HIGH-RESOLUTION SEDIMENTARY RECORDS OF PRIMARY PRODUCTIVITY AND ORGANIC MATTER ACCUMULATION IN THE SANTA BARBARA BASIN, CALIFORNIA, COMPARED TO NORTHEAST PACIFIC METEOROLOGICAL DATA FOR THE 20TH CENTURY

Marine primary productivity and organic matter accumulation were investigated using sediments from the Santa Barbara Basin (SBB) in the northeastern Pacific Ocean. A 53-cm core was collected from the center of the laminated sediment zone at 590 m water depth in SBB. The core was sectioned at 1-cm intervals, giving a calendar age range of ~1860-2000 after common era (ACE) and sample resolution of approximately two years. Several sedimentary tracers of export production (organic carbon, calcium carbonate, biogenic silica, excess barium and excess uranium) and nutrient burial (organic and reactive phosphorus) were measured. These geochemical data were compared to meteorological data (Pacific Decadal Oscillation [PDO] and upwelling indices, Sea Surface Temperatures) available for the 20th century.

Primary productivity (as reflected by the sedimentary proxies) decreased throughout the study interval toward the present, consistent with hypothesized ‘spin-down' of the California Current System. Two transitions occur in the productivity records, both coincident with climatic shifts to a warm PDO regime. Productivity decreased after ~1970, consistent with expectation for the California Current after the most recent switch to warm PDO regime, and consistent with the hypothesis that decreased organic carbon rain may be responsible for a return to bioturbated sediments at the edges of the southern California borderland basins. Thus, although the magnitude of production did not change dramatically during the study interval, primary productivity does appear to have responded to interdecadal scale changes in the mean state of climate at this northeastern Pacific site. However, climatic fluctuations alone do not entirely explain variability in the proxy records. Hence it is possible that, in addition to productivity changes and subsequent redox changes, other processes (e.g., sediment delay and redistribution on shelves and/or tidal forcing) also contribute to driving accumulation of the proxies.