BIOGENIC SEDIMENTATION BENEATH THE CALIFORNIA CURRENT SYSTEM FOR THE PAST 30 KYR AND ITS PALEOCEANOGRAPHIC SIGNIFICANCE

A north-south transect of 17 cores was constructed along the eastern b oundary of the California Current system from 33 degrees to 42 degrees N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, C-org, and b iogenic opal were assembled at 500 to 1000 years/sample to provide rel atively high resolution. Time-space maps reveal a complex pattern of c hanges that do not follow a simple glacial-interglacial two-mode model . Biogenic sedimentation shows responses that are sometimes time-trans gressive and sometimes coeval, and most of the responses show more con sistency within a limited geographic area than any temporal consistenc y. Reconstructed conditions during late oxygen isotope stage 3 were mo re like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased du ring the last glacial interval in the central California region, and t he waters of the southern California margin had relatively low product ivity. Productivity on the southern Oregon margin was relatively low a t the beginning of the last glacial interval, but by about 20 ka, prod uctivity in this area significantly increased. This change suggests th at the center of the divergence of the West Wind Drift shifted south a t this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increase d upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (<300 years) decr ease in CaCO3, C-org, and biogenic opal occurred at 13 ka. The changes suggest a major reorientation of the atmospheric circulation in the N orth Pacific and western North America and the establishment of a stro ng seasonality in the central California region. A carbonate preservat ion event occurred at 10 ka that appears to reflect the uptake of CO;! by the terrestrial biosphere as the northern latitudes were reforeste d following retreat of the glaciers. The Holocene has been a period of relatively high productivity in the southern California margin, relat ively strong coastal upwelling along the central California margin, re latively weak upwelling along the northern California margin, and the northward migration of the divergence zone of die West Wind Drift.