This research is focused on determining the phosphate sources, reactions and time-scales involved in the precipita- tion and aging of authigenic phosphate in sediments of Santa Barbara Basin, California. Preliminary data from the basin indicate that authigenic phosphate is precipitating from pore waters within the upper 25 cm of the sediment column. These data also suggest that high concentrations of dissolved phosphate in the uppermost centimeter are coupled to a mat of filamentous sulfur-oxidizing bacteria, Beggiatoa spp., which blankets the sediment-water interface. The field portion of the program will include 1) seasonal collections of the mat and underlying sediments for fine-scale biomass, pore water and solid phase sampling, and 2) in situ measurements of millimeter -scale gradients of pore water oxygen and pH. In the labora- tory, investigations will be conducted of the petrology, mineralogy, chemistry, and isotopic compositions of individual sediments lamina and separated phosphatic phases. These latter efforts should provide definitive data for evaluating the nature, stability, and accumulation rates of phases precursory to carbonate fluorapatite. The contribution of Beggiatoa biomass to the total diagenetic phosphate flux, as well as the influence of the chemical microenvironment of the mat on other mechanisms of phosphate regeneration, such as iron-oxyhydroxide shuttling, will also be determined. Overall, the results will contribute to our understanding of the primary processes that remove phosphorus from the ocean to the global sedimentary reservoir.
