Centennial-Scale Late Quaternary Stratigraphies of Carbonate and Organic Carbon from Santa Barbara Basin, Hole 893A, and Their Paleoceanographic Significance

Abstract

Stratigraphies of carbonate (CaCO3) organic carbon (Cora), CaCO3 and C,,rg mass accumulation rates (MAR), and paleoproductivity were determined with a sampling interval of 100 to 150 yr/sample for Ocean Drilling Program (ODP) Hole 893A from Santa Barbara Basin. Variations in CaCO3 with time do not show the typical Pacific pattern (higher during glacial periods), nor any pattern that can be related to glacial-interglacial cycles. Variations in total Cori! with time show four peaks of high values that occurred during Oxygen-Isotope Stage (OIS) 5 and earliest OIS-3. There is a moderate correlation between CaCO, and Corg mass accumulation rates. The fluxes of total sediment, CaCO3, and Corg are all an order-of-magnitude higher than occurred on the adjacent open continental margin. Paleoproductivity values, a proxy derived from an empirical correlation with Corg MAR, approached 250 gC/m2 yr during OIS-5 and OIS-1, and were <200 gC/m2 yr during all other times. Surprisingly, only percentage Corg shows a response to global climatic forcing with a precessional periodicity of 23 k.y./cycle, but only during OIS-5. Basin isolation during periods of lowered sea levels appears to have regulated Corg and CaCO, deposition by a mechanism related to the advection of California Current and California Counter Current waters. Fluctuations in strength or dissolved-oxygen content of the basin's bottom water are documented in lamination cycles, but did not significantly affect the preservation of CaCO3 and Core.