HR: 1340h
AN: PP43B-1286    [Abstracts]
TI: Tracking Soil Organic Carbon Transport to Continental Margin Sediments Using Soil-Specific Hopanoid Biomarkers: a Case Study From the Congo Fan (ODP Site 1075)
AU: * Cooke, M P
EM: M.P.COOKE@NCL.AC.UK
AF: Newcastle University, School of Civil Engineering and Geosciences Drummond Building, Newcastle upon tyne, NE1 7RU, United Kingdom
AU: Talbot, H M
EM: H.M.Talbot@ncl.ac.uk
AF: Newcastle University, School of Civil Engineering and Geosciences Drummond Building, Newcastle upon tyne, NE1 7RU, United Kingdom
AU: Eniola, O
EM: Olubunmi.Eniola@ncl.ac.uk
AF: Newcastle University, School of Civil Engineering and Geosciences Drummond Building, Newcastle upon tyne, NE1 7RU, United Kingdom
AU: Zabel, M
EM: mzabel@uni-bremen.de
AF: Newcastle University, School of Civil Engineering and Geosciences Drummond Building, Newcastle upon tyne, NE1 7RU, United Kingdom
AU: Zabel, M
EM: mzabel@uni-bremen.de
AF: University of Bremen, Geochemistry and Hydrogeology Klagenfurter Strasse, Bremen, 28359, Germany
AU: Wagner, T
EM: thomas.wagner@ncl.ac.uk
AF: Newcastle University, School of Civil Engineering and Geosciences Drummond Building, Newcastle upon tyne, NE1 7RU, United Kingdom
AB: The transport and subsequent deposition of terrestrially derived organic matter into the ocean is an important but poorly constrained aspect of the modern global carbon cycle. In regions associated with large river systems it is likely that the terrestrial input of organic carbon is much more complex than commonly considered and very difficult to trace based on established geochemical proxies. It is therefore important to develop proxies that target the movement and fate of this terrestrial organic material. The identification of bacteriohopanepolyol (BHP) biomarkers unique to soil derived organic carbon (SOC) has enabled the transport of SOC into aquatic sediments to be traced. The extreme recalcitrance of BHPs enables these source specific compounds to be used on recent and ancient sediments to identify periods of high and low SOC input into sediments. BHPs are bacterial membrane compounds with a high degree of structural variability. They are analogous to steroids in eukaryotes and have been identified in over half of all bacteria studied for their presence. BHPs have a wide range of over 40 functional groups on the side chain, with up to 6 functional groups in each structure, and with methylation and unsaturation over 100 total structures have been identified1. During the BHP analysis of a wide range of soils from around the world we consistently measure high levels adenosylhopane, known to originate from purple non-sulphur, nitrogen fixing and ammonia oxidising bacteria and 2-methyl adenosyl hopane (m/z 802)2, from nitrogen fixing bacteria. Only 3 lacustrine sediments with large SOC supply from their catchments areas have been found to contain these markers in a survey of over 40 different non-marine settings. Recent studies on Late Quaternary sediments from the Congo deep sea fan (OPD site 1075, approximately 2 km water depth) provide a strong case to expect markers for SOC3. An initial analysis of the core samples confirms the presence of soil specific BHP markers in each sample analyzed down to 89 m depth in addition to the presence of common sediment associated BHPs. Concentrations of soil markers are high in the upper sediment section down to about 49 m supporting the case for these molecular markers as novel proxies for SOC supply and burial. Distinct peaks of adenosyl and 2 methyl adenosyl hopane at about 200, 300 and 550 kyrs tentatively imply that the rate of terrestrial organic matter discharge from tropical Africa significantly increased at these times, possibly associated with periods of reduced soil stability in the Congo catchment. Analysis of the surface sediments from 4 other cores in close proximity to ODP site 1075 clearly shows that the percentage contribution of soil marker BHPs decreases with increasing distance from the river mouth, indicating that the river is the source of these BHPs. References 1. Rohmer, M. 1993. Pure and Applied Chemistry 65, 1293-1298. 2. Talbot, H.M., Rohmer, M., Farrimond, P., 2007. Rapid Communications in Mass Spectrometry (In press). 3. Holtvoeth, J., Wagner, T., Kolonic, S., 2005. Geochimica et Cosmochimica Acta, 69, 2031-2041.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0424 Biosignatures and proxies
DE: 0428 Carbon cycling (4806)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting