Determining the influences of Late Quaternary ventilation and productivity variations on Santa Barbara Basin sedimentary oxygenation: a multi-proxy approach

A correlation between warm interstadials implied by δ 18O ice in the GISP (Greenland) ice core and anoxic events recorded by the sediments drilled at ODP Site 893 in Santa Barbara Basin (SBB), has been used previously to relate variations in bottom water oxygenation to high-frequency changes in the ventilation of the SBB (Nature, 379 (1996) 243). However, an additional control on the oxygen content at depth is the local settling flux of metabolizable organic matter. To assess the impact of oxygen consumption related to this source, Mo, Cd, Re and U concentration data are used here in conjunction with % C Org and δ 15N to deduce past redox conditions, variations in the sedimentary redox boundary depth and the impact of local organic flux on the oxygenation of SBB deep waters. Comparisons between ODP Sites 893, 1017 and 1019 allow the differentiation of regional signals, dominated by ventilation changes, from local signals, dominated by vertical organic flux. It is concluded that prior to the Holocene, local productivity changes in the Santa Barbara Basin are not solely the cause of sedimentary anoxia. Episodic injections of low oxygen intermediate water, identified on the regional scale, strongly influenced the oxygen content of the SBB during this time. However, over the last 10,000 years the influence of local productivity has increased and the regional similarity among the three sites is complicated by local signals.