DECADAL-SCALE CLIMATE VARIABILITY IN THE NORTHEAST PACIFIC OXYGEN MINIMUM ZONE: EVIDENCE FROM CARBONATE AND ORGANIC CARBON RECORDS

Sediment cores collected within the Oxygen Minimum Zone (O2 <5 µm/kg; 400-1300 m depth) from off the coast of Baja California at 25°N during a 1999 R/V Melville cruise present the most southerly evidence of decadal-scale climate instability yet observed on the open Northeast Pacific margin. The development of high resolution proxies through statistical analysis of extensive Diffuse Spectral Reflectance (DSR) data sets provides the framework for gauging rapid shifts in carbonate and organic carbon within the spatial/temporal bounds of the Oxygen Minimum Zone from the last deglaciation to the Holocene (15 to 0 Ka). These shifts are potentially controlled by changes in local primary production or sub-surface water mass ventilation, however the relative importance of each process over this time scale is not well understood. This study focuses on five 10 to 14m piston cores collected within the Soledad Basin, desirable for its high sedimentation rates (100-120cm/kyr) and its 200m sill depth. We maintain the hypothesis that variations in carbonate and organic carbon seen through the Diffuse Spectral Reflectance (DSR) will preferentially show the effects of local production on the spatial/temporal extent of the Oxygen Minimum Zone due to the restrictions imposed on the basin by its shallow sill depth. This record will be compared with sites along the open margin to further characterize the contributions of primary production and water mass ventilation to the intensity of the Oxygen Minimum Zone. Carbonate and organic carbon shifts within the Soledad record also contain a periodicity within the time scale bounds of the present day Pacific Decadal Oscillation (20-50 year quasi-cyclicity); suggesting a connection between the two processes. The record has also shown a strong positive correlation to the dO18 variations within the GISP2 ice core record of Grootes and Stuvier (1997) through which we hope to further elucidate rapid climate teleconnections between high and low latitude climate instability during the past 15 Ka.