Description: The newly introduced temperature proxy, the tetraether index of archaeal lipids with 86 carbon atoms (TEX86), is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether (GDGT) lipids of marine Crenarchaeota. The composition of sedimentary GDGTs used for TEX86 paleothermometry is thought to reflect sea surface temperature (SST). However, marine Crenarchaeota occur ubiquitously in the world oceans over the entire depth range and not just in surface waters. We analyzed the GDGT distribution in settling particulate organic matter collected in sediment traps from the northeastern Pacific Ocean and the Arabian Sea to investigate the seasonal and spatial distribution of the fluxes of crenarchaeotal GDGTs and the origin of the TEX86 signal transported to the sediment. In both settings the TEX86 measured at all trap deployment depths reflects SST. In the Arabian Sea, analysis of an annual time series showed that the SST estimate based on TEX86 in the shallowest trap at 500 m followed the in situ SST with a 1 to 3 week time delay, likely caused by the relatively low settling speed of sinking particles. This revealed that the GDGT signal that reaches deeper water is derived from the upper water column rather than in situ production of GDGTs. The GDGT temperature signal in deeper traps at 1500 m and 3000 m did not show a seasonal cyclicity observed in the 500 m trap but rather reflected the annual mean SST. This is probably due to a homogenization of the TEX86 SST signal carried by particles as they ultimately reach the interior of the ocean. Our data confirm the use of TEX86 as a temperature proxy of surface ocean waters.

Description: Anaerobic oxidation of ammonium (anammox) is an important process in the marine nitrogen cycle. It has been estimated to contribute up to 50% of nitrogen loss from the ocean, and is especially prevalent within oxygen minimum zones (OMZs). Here we studied the presence and distribution of anammox in the extended OMZ of the Eastern Tropical North Pacific (ETNP) using ladderane fatty acids, specific biomarkers for anammox bacteria. The validity of ladderane fatty acids as proxies for anammox bacteria was demonstrated by their excellent correspondence with anammox 16S rRNA functional gene abundances and their expression and intact polar ladderane lipid concentrations in suspended particulate matter (SPM) from the Arabian Sea. In the ETNP, SPM was collected from various water depths at four stations along a northwest to southeast cruise transect and ladderane fatty acids were analyzed at each station. In all SPM samples where ladderane lipids were detected, C18 ladderane fatty acids were on average 5 fold more abundant than C20 ladderane fatty acids. Maximum concentrations in ladderane fatty acids (1.1 - 2.3 ng/l) were recorded at 400-600 m water depth, often corresponding to the depth of the secondary nitrite maximum. In one of the four stations, a second maximum in the ladderane fatty acid concentration was noted at a shallower depth (i.e. at 85 m), coinciding with higher nitrite concentrations at this water depth. The availability of nitrite probably limits anammox activity in the ETNP. Anammox lipids were abundant within the OMZ at all stations and concentrations were comparable to those in other OMZs, suggesting that anammox may be responsible for a significant loss of nitrogen in the OMZ of the ETNP.

Description: In this study we have analyzed sediment trap time series from five tropical sites to assess seasonal variations in concentrations and fluxes of long-chain diols (LCDs) and associated proxies with emphasis on the Long chain Diol Index (LDI). For the tropical Atlantic, we observe that generally less than 2 % of LCDs settling from the water column are preserved in the sediment. The Atlantic and Mozambique Channel traps reveal minimal seasonal variations in the LDI, similar to the TEX86 and UK'37. However, annual mean LDI-derived temperatures are in good agreement with the annual mean satellite-derived sea surface temperatures (SSTs). In the Cariaco Basin the LDI shows larger seasonal variation, as do the TEX86 and UK'37. Here, the LDI underestimates SST during the warmest months, which is likely due to summer stratification and the habitat depth of the diol producers deepening to around 20 to 30 m. Surface sediment LDI temperatures in the Atlantic and Mozambique Channel compare well with the average LDI-derived temperatures from the overlying sediment traps, as well as with decadal annual mean SST. Lastly, we observed large seasonal variations in the Diol Index, as indicator of upwelling conditions, at three sites, potentially linked to Guinea Dome upwelling (Eastern Atlantic), seasonal upwelling (Cariaco Basin) and seasonal upwelling and/or eddy migration (Mozambique Channel).

Description: Adenosyl-BHP abundances in Vancouver Island and Black Sea total suspended particulate matter and Cariaco sinking particulate organic matter samples were analyzed to study in situ production in oxygen minimum zones. Water column suspended particulate matter samples were obtained using McLane WTS-LV (standard configuration) in situ filtration systems from Vancouver Island fjords aboard R/V Barnes in 2007 and the Black Sea aboard R/V Knorr (cruise 172/8) in 2003. Sinking particulate organic matter was sampled in sediment traps as part of the CARIACO Ocean Time-Series Program in Cariaco Basin. Adenosyl-BHPs were analyzed in trap A (275 m water depth) and trap B (455 m water depth) for 14-day opening intervals from November 1999 through April 2000 and July 2002 through October 2002.

Description: A series of long-chain (C37, C38, C39), primarily di and tri-unsaturated methyl and ethyl ketones, first identified in sediments from Walvis Ridge off West Africa and from Black Sea (de Leeuw et al., 1979), has been found in marine sediments throughout the world (Brassell et al., 1986 doi:10.1038/320129a0). The marine coccolithophorid Emiliania huxleyi and members of the class Prymnesiophyceae are now the recognized sources of these compounds (Volkman et al., 1979; Marlowe, et al., 1984). Experiments with laboratory cultures of algae showed the degree of unsaturation in the ketone seris biosynthesized depends on growth temperature (Brassell et al., 1986; Marlowe, 1984), a physiological respons observed for classical membrane lipids (vanDeenen et al., 1972). Brassell and co-workers (Brassell et al., 198; Brassell et al., 1986b) thus proposed that systematic fluctuations in the unsaturation of these alkenones noted down-core in sediments from the Kane Gap region of the north-east tropical Atlantic Ocean and correlated with glacial-interglacial cycles provide an organic geochemical measure of past sea-surface water temperatures. Using laboratory cultures of E. huxleyi, we have calibrated changes in the unsaturation pattern of the long-chain ketone series versus growth temperature. The calibration curve is linear and accurtely predicts unsuturation patterns observed in natural particulate materials collected from oceanic waters of known temperature. We present evidence supporting the proposed paleotemperature hypothesis (Brassell et al., 1986, Brassel et al., 1986b) and suggesting absolute 'sea-surface temperatures' for a given oceanic location can be estimated from an analysis of long-chain ketone compositions preserved in glacial and interglacial horizons of deep-sea sediment cores.