PHORBIN STERYL ESTERS IN BLACK-SEA SEDIMENT TRAPS AND SEDIMENTS - A PRELIMINARY EVALUATION OF THEIR PALEOOCEANOGRAPHIC POTENTIAL

The distributions of pyropheophorbide-a steryl esters in one-year depl oyments of sediment traps at two locations in the Black Sea are descri bed. In nearly all our trap samples, phorbin steryl esters (PSEs) cont ribute a significant portion of the total phorbin flux. The relative a bundances of sterols esterified to pyropheophorbide-a varied throughou t the year, and we suggest these changes result from the observed seas onal variation of phytoplankton species in the overlying water column. The distribution of free sterols in a one-year composite sediment tra p sample closely approximates the distribution of sterols derived from the hydrolysis of sedimentary PSEs collected at an adjacent site. Fro m these results, we suggest that the distribution of sedimentary PSE s terols provides a record of sterol deposition to the sediment-water in terface. Esterification of sterols to pyropheophorbide-a apparently pr events the preferential removal of 4-desmethyl sterols relative to 4-m ethyl sterols, and the reduction of stenols to stanols during degradat ion. Analysis of PSEs in a gravity core covering the last 8-10 Kyr sho ws that the abundance and distribution of PSEs change with downcore va riations in sedimentology. Detailed analysis of PSEs in sediments may, therefore, provide a means to evaluate paleooceanographic changes in phytoplankton community structure and sterol early diagenesis. The syn thesis, NMR, CI-MS, and visible spectroscopic properties of four abund ant PSEs found in the Black Sea are also described.