiprora, and Entomoneisspecies, and a combination of high relative abundances of 24‐methylcholest‐5‐en‐3β‐ol, 24‐methylcholesta‐5,24(28)‐dien‐3β‐ol, and 24‐ethylcholest‐5‐en‐3β‐ol is typical for Attheyaspecies. High contributions of 24‐methylcholesta‐5,22E‐dien‐3β‐ol (>50% of all sterols) seem to be restricted to pennate diatoms. None of the major sterols found in diatoms can be used as an unambiguous diatom biomarker because all of them have been reported as common sterols in other algal groups.

The presence and abundance of anaerobic ammonium‐oxidizing (anammox) bacteria was investigated in continental shelf and slope sediments (300‐3000 m water depth) off northwest Africa in a combined approach applying quantitative polymerase chain reaction (q‐PCR) analysis of anammox‐specific 16S rRNA genes and anammox‐specific ladderane biomarker lipids. We used the presence of an intact ladderane monoether lipid with a phosphocholine (PC) headgroup as a direct indicator for living anammox bacteria and compared it with the abundance of ladderane core lipids derived from both living and dead bacterial biomass. All investigated sediments contained ladderane lipids, both intact and core lipids, in agreement with the presence of anammoxspecific 16S rRNA gene copies, indicating that anammox occurs at all sites. Concentrations of ladderane core lipids in core top sediments varied between 0.3 and 97 ng g−1sediment, with the highest concentrations detected at the sites located on the shelf at shallower water depths between 300 and 500 m. In contrast, the C20[3]‐ ladderane monoether‐PC lipid was most abundant in a core top sediment from 1500 m water depth. Both anammox‐specific 16S rRNA gene copy numbers and the concentration of the C20[3]‐ladderane monoether‐PC lipid increased downcore in sediments located at greater water depths, showing highest concentrations of 1.2 × 108copies g−1sediment and 30 pg g−1sediment, respectively, at the deepest station of 3000 m water depth. This suggests that the relative abundance of anammox bacteria is higher in sediments at intermediate to deep water depths where carbon mineralization rates are lower but where anammox is probably more important than denitrification.

The basic structure and stereochemistry of the characteristic glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipid of cosmopolitan pelagic crenarchaeota has been identified by high field two-dimensional (2D)-NMR techniques. It contains one cyclohexane and four cyclopentane rings formed by internal cyclisation of the biphytanyl chains. Its structure is similar to that of GDGTs biosynthesized by (hyper)thermophilic crenarchaeota apart from the cyclohexane ring. These findings are consistent with the close phylogenetic relationship of (hyper)thermophilic and pelagic crenarchaeota based 16S rRNA. The latter group inherited the biosynthetic capabilities for a membrane composed of cyclopentane ring-containing GDGTs from the (hyper)thermophilic crenarchaeota. However, to cope with the much lower temperature of the ocean, a small but key step in their evolution was the adjustment of the membrane fluidity by making a kink in one of the bicyclic biphytanyl chains by the formation of a cyclohexane ring. This prevents the dense packing characteristic for the cyclopentane ring-containing GDGTs membrane lipids used by hyperthermophilic crenarchaeota to adjust their membrane fluidity to high temperatures.

Monosaccharides were derivatized using methylboronic acid and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), and the δ¹³C values of these derivatives measured by gas chromatography/combustion/isotope-ratio-monitoring mass spectrometry to determine the original ¹³C-content of the monosaccharides. Comparison with the measured off-line δ¹³ values of the monosaccharides shows that no fractionation in ¹³C takes place during derivatization. The methylboronic derivatization method has proven to be a new method for natural abundance isotopic analysis of intact monosaccharides (arabinose, xylose, fucose, fructose and glucose). The method is rapid, does not involve isotopic fractionation during derivatization, and gives more precise δ¹³C values than other methods reported. The method was successfully applied to determine the δ¹³C value of glucose of the freshwater alga Scenedesmus communis. Copyright © 2001 John Wiley & Sons, Ltd.

Monosaccharides were derivatized using methylboronic acid and N,O‐bis(trimethylsilyl)trifluoroacetamide (BSTFA), and the δ13C values of these derivatives measured by gas chromatography/combustion/isotope‐ratio‐monitoring mass spectrometry to determine the original 13C‐content of the monosaccharides. Comparison with the measured off‐line δ13values of the monosaccharides shows that no fractionation in 13C takes place during derivatization. The methylboronic derivatization method has proven to be a new method for natural abundance isotopic analysis of intact monosaccharides (arabinose, xylose, fucose, fructose and glucose). The method is rapid, does not involve isotopic fractionation during derivatization, and gives more precise δ13C values than other methods reported. The method was successfully applied to determine the δ13C value of glucose of the freshwater alga Scenedesmus communis. Copyright © 2001 John Wiley & Sons, Ltd.

To assess the effects related to known and proposed biosynthetic pathways on the 13C content of lipids and storage products of the photoautotrophic bacteriumChloroflexus aurantiacus, the isotopic compositions of bulk cell material, alkyl and isoprenoid lipids, and storage products such as glycogen and polyhydroxyalkanoic acids have been investigated. The bulk cell material was 13‰ depleted in 13C relative to the dissolved inorganic carbon. Evidently, inorganic carbon fixation by the main carboxylating enzymes used by C. aurantiacus, which are assumed to use bicarbonate rather than CO2, results in a relatively small carbon isotopic fractionation compared with CO2fixation by the Calvin cycle. Even carbon numbered fatty acids, odd carbon numbered fatty acids, and isoprenoid lipids were 14, 15, and 17–18‰ depleted in 13C relative to the carbon source, respectively. Based on the 13C contents of alkyl and isoprenoid lipids, a 40‰ difference in 13C content between the carboxyl and methyl carbon from acetyl-coenzyme A has been calculated. Both sugars and polyhydroxyalkanoic acid were enriched in 13C relative to the alkyl and isoprenoid lipids. To the best of our knowledge this is the first report in which the stable carbon isotopic composition of a large range of biosynthetic products in a photoautotrophic organism has been investigated and interpreted based on previously proposed inorganic carbon fixation and biosynthetic pathways. Our results indicate that compound-specific stable carbon isotope analysis may provide a rapid screening tool for carbon fixation pathways.

The stable carbon isotopic compositions of the inorganic carbon source, bulk cell material, and isoprenoid lipids of the hyperthermophilic crenarchaeon Metallosphaera sedula, which uses a 3‐hydroxypropionate‐like pathway for autotrophic carbon fixation, have been measured. Bulk cell material was approximately 3‰ enriched in 13C relative to the dissolved inorganic carbon, and 2‰ depleted in 13C relative to isoprenoid membrane lipids. The isotope data suggested that M. sedulauses mainly bicarbonate rather than CO2as inorganic carbon source, which is in accordance with a 3‐hydroxypropionate‐like carbon fixation pathway. To the best of our knowledge this is the first report of 13C fractionation effects of such a hyperthermophilic crenarchaeon.

Stable carbon isotopic analysis was performed on sedimentary biomarkers of a shallow sulfide-rich monomictic lake, Lake Cisó (NE Spain). Specific biomarkers derived from phototrophic sulfur bacteria in Lake Cisó were considerably depleted in 13C, most likely due to the depleted 13C-content of the dissolved inorganic carbon that was photosynthetically fixed. Recycling of respired CO2, a well-known phenomenon in monomictic lakes, probably caused this depletion. The stable carbon isotopic composition of terrestrial markers, such as C25–33odd-carbon-numbered n-alkanes and C22–30even-carbon-numbered n-alkan-1-ols and fatty acids, were rather similar to each other and their 13C depleted values (c. −31 to −35‰) indicated that they were derived from the surrounding vegetation. Phytol was predominantly derived from the bacteriochlorophylls of phototrophic purple sulfur bacteria as were specific fatty acids.

The distribution of apolar and polar lipids and their stable carbon isotopic compositions were determined for a number of sediment samples from different sites in the Arabian Sea. Lipids are mainly derived from planktonic Archaea and a range of algae, including Haptophytes, Eustigmatophytes and diatoms. The stable carbon isotopic compositions of compounds from diatoms, highly branched isoprenoids, fall into distinct groups suggesting other sources beside the diatom species Rhizosolenia setigerafor these compounds. High amounts of sterol ethers, which may be derived from diatoms, were also detected. A recently identified triterpenoid, malabaricatriene, was also present in high abundance in these samples. The terrestrial input of lipids consists of n-alkanes and their carbon isotopic compositions show that they are derived from aeolian dust input from the Arabian Peninsula. The isotopic compositions of C37alkenones from two cores during the last 15 ka is relatively constant and suggests that growth conditions for Haptophyte algae (averaged over 500 years) did not change significantly over this period.

A method combining normal phase high performance liquid chromatography (HPLC) with positive ion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was developed for the analysis of intact glycerol dialkyl glycerol tetraethers (GDGTs) in archaeal cell material and sediments. All GDGTs previously reported to occur in the thermophilic archaeon Sulfolobus solfataricus could be identified based on their mass spectra and retention time. Positive ion mass spectra consisted of abundant protonated molecules and fragment ions corresponding to loss of water and the glycerol moiety. In addition, two novel GDGTs representing alternative combinations of biphytanyl moieties were observed. Using this method, the tetraethers present in the thermophilic archaeon Metallosphaera sedula and two sediment samples were characterized. This rapid method will greatly contribute to the establishment of the sedimentary record of these compounds and increase our understanding of archaea and their occurrence in widely different environments. Copyright © 2000 John Wiley & Sons, Ltd.

A method combining normal phase high performance liquid chromatography (HPLC) with positive ion atmospheric pressure chemical ionization mass spectrometry (APCI‐MS) was developed for the analysis of intact glycerol dialkyl glycerol tetraethers (GDGTs) in archaeal cell material and sediments. All GDGTs previously reported to occur in the thermophilic archaeon Sulfolobus solfataricuscould be identified based on their mass spectra and retention time. Positive ion mass spectra consisted of abundant protonated molecules and fragment ions corresponding to loss of water and the glycerol moiety. In addition, two novel GDGTs representing alternative combinations of biphytanyl moieties were observed. Using this method, the tetraethers present in the thermophilic archaeon Metallosphaera sedulaand two sediment samples were characterized. This rapid method will greatly contribute to the establishment of the sedimentary record of these compounds and increase our understanding of archaea and their occurrence in widely different environments. Copyright © 2000 John Wiley & Sons, Ltd.

We present a high‐resolution multiproxy middle Miocene sea surface temperature (SST) and productivity (SSP) reconstruction of Integrated Ocean Drilling Program Site U1318, from the upper slope edge (∼400 m water depth) of the Porcupine Basin continental margin, eastern North Atlantic Ocean. Biomarker and dinoflagellate cyst proxies reveal warm and mostly stratified waters during the Miocene Climatic Optimum (MCO) that cooled ∼3°C across the Miocene Climate Transition (MCT). The organic biomarker (TEX86and UK′37) paleothermometers document a series of 11 transient cooling events (CEs), superimposed on the long‐term climate evolution. These CEs are associated with increases in cold‐water dinocysts and correlate to global benthic δ18O shifts, including the Mi‐2, Mi‐3, and Mi‐4 events. Most CEs are also associated with increases in primary productivity. A prolonged interval of high SSP between ∼13.8 and 13.6 Ma supports the idea that carbon production (and burial) in shallow areas represents a feedback mechanism contributing to long‐term atmospheric CO2decline and cooling during the MCT. SST comparison in three North Atlantic sites (Azores Site 608, Porcupine Basin Site U1318, and Rockall Plateau Site 982) reveals that MCO SSTs are much warmer at Site 608 than at the other two sites. The low‐resolution SST record of Site 982 shows no decrease in temperature around the MCT. This may be linked to contemporaneous tectonic changes in the Tethys, Central American, and Arctic Seaways impacting local ocean circulation, superimposed on global drivers of climate change. The middle Miocene record of Site U1318 reveals mean annual SSTs ∼10°C warmer than at present and registers 11 coolingsSeveral of these cooling events are associated with increases in sea surface productivity (SSP)SSP and carbon burial on continental shelves may be key to explain the disruptions in the global carbon cycle during the middle Miocene The middle Miocene record of Site U1318 reveals mean annual SSTs ∼10°C warmer than at present and registers 11 coolings Several of these cooling events are associated with increases in sea surface productivity (SSP) SSP and carbon burial on continental shelves may be key to explain the disruptions in the global carbon cycle during the middle Miocene

The Huqf oil from Oman and other time-equivalent oils are characterized by relatively large contents of mid-chain branched monomethyl alkanes. The Huqf oil, the saturated hydrocarbon fractions, the desulfurized polar fractions of the bitumens and the kerogen pyrolysates of three potential source rocks from the Huqf Formation (Oman) were analyzed in order to resolve the origin of these mid-chain branched monomethyl alkanes. Using off-line pyrolysis and chemical degradation in combination with compound specific carbon isotope analysis, it was assessed that the mid-chain branched monomethyl alkanes are not rearrangement products but are derived from a biological source, probably from lipids with C28+carbon skeletons and methyl branching at the 12- or 13-position. These compounds were incorporated in the kerogen through reactions of sulfur with functional groups at different positions in the precursor lipid(s).

Abstract.: The unicellular green alga Chlamydomonas monoica Strehlow is known to produce zygospores with a cell wall that is resistant against microbial and chemical attack. This resistance is thought to be due to the presence of a sporopollenin-like material. However, the resistant nature of sporopollenin-like materials seriously hampers their structural analysis. With complementary techniques such as 13C-nuclear magnetic resonance spectroscopy, Curie-point pyrolysis-gas chromatography/mass spectroscopy and RuO4 chemical degradation, the chemical composition of resistant biopolymer in the isolated cell walls of C. monoica zygospores was determined. This material is composed of C22–C30 linear alcohols and carboxylic acids, intermolecularly linked via ester and ether-linkages similar to the resistant aliphatic biopolymers encountered in the walls of the vegetative cells of the algae Tetraedron minimum, Scenedesmus communis and Pediastrum boryanum.

All trans2,6,10,15,19-pentamethylicosa-2,6,14,18-tetraene 1 has been isolated from the methanogenic archaeon Methanosarcina mazeiand identified by 1H and 13C NMR spectroscopy and mass spectrometry.

A novel aromatised 8(14)-secohopanoid 1(C 31H 42) possessing a fluorene moiety, formed from derivatives of bacteriohopanepolyols by cyclisation, aromatisation, ring opening and side-chain cleavage reactions during sediment diagenesis, has been isolated from a 150 Ma old marine sedimentary rock and identified by 1H and 13C NMR spectroscopy and mass spectrometry.

Homologous series (C15-C24) of novel 3-n-alkyl-1,2-dithianes and 3-n-alkyl-6-methyl-1,2-di-thianes have been identified in immature sediments. The identification of these compounds was based on comparison of mass spectra and Chromatographie data with those of synthesized 3-methyl-6-tridecyll, 2-dithiane. In addition, 4-methyl-3-(3,7,11-trimethyldodecyl)-1,2-dithiane, 4-(4,8,12-trimethyltridecyl)-1,2-dithiane, 5-methyl-4-(3,7,11-trimethyldodecyl)-1,2,3-trithiepane, and a 1,2-dithiane possessing a pentakishomohopane carbon skeleton were tentatively assigned on the basis of mass spectral characteristics, selective chemolysis, and desulphurisation. The occurrence of these cyclic di-and trisulphides with linear, acyclic isoprenoid and hopanoid carbon skeletons in thermally immature sediments indicates that inorganic polysulphides are incorporated into functionalised lipids during the early stages of diagenesis.

In a North Sea oil, the carotenoid derivatives β-carotene, β-isorenieratane, and isorenieratane were identified, together with a series of aryl isoprenoids with a 2,3,6-trimethyl substitution pattern for the aromatic ring. The δ13C values of β-carotene and β-isorenieratane are similar, whereas isorenieratane is ca. 15% heavier. This suggests that β-isorenieratane is not derived from β-isorenieratane biosynthesised by Chlorobiaceae, but from aromatisation of β-carotene. This was confirmed by laboratory aromatisation of partially hydrogenated β-carotene, which yielded β-isorenieratane as the main product. The aryl isoprenoids, which can be formed by CC bond cleavage of both isorenieratane and β-isorenieratane, have a mixed isotopic signature in the oil. These results indicate that mere identification of aryl isoprenoids, without determination of their δ13C values, cannot be used to assess the presence of Chlorobiaceae, and, thus, photic zone anoxia in the depositional environment.

The 300 m section of the Miocene Monterey Formation outcropping at Shell Beach (Pismo basin; ca. 15-11 Ma) is composed of calcareous phosphatic (15.1–14.5 Ma) and siliceous facies (14.5–11.0 Ma). An objective of this paper is to document lateral paleoenvironmental changes in the Miocene Moneterey Formation by comparing the Shell Beach (SB) profile with the Naples Beach (NB) section in the Santa Barbara-Ventura basin (Schouten et al., 1997) which is ∼80 km to the south. Eight samples (one sample representing, on average, a time period of ca. 2000 y) from this section were analyzed for variations of extractable biomarkers and their carbon isotopic signatures as indicators for paleoenvironmental change during the Miocene. Saturated hydrocarbons present include 28,30-dinorhopane, phytane, n-alkanes (C17C31), lycopane, and 17β,21β(H)-homohopane. The biomarkers released after desulfurization of the polar fractions predominantly consist of phytane, 2,6,10,14-tetramethyl-7-(3-methylpentyl)pentadecane, C17C31n-alkanes, regular 5α- and 5β-steranes, dinosteranes, and (22R)-17β,21β(H)-pentakishomohopane. Steranes have similar carbon isotopic compositions (−25 to −27‰) throughout the section and are isotopically similar at both sites, indicating laterally similar and vertically stable environmental conditions for algae living in the upper part of the photic zone. Free and S-bound n-alkanes at SB mainly originate from marine organisms and not from terrestrial sources as in the NB section. S-bound pentakishomohopane is ca. 1–4‰ depleted compared to the steranes and is thought to be derived from the deeper water dwelling cyanobacteria. These findings are consistent with stable carbon isotopic data obtained for these compounds from Middle Miocene Monterey sediments at Naples Beach and indicates similar environmental conditions in the depositional environments of the Santa Barbara-Ventura and the Pismo basin. S-bound highly branched isoprenoids have, at both sites, different isotopic compositions indicating the presence of different diatom species, special growth conditions, or different bloom periods in the Pismo basin. The carbon isotopic composition of 28,30-dinorhopane shifts to more depleted values up section, suggesting that the dinorhopane-synthesizing organism or organisms live on CO2, which is isotopically influenced by methane production and oxidation. The C31 hopane is enriched by 1–4‰ in 13C compared to other hopanes and steranes. Specific bacteria, possibly heterotrophs, may have been the organisms producing this compound.

A wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene, a pigment of the photosynthetic green sulphur bacteria Chlorobiaceae, has been identified in a number of sedimentary rocks ranging from Ordovician to Miocene. Compound identification is based on NMR, mass spectrometry, the presence of atropisomers, and stable carbon isotopes. Atropisomers contain an axially chiral centre which, in combination with other chiral centres, results in two or more diastereomers that can be separated on a normal GC column. Chlorobiaceaeuse the reverse TCA cycle to fix carbon, so that their biomass is enriched in 13C. High 13C contents of isorenieratene derivatives therefore support their inferred origins.

Several studies indicate that North Atlantic Deep Water (NADW) formation might have initiated during the globally warm Eocene (56–34 Ma). However, constraints on Eocene surface ocean conditions in source regions presently conducive to deep water formation are sparse. Here we test whether ocean conditions of the middle Eocene Labrador Sea might have allowed for deep water formation by applying (organic) geochemical and palynological techniques, on sediments from Ocean Drilling Program (ODP) Site 647. We reconstruct a long‐term sea surface temperature (SST) drop from ~30°C to ~27°C between 41.5 to 38.5 Ma, based on TEX86. Superimposed on this trend, we record ~2°C warming in SST associated with the Middle Eocene Climatic Optimum (MECO; ~40 Ma), which is the northernmost MECO record as yet, and another, likely regional, warming phase at ~41.1 Ma, associated with low‐latitude planktic foraminifera and dinoflagellate cyst incursions. Dinoflagellate cyst assemblages together with planktonic foraminiferal stable oxygen isotope ratios overall indicate low surface water salinities and strong stratification. Benthic foraminifer stable carbon and oxygen isotope ratios differ from global deep ocean values by 1–2‰ and 2–4‰, respectively, indicating geographic basin isolation. Our multiproxy reconstructions depict a consistent picture of relatively warm and fresh but also highly variable surface ocean conditions in the middle Eocene Labrador Sea. These conditions were unlikely conducive to deep water formation. This implies either NADW did not yet form during the middle Eocene or it formed in a different source region and subsequently bypassed the southern Labrador Sea. The middle Eocene Labrador Sea was characterised by warm, low‐salinity surface watersWe find two phases of superimposed sea surface warming and subtropical plankton incursions, including the Middle Eocene Climatic OptimumBottom water stable carbon and oxygen isotope ratios indicate isolated basin

Modern biogeochemical conditions of the Eastern Equatorial Pacific (EEP) region are characterized by high macronutrient concentrations but low phytoplankton abundance due to both iron and silicic acid limitation. Since primary producers significantly impact the global carbon cycle, paleoproductivity in relation to climate change and nutrient availability in this region has been a topic of a number of studies. However, the complex dynamics of this region, especially east of the Galapagos Islands, has led to some discrepancies when linking reconstructed paleoproductivity with potential mechanisms for higher primary productivity. Here we focus on reconstructing primary productivity of haptophyte algae and diatoms, as well as continental material input, sea surface salinity, and sea surface temperature, and compare these reconstructions with existing records for the period comprised between 150 and 110 ka (the penultimate deglaciation period) with the aim to understand the mechanisms that most significantly influence phytoplankton growth over the EEP region east of the Galapagos Islands. Our results suggest enhanced upwelling in the EEP system during the penultimate deglaciation and increased phytoplankton abundance mainly as the result of both the increasing influence of nutrient‐rich Southern Ocean sourced waters through the Equatorial Undercurrent and a higher input of iron through atmospheric deposition. The highest phytoplankton abundances recorded at the study site during the penultimate deglaciation also suggest that maximum input of nutrients might have occurred during the millennial‐scale event Heinrich Event 11 in the North Atlantic as a result of global atmospheric and oceanic reorganizations. Primary productivity in the Eastern Equatorial Pacific, east of the Galapagos Islands, increased during the penultimate deglaciationThe supply of limiting nutrients via the Equatorial Undercurrent and atmospheric depositions were key to enhance primary productivityGlobal changes occurring during Heinrich Event 11 favored the arrival of nutrients to the easternmost region of the Equatorial Pacific

A suite of six sterols, lanosterol, lanost‐8(9)‐en‐3β‐ol, 4,4‐dimethylcholesta‐8(14),24‐dien‐3β‐ol, 4,4‐dimethylcholest‐8(14)‐en‐3β‐ol, 4‐methylcholesta‐8(14),24‐dien‐3β‐ol and 4‐methylcholest‐8(14)‐en‐3β‐ol, were identified in the psychrophilic methanotrophic bacterium, Methylosphaera hansonii. Their presence suggests that the capacity for sterol biosynthesis in methanotrophic bacteria is limited to the family Methylococcaceaebut which have widely different optimal growth temperatures.

Paleoceanographical studies of Marine Isotope Stage (MIS) 11 have revealed higher‐than‐present sea surface temperatures (SSTs) in the North Atlantic and in parts of the Arctic but lower‐than‐present SSTs in the Nordic Seas, the main throughflow area of warm water into the Arctic Ocean. We resolve this contradiction by complementing SST data based on planktic foraminiferal abundances with surface salinity changes using hydrogen isotopic compositions of alkenones in a core from the central Nordic Seas. The data indicate the prevalence of a relatively cold, low‐salinity, surface water layer in the Nordic Seas during most of MIS 11. In spite of the low‐density surface layer, which was kept buoyant by continuous melting of surrounding glaciers, warmer Atlantic water was still propagating northward at the subsurface thus maintaining meridional overturning circulation. This study can help to better constrain the impact of continuous melting of Greenland and Arctic ice on high‐latitude ocean circulation and climate. Temperatures and salinities have been reconstructed in the Nordic Seas for Marine Isotope Stage 11A cold, low‐salinity, buoyant surface water layer persisted in the Nordic Seas during this periodThe buoyant surface water layer was formed due prolonged melting of glaciers

Newly discovered non-isoprenoid dialkyl diglycerol tetraethers containing 13,16-di- or 5,13,16-trimethyloctacosanyl moieties have been identified in peats and coastal marine and lake sediments by HPLC–MS and high-field NMR spectroscopy.

Two sediment cores from the western Arabian Sea, NIOP905 and 74KL, were analyzed to determine sea surface temperature (SST) variations over the last 23 kyr. Two organic molecular SST proxies were used, the well‐established U37K′based on long‐chain unsaturated ketones synthesized by haptophyte algae and the newly proposed TEX86derived from the membrane lipids of Crenarchaeota. Comparison of NIOP905 and 74KL core top data with present‐day SST (0–10 m) values indicates that both proxies yield temperatures similar to local annual mean SSTs. However, TEX86and U37K′SST down‐core records derived from the same cores differ in magnitude and phasing. The alkenone SST record of NIOP905 shows small changes in SST (∼0.5°C) over the last 23 kyr, while that of core 74KL shows a ∼2°C increase from the Last Glacial Maximum (LGM) (23–19 calendar (cal) kyr B.P.) through the Holocene (the last 11.5 cal kyr B.P.) synchronous with changes in the Northern Hemisphere. In contrast, the TEX86records of both cores show a large increase in SST from 22°–23°C in the LGM to 28°–30°C during Termination I (19–11.5 cal kyr B.P.), decreasing to present‐day annual means of ∼26°C. A cold phase between 14.5 and 12 cal kyr B.P. that may correspond to the Antarctic cold reversal is also observed. This implies a Southern Hemisphere control on tropical SST reconstructed by the TEX86, possibly related to SW monsoon. Our results suggest that the application of both TEX86and U37K′give different but complementary information on SST developments in past marine environments.

The stable carbon isotopic compositions of the inorganic carbon source, bulk cell material, and isoprenoid lipids of the hyperthermophilic crenarchaeon Metallosphaera sedula, which uses a 3-hydroxypropionate-like pathway for autotrophic carbon fixation, have been measured. Bulk cell material was approximately 3‰ enriched in 13C relative to the dissolved inorganic carbon, and 2‰ depleted in 13C relative to isoprenoid membrane lipids. The isotope data suggested that M. sedula uses mainly bicarbonate rather than CO2 as inorganic carbon source, which is in accordance with a 3-hydroxypropionate-like carbon fixation pathway. To the best of our knowledge this is the first report of 13C fractionation effects of such a hyperthermophilic crenarchaeon.

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A suite of six sterols, lanosterol, lanost-8(9)-en-3β-ol, 4,4-dimethylcholesta-8(14),24-dien-3β-ol, 4,4-dimethylcholest-8(14)-en-3β-ol, 4-methylcholesta-8(14),24-dien-3β-ol and 4-methylcholest-8(14)-en-3β-ol, were identified in the psychrophilic methanotrophic bacterium, Methylosphaera hansonii. Their presence suggests that the capacity for sterol biosynthesis in methanotrophic bacteria is limited to the family Methylococcaceae but which have widely different optimal growth temperatures.