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[N.sub.2]-fixing cyanobacteria play an essential role in sustaining primary productivity in contemporary oceans and freshwater systems. However, the significance of [N.sub.2]-fixing cyanobacteria in past nitrogen cycling is difficult to establish as their preservation potential is relatively poor and specific biological markers are presently lacking. Heterocystous [N.sub.2]-fixing cyanobacteria synthesize unique long-chain glycolipids in the cell envelope covering the heterocyst cell to protect the oxygen-sensitive nitrogenase enzyme. We found that these heterocyst glycolipids are remarkably well preserved in (ancient) lacustrine and marine sediments, unambiguously indicating the (past) presence of [N.sub.2]-fixing heterocystous cyanobacteria. Analysis of Pleistocene sediments of the eastern Mediterranean Sea showed that heterocystous cyanobacteria, likely as epiphytes in symbiosis with planktonic diatoms, were particularly abundant during deposition of sapropels. Eocene Arctic Ocean sediments deposited at a time of large Azolla blooms contained glycolipids typical for heterocystous cyanobacteria presently living in symbiosis with the freshwater fern Azolla, indicating that this symbiosis already existed in that time. Our study thus suggests that heterocystous cyanobacteria played a major role in adding 'new' fixed nitrogen to surface waters in past stratified oceans. nitrogen fixation | intact polar lipids | cyanobacterial biomarkers | symbiosis | saproprel doi/ 10.1073/pnas.1007526107

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 anammox-specific 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.sup.-1] sediment, with the highest concentrations detected at the sites located on the shelf at shallower water depths between 300 and 500 m. In contrast, the [C.sub.20] [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 [C.sub.20] [3]-ladderane monoether-PC lipid increased downcore in sediments located at greater water depths, showing highest concentrations of 1.2 x [10.sup.8] copies [g.sup.-1] sediment and 30 pg [g.sup.-1] sediment, 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 TE[X.sub.86] is a recently proposed paleothermometer through which ancient seawater temperatures of up to 120 My ago can be reconstructed. It is based on the relative distribution of glycerol dibiphytanyl glycerol tetraethers as measured by high-performance liquid chromatography/atmospheric pressure chemical ionizationmass spectrometry (HPLC/APCI-MS). The aim of this study was to examine and improve several analytical aspects in the determination of this important proxy in environmental matrices. Comparison of TE[X.sub.86] analysis using single ion mode (SIM) and mass scanning (m/z 950 to 1450) detection, respectively, revealed that SIM is up to 2 orders of magnitude more sensitive and that the TE[X.sub.86] can be determined with a reproducibility of [+ or -] 0.004 or [+ or -] 0.3 [degrees]C using this method. Comparison of TE[X.sub.86] values obtained with two different HPLC/APCI-MS setups revealed no significant differences. In addition, analysis of TE[X.sub.86] of extracts obtained by Soxhlet, ultrasonic, and accelerated high-pressure extraction techniques also showed no significant differences between the methods. Our results suggest that TE[X.sub.86] analysis by HPLC/APCI-MS is robust and can be determined with analytical errors comparable to those of other temperature proxies.

The Cretaceous has long been recognized as a time when greenhouse conditions were fueled by elevated atmospheric C[O.sub.2] and accompanied by perturbations of the global carbon cycle described as oceanic anoxic events (OAEs). Yet, the magnitude and frequency of temperature change during this interval of warm and equable climate are poorly constrained. Here we present a high-resolution record of sea-surface temperatures (SSTs) reconstructed using the [TEX.sub.86] paleothermometer for a sequence of early Aptian organic-rich sediments deposited during the first Cretaceous OAE (OAE1a) at Shatsky Rise in the tropical Pacific. SSTs range from ~30 to ~36[degrees]C and include two prominent cooling episodes of ~4 [degrees]C. The cooler temperatures reflect significant temperature instability in the tropics likely triggered by changes in carbon cycling induced by enhanced burial of organic matter. SST instability recorded during the early Aptian in the Pacific is comparable to that reported for the late AIbian-early Cenomanian in the Atlantic, suggesting that such climate perturbations may have recurred during the Cretaceous with concomitant consequences for biota and the marine environment. Keywords: [TEX.sub.86] index, oceanic anoxic events, Cretaceous sediments, carbon isotopes.

Paleoclimate studies of continental environments have been hampered by the lack of an independent paleotemperature proxy. A novel sea-surface temperature proxy has been proposed for marine systems based on membrane lipids of marine crenarchaeota (the [TEX.sub.86]--tetraether index of tetraethers with 86 carbon atoms). Analysis of archaeal membrane lipids in core-top sediments from a diverse suite of lacustrine systems suggests the ubiquitous occurrence of low-temperature crenarchaeota in lake systems as well. Application of the [TEX.sub.86] proxy in these lacustrine systems indicates that it is valid in lake environments, and the calibration of TEXs6 in lacustrine systems is similar to that in the marine environment. This proxy will provide an independent continental paleotemperature tool that will allow paleoclimatologists to address fundamental questions about temperature variability in continental environments and its relationship to climate change. Keywords: paleothermometer, lacustrine sediments, climate change, continental climate, biomarkers.

The middle Cretaceous (125-88 Ma) greenhouse world was characterized by high atmospheric C[O.sub.2] levels, the general absence of polar ice caps, and much higher global temperatures than at present. Both [delta][sup.18]O-based and model-based temperature reconstructions indicate extremely high sea-surface temperatures (SSTs) at high latitudes. However, there are a number of uncertainties with SST reconstructions based on [delta][sup.18]O isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the [delta][sup.18]O value of Cretaceous seawater, the paleoecology of middle Cretaceous marine organisms and seawater pH. Here we applied a novel SST proxy (i.e., [TEX.sub.86] [tetraether index of 86 carbon atoms], based on the membrane lipids of marine crenarchaeota) derived from middle Cretaceous sedimentary rocks deposited at low latitudes. The [TEX.sub.86] proxy indicates that tropical SSTs in the proto--North Atlantic were at 32-36[degrees]C during the early Albian and late Cenomanian-early Turonian. This finding agrees with SST estimates based on [delta][sup.18]O paleothermometry of well-preserved foraminifera as well as global circulation model calculations. The TEX86 proxy indicates cooler SSTs (27-32[degrees]C) for the equatorial Pacific during the early Aptian, which is in agreement with SST estimates based on [delta][sup.18]O paleothermometry. Keywords: Cretaceous, sea-surface temperature, [TEX.sub.86], tropics.

Author(s): Jaap S. Sinninghe Damsté (corresponding author) [1]; Marc Strous [2]; W. Irene C. Rijpstra [1]; Ellen C. Hopmans [1]; Jan A. J. Geenevasen [3]; Adri C. T. van Duin [...]

Research has been conducted on the crenarchaeotes and glycerol dibiphytanyl tetraethers of hyperthermophilic archaea in water samples from the Arabian Sea. The results of the quantitative analysis of these bacteria are presented.

A study was conducted to determine the effect of temperature on the ladderane lipid composition and distribution in anammox enrichment cultures, marine particulate organic matter, and surface sediments. The obtained results could be applied to discriminate between the origins of ladderane lipids in marine sediments.

A study was conducted to analyze the lipid composition of the mesophilic crenarchaeote isolated from 'Candidatus Nitrosopumilus maritimus' and examine both the core glycerol dialkyl glycerol tetraethers (GDGT) lipid composition and the intact polar lipid composition. The results revealed that the GDGTs are composed of hexose, dihexose, and/or phosphohexose head groups.

The microbial mats and sediments from various hot springs in Yellowstone National Park were analyzed. Results concluded that the Glycerol dialkyl glycerol tetraethers (GDGTs) bacteria are developed from geothermally heated surrounding soils.

The anaerobic oxidation of methane in sediment layers extending up to 17 centimeter deep at hydrothermal vent site suggests the presence of archaea that carryout methane oxidation anaerobically, as revealed by the distribution and isotopic analyses of lipids from sediment cores. Data show that these organisms are active at temperatures greater than 30 C and contain tetraether lipids.

Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and branched glycerol dialkyl diethers are main membrane constituents of cultured hyperthermophilic archaea and eubacteria, respectively, and are found in environments with temperatures [is greater than] 60 [degrees] C. Recently, we developed a new technique for the analysis of intact core tetraether lipids in cell material and sediments. The application of this technique to recent sediments shows that known and newly identified isoprenoid and branched GDGTs are widespread in low-temperature environments ([is less than] 20 [degrees] C) and are structurally far more diverse than previously thought. Their distribution indicates the ubiquitous environmental presence of as yet uncultivated, nonthermophilic organisms that may have independently evolved from hyperthermophilic archaea and eubacteria. The structures of some of the new GDGTs point to the hybridization of both typical archaeal and eubacterial biosynthetic pathways in single organisms.