EVOLUTIONARY CHANGES OVER THE LAST 1000 YEARS OF REDUCED SULFUR PHASES AND ORGANIC-CARBON IN VARVED SEDIMENTS OF THE SANTA-BARBARA BASIN, CALIFORNIA

Sediments from the Santa Barbara Basin (SBB) of the last 1000 years were analyzed for elemental sulfur (S(e)), mineral sulfide sulfur (S(m)), lipid-based organically bound sulfur (S(x)), residual organically bound sulfur (S(o)), total organic carbon (TOC), and total nitrogen (TN). The approximate annual resolution of the time-series data permitted us to evaluate the influence of oceanic variables on the benthic environment and the accumulating varved sediment in the SBB. A bacterial mat community at or near the sediment surface is influencing sediment porosity and the production and distribution of S(e). Early diagenesis dampens the amplitude of environmental signals in the geochemical time series. The concentrations of S(m) and S(o) increase with burial depth, at the expense of decreasing concentrations of S(x) and S(e). At depths greater than 5.5 cm, corresponding to an age of 7 years, S(m) becomes the largest pool of reduced sulfur. It requires approximately 500 years of primarily bacterially mediated diagenesis, equivalent to a burial depth of approximately 1.4 m, for SBB sediments to gradually approach and finally enter the region assumed to represent typical ''normal'' marine sediments on a plot of weight percent TOC vs. S(m).