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Productivity influences on oxygenation of the Santa Barbara Basin, California, during the late Quaternary Ivanochko, Tara S.

Abstract

Short-term fluctuations in the bottom water oxygen content of Santa Barbara Basin have been previously recognized from variations in a sedimentary bioturbation index (Behl and Kennett, 1996). A correlation between such anoxic events in the basin and Dansgaard-Oeschger interstadials, as measured from δ180ice in Greenland ice cores, was then used by the same authors to relate variations in bottom water oxygenation to high-frequency changes in the ventilation of the Santa Barbara Basin, driven by pan-hemispheric changes in climate transmitted through the atmosphere. An additional control on the oxygen content at depth is the local settling flux of metabolizable organic matter. Trace metal measurements from closely-spaced sediment samples are used here to distinguish oxygen depletion resulting from local increases in export production from oxygen depletion introduced by the importation of O2-poor water. Molybdenum, Re, U, Cd, and Ag and interelement ratios are used in conjunction with organic carbon concentrations, opal fluxes, and δ15N measurements to deduce into past redox conditions of the basin, variations in the depth of the redox boundary and the flux of organic material to the basin floor. Comparisons between ODP Holes 893A (Santa Barbara Basin), 1019 and 1017 (both California margin) allows one to distinguish of regional signals dominated by ventilation changes from local signals dominated by vertical organic flux. During the Holocene, variations in productivity appear indeed to have impacted the oxygen content of the Santa Barbara Basin bottom waters. However, anoxic events concurrent with the Bolling-Allerod and during the last glacial interval are regional events associated with intermediate water mass characteristics.

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