HR: 15:10h
AN: PP53A-07    [Abstracts]
TI: Exploring the Source of Sedimentary Archaeal Lipids by Comparative Radiocarbon Analysis of Alkenones and GDGTs.
AU: * Shah, S R
EM: shah@fas.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02139, United States
AU: Pearson, A
EM: pearson@eps.harvard.edu
AF: Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02139, United States
AU: Mollenhauer, G
EM: gmollenhauer@uni-bremen.de
AF: Fachbereich Geowissenschaften, University of Bremen, Am Handelshafen 12, Bremenhaven, D-28359, Germany
AU: Eglinton, T I
EM: teglinton@whoi.edu
AF: Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, 384 Woods Hole Road, Mail Stop 4, Woods Hole, MA 02543, United States
AB: The utility of biomarker-based paleotemperature proxies depends critically on the assumption that the alkenones of haptophyte algae or glycerol dialkyl glycerol tetraethers (GDGTs) of marine archaea are exported to the sediment and that they are buried quickly. However, lessons from compound-specific radiocarbon analysis of sedimentary organic matter have shown that sediments contain a heterogeneous mixture of organic compounds with different radiocarbon ages. More recent work has shown that even individual-compound radiocarbon values can represent contributions from differently-aged sources. In the case of the alkenones extracted from Bermuda Rise sediment cores, radiocarbon ages are offset from foraminiferal ages by up to 7000 years (1). This discrepancy indicates that the total sedimentary alkenone pool has a significant contribution from a pre-aged source in addition to export of surface production. This source of aged alkenones is believed to be their transport in association with fine-grained sediments. Presumably it is enabled in part by the relatively high resistance of alkenones to biodegradation. GDGTs also are highly resistant to degradation and are further complicated by the fact that they may be produced throughout the water column, not just at the surface. In this study, we present measurements of archaeal GDGTs from Santa Monica Basin, an area of pronounced sediment redistribution and focusing, and Bermuda Rise, a location known to accumulate drifting sediment. We account for the expected reservoir effect associated with archaeal autotrophy and use a mass balance model to constrain the amount of sedimentary GDGTs that may come from exported surface production rather than deep water column production or sediment re-distribution. The results suggest that paleotemperature reconstructions based on GDGTs and alkenones are affected similarly by sediment transport and that site selection is critical for accurate paleotemperature reconstructions. Reference: (1) Ohkouchi N, Eglinton TI, Keigwin LD, Hayes JM (2002) Science 298:1224-1227.
DE: 0424 Biosignatures and proxies
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting