HR: 1340h
AN: PP23B-1418    [Abstracts]
TI: Organic Carbon Accumulation in the Late Quaternary Santa Barbara Basin: A Comparison of Deep and Shallow Sites
AU: * Zeleski, C M
EM: czeleski@saddleback.edu
AF: Saddleback Community College, 28000 Marguerite Parkway, Mission Viejo, CA 92692 United States
AU: Behl, R J
EM: behl@csulb.edu
AF: California State University, Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840 United States
AB: Two giant piston cores obtained during the IMAGES MONA Cruise (2002) from central/deep (569 m) and marginal/shallow (481 m) sites in Santa Barbara Basin, CA, present a special opportunity for testing the relative importance of different environmental criteria for the preservation of organic carbon. The cores were deposited within and above the low-oxygen upper intermediate water mass, recording more consistently dysoxic (deep core) and consistently oxygenated (shallow core) settings. Samples were analyzed at 20 cm spacing ($\sim$140 yr) for total organic carbon (TOC), carbonate (CaCO3), C/N ratios, grain size and the mass accumulation rates of TOC and CaCO3 (MARTOC and MARCaCO3) from late Marine Isotope Stage 3 through the Holocene. As indicated by C/N ratios, the organic matter in both cores is a mixture of marine and terrigenous sources. Both TOC profiles display asymptotic curves that decrease with depth with little variation lower in the core in spite of significant changes in climate, bioturbation/lamination, and benthic foraminiferal populations. This confirms that anoxia, as indicated by sedimentary fabric and benthic populations, is not a prerequisite for enhanced organic matter preservation. MD2504, in the shallower slope setting, has sediments that are primarily coarser and organic components that are more marine in composition (including shell fragments). MD2503, the deep basinal core, primarily has very fine-grained sediments originating with a more terrigenous signature, suggesting more efficient routing of Santa Clara River-derived materials to the basin center than to the more proximal slope setting. The best correlations (covariation) in MD2503 are positive (TOC vs. C/N ratios and MARTOC vs. C/N ratios) during cold, oxygenated intervals of the Last Glacial Maximum, and Younger Dryas implying that for these climatic intervals, TOC correlates with the proportion of organic matter coming from terrigenous sources. During the Preboreal and Holocene in MD2504, times of warmth and higher sea level, the TOC increased when low C/N ratios indicate more marine-sourced organic matter. Peaks in percent silt during the Heinrich 1 event, the Younger Dryas and Preboreal intervals are possibly related to changes in precipitation or in distribution of river sediments associated with sea-level fluctuation.
DE: 4806 Carbon cycling
DE: 4863 Sedimentation
DE: 4243 Marginal and semienclosed seas
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting