HR: 1340h
AN: PP23B-1412    [Abstracts]
TI: Holocene Sedimentation In The Southern Gulf Of California And Its Climatic Implications
AU: * Gonzalez-Yajimovich, O
EM: yajimo@usc.edu
AF: University of Southern California Earth Sciences, 3651 Trousdale Ave., Los Angeles, CA 90089 United States
AU: Douglas, R G
EM: rdouglas@usc.edu
AF: University of Southern California Earth Sciences, 3651 Trousdale Ave., Los Angeles, CA 90089 United States
AU: Gorsline, D S
EM: gorsline@usc.edu
AF: University of Southern California Earth Sciences, 3651 Trousdale Ave., Los Angeles, CA 90089 United States
AB: Alfonso Basin on the western side of the Gulf of California and Pescadero Basin on the center slope of the east side of the gulf are margin basins which have sills or shoreward slopes in the Oxygen Minimum Zone and preserve primary varves whose physical and associated geochemical characteristics yield information on Holocene climate and oceanographic changes in the gulf. Primary productivity and sedimentation in the gulf are related to the dominant wind fields and the sediment record can be considered as an imperfect proxy of climate. Here we examine the sediment components in multicores, box and gravity cores recovered during cruises from 1994 to 2001 and show that the sediments provide an important history of the changing environment. Laminated, hemipelagic mud, accumulating at rates of 25-50 cm/kyr, were sampled at 1 cm intervals to produce a high resolution record of organic carbon, calcium carbonate (foraminifera and coccoliths), opal silica (diatoms, radiolaria) and terrigenous content, that was examined for variations in accumulation and preservation. Alfonso Basin sediments are organic carbon-rich (5-7%) with varying amounts of calcium carbonate (1-25%) and little opal silica ($<$4%). Pescadero Basin sediments are also organic carbon-rich (2.5-4.3%) but contain less carbonate (0-6%) and more silica (8-21%). Changes on the sedimentation pattern for biogenic and terrigenous records occurred starting circa 7,200 YBP with major shifts occurring at 4200, 3000 and YBP typified by carbonate maxima. Smaller changes occurred at 1500, 950, and 400 YBP. Changes can be observed in both basins suggesting the events occurred across the whole southern gulf. The stepwise decrease in mass accumulation rates at 3000 and 1500 YBP indicate a shift of conditions that can be correlated to fall insolation records for the northern hemisphere, creating stronger NW winds and inhibiting the summer rains. Biogenic records (Opal and Carbonate) indicate a drop in productivity and terrigenous mud records suggest a shift from wetter to dryer conditions and perhaps from fluvial to eolic sedimentation. At 400 YBP a recovery is observed suggesting a return to wetter less windy conditions. These shifts also are reflected in sediment lamination. Three general periods are recognized; Early period (10,000-7,200 YBP) with high productivity and variability resulting from strong northwesterly winds and upwelling. Middle period (7,200-4,200 YBP) a stable period with steady decrease in productivity. And Late period (4,200 YBP to the present) with constant primary productivity suggested by opal fluxes, and with an increase in the carbonate-opal east-west asymmetry. Spectral analysis shows a 1-2 kyr climate rhythm in the Gulf and the data suggest that it is mediated by the migration of the Intertropical Convergence Zone (ITCZ) due to orbital precession. The records are marked by strong climate-ocean variability cycles with two modes: 210 years (throughout the record) and 800 years (after 3000 YBP) that appear related to latitudinal shifts of the ITCZ, produced by solar cycles.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting