A76 Goldschmidt Conference Abstracts 2005 in the Environment

How widespread are Archaeal lipids Metabolic capabilities of prokaryotes in sedimentary systems? in the deep ocean 1 2 1 1 1 2 R.D. PANCOST , S. SCHOUTEN , J. COLEMAN , R.L. HANSMAN , L.I. ALUWIHARE , A. PEARSON , 1 1 1 2 3 C.S.BOOT , S.P.KELLY , AND B.E.VAN DONGEN S.R. SHAH , AND A.E. INGALLS 1Organic Geochemistry Unit, Bristol Biogeochemistry 1Geosciences Research Division, Scripps Institution of Research Center, School of Chemistry, University of Oceanography, 9500 Gilman Drive, La Jolla, CA Bristol, Cantocks Close, Bristol BS8 1RJ, UK ([email protected], [email protected]) (R.D.Pancost@ Bristol.ac.uk) 2Department of Earth and Planetary Sciences, Harvard 2Department of Marine Biogeochemistry and Toxicology, The University, College Avenue, Cambridge, MA Royal Netherlands Institute of Sea Research (NIOZ), The ([email protected], [email protected]) Netherlands. ([email protected]) 3School of Oceanography, University of Washington, Box 355351, Seattle, WA ([email protected]) Over the past fifteen years, new analytical developments in microbiological approaches have led to the identification of Rapid advances in molecular biological techniques have Archaea in almost all environments. However, comparable enabled a more detailed study of and evidence for archaeal ubiquity from lipid biomarkers, such as microbial communities in their environment. However, the dialkyl diethers (DGDs) and glycerol dialkyl glycerol microbial ecology of newly discovered phylogenetic groups tetraethers (GDGTs), has been less consistent. In part, this and their roles in various biogeochemical cycles remain reflects the quantitative nature of biomarker approaches, such elusive. Here we employ the geochemical tracer radiocarbon that they are typically found where Archaea comprise a (14C) to assess the sources of carbon that fuel prokaryotic significant portion of the biomass (e.g. sediments associated production in the mesopelagic ocean. The radiocarbon ages of with or anaerobic methanotrophy (AOM); carbon pools (DIC, total DOC, and POC/new DOC) in the extreme environments; pelagic sediments). However, lack of sub-surface ocean are distinct, which makes 14C an ideal tracer attention and difficulty in analysis has also contributed to the for investingating carbon flow into the dark ocean’s biosphere. relative lack of archaeal lipid reports. Here, we survey a range Radiocarbon dates of nucleic acids extracted from of terrestrial and marine sediments and show that both DGDs microorganisms living at various depths in the Subtropical and GDGTs are highly widespread. North Pacific Ocean demonstrate that the fraction of 14C- In sites where Archaea are important mediators of depleted (old) intracellular carbon increases as the supply of biogeochemical processes, archaeal lipids can be the most fresh organic carbon diminishes. Based on isotopic signatures abundant compounds in total lipid extracts. These include of these nucleic acids and available carbon pools at each cold seeps, characterised by AOM, and extreme geothermal depth, we estimate the age of the substrate(s) fueling systems. However, we also observe archaeal lipids, albeit at prokaryotic production in both surface and mesopelagic concentrations several orders of magnitude lower than waters. Using molecular biological and lipid biomarker observed at seeps, in marine sediments characterised by analyses we further estimate the depth-dependent contribution diffusive methane flux and very low AOM rates. We also of Group I Archaea to the total prokaryotic community in our observe DGDs (archaeol and sometimes hydroxy- archaeol) samples and the ∆14C signature of carbon fueling archaeal and GDGTs at all methanogenic settings examined, including production. This is the first in-situ investigation of the carbon those where rates are very low. This suggests that such metabolism of microorganisms inhabiting the sub-surface biomarkers should be common in the sedimentary record, ocean and it provides direct evidence for the uptake of old being found where sulfate is depleted and organic matter carbon by prokaryotes in the deep ocean. oxidation proceeds via methanogenesis. Indeed, we have found archaeol in Pleistocene Amazon Fan and Benguela Upwelling Region sediments, Holocene estuarine sediments, and Cenozoic coastal margin sediments (Tanzania). Thus, archaeal lipids are widespread and can be an important component of biomarker-based evaluation of ancient depositional environments.