HR: 08:15h
AN: PP51G-02 INVITED     [Abstracts]
TI: Diagenetic Controls on the Age Distribution of Marine Sedimentary Components
AU: * Eglinton, T I
EM: teglinton@whoi.edu
AF: Woods Hole Oceanographic Inst., Marine Chemistry and Geochemistry Dept. Fye Laboratory, MS#4, Woods Hole, MA 02543 United States
AU: Mollenhauer, G
EM: gmollenhauer@whoi.edu
AF: Woods Hole Oceanographic Inst., Marine Chemistry and Geochemistry Dept. Fye Laboratory, MS#4, Woods Hole, MA 02543 United States
AU: Ohkouchi, N
EM: nohkouchi@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution (IFREE), 2-15 Natsushima-cho, Yokosuka, 237-0061 Japan
AU: Hayes, J M
EM: jhayes@whoi.edu
AF: Woods Hole Oceanographic Inst., Geology & Geophysics Dept. McLean Laboratory, MS#8, Woods Hole, MA 02543 United States
AU: Montlucon, D
EM: dmontlucon@whoi.edu
AF: Woods Hole Oceanographic Inst., Marine Chemistry and Geochemistry Dept. Fye Laboratory, MS#4, Woods Hole, MA 02543 United States
AB: Molecular-level radiocarbon studies of source-specific biomarkers have revealed that different components isolated from marine surface sediments can exhibit a wide spectrum of apparent ages. Biogenic materials (e.g., phytoplankton detritus) raining down from the overlying surface ocean deliver modern sources of carbon to the sea floor. "Old" organic carbon (OC) can reflect terrigenous inputs, such as kerogen from sedimentary rock weathering or products of terrestrial photosynthesis stored in intermediate reservoirs (e.g., soils) on the continents. The presence of "pre-aged" marine OC in surface sediments indicates the occurrence of advective processes that result in redistribution of organic matter associated with low-density aggregates or fine-grained particles. These latter inputs contribute to the typically greater radiocarbon age of bulk OC relative to that of co-deposited planktonic foraminifera in surficial sediments. Once deposited, further changes in age distribution may occur by virtue of the differing reactivities and modes of delivery of organic matter inputs. In particular, recently produced biogenic materials may be preferentially degraded relative to allochthonous terrigenous and marine organic components as a result of the intrinsic chemical stability of the latter or their physical association with mineral matrices. Diagenetic changes in the proportions of these different inputs shape the sedimentary record and influence interpretation of corresponding proxies. Moreover, climate-driven changes in depositional conditions under which sedimentary components are buried likely modulate their degree of preservation. In order to investigate the influence of diagenetic processes on molecular and microfossil records, we have examined radiocarbon age relationships between different components (algal and terrestrial biomarkers, bulk OC, planktonic foraminifera) of surficial sediments recovered from a range of depositional regimes. We compare age distributions in surface sediments from settings that receive similar inputs but differ in bottom oxygen content, as well as between core samples taken within and below the sediment mixed layer. We discuss the importance of pre- and post-depositional processes on the formation of the sedimentary biomarker record and their implications for interpretation of molecular and microfossil proxies.
DE: 4806 Carbon cycling
DE: 4267 Paleoceanography
DE: 3022 Marine sediments--processes and transport
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting