HR: 1340h
AN: PP43B-1252    [Abstracts]
TI: D/H Ratios of Terrestrial Lipids from Santa Barbara Basin: A Preliminary Assessment of Paleoclimatic Relevance
AU: Sessions, A L
EM: als@gps.caltech.edu
AF: Division of Geological & Planetary Sciences, California Institute of Technology, MC100-23, Pasadena, CA 91125, United States
AU: * Li, C
EM: chaoli@ucr.edu
AF: Division of Geological & Planetary Sciences, California Institute of Technology, MC100-23, Pasadena, CA 91125, United States
AU: Valentine, D L
EM: valentine@geol.ucsb.edu
AF: Department of Geological Sciences, University of California, Santa Barbara, Webb Hall, Bldg 526, Santa Barbara, CA 93106, United States
AU: Thiagarajan, N
EM: nivedita@caltech.edu
AF: Division of Geological & Planetary Sciences, California Institute of Technology, MC100-23, Pasadena, CA 91125, United States
AB: Hydrogen isotope (D/H) ratios in sedimentary lipids are increasingly used as a proxy for terrestrial paleoclimate. In arid regions such as southern California, one of the principle problems is finding long-lived lakes to provide the necessary sedimentary archive for this proxy. As a potential alternative, here we explore the D/H record of terrestrial lipids preserved in a marginal marine suboxic basin, Santa Barbara Basin (SBB). Rapid sedimentation, long continuous records, significant terrestrial inputs, and excellent organic preservation all make this site attractive from a geological perspective. But does it record terrestrial climate? To test this, we conducted a survey of lipid D/H ratios in a sediment core collected at the depocenter of SBB, extending back 1200 years before present. Long-chain fatty acids, derived from terrestrial leaf waxes, exhibit virtually no downcore variation in D/H and are uncorrelated with the record of winter Palmer Drought Severity Index (PDSI) in southern California, a proxy for regional precipitation. Long-chain n-alkanes, also derived from leaf waxes, show considerable downcore variability in D/H but are also uncorrelated with PDSI. We believe the temporal variability for n-alkanes may be caused in part by addition of D-enriched fossil hydrocarbons due to increased erosion during wet periods. Regardless, none of these leafwax compounds are a robust paleoclimate proxy in SBB at < 1000-year timescales. In contrast, D/H ratios of n-C22:0 and n-C24:0 fatty acids, commonly attributed to terrestrial aquatic sources, are well correlated with PDSI over this time interval and could serve as a viable paleoclimate proxy. We tentatively attribute the discrepancy between leaf-wax and aquatic biomarkers to a much longer soil residence time for leaf-wax compounds in the watershed, which effectively masks changes over centennial timescales.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 4914 Continental climate records
DE: 4994 Instruments and techniques
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting