A HIGH-RESOLUTION RECORD OF LATE QUATERNARY UPWELLING ALONG THE OMAN MARGIN, ARABIAN-SEA BASED ON PLANKTONIC-FORAMINIFERA

Planktonic foraminiferal abundances, fluxes, test sizes, and coiling p roperties are influenced in various ways by the southwest monsoon wind s and associated upwelling in the western Arabian Sea. To determine th e short-term changes in the southwest monsoon, we have carried out a h igh-resolution time-series analysis of three upwelling indices (total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species Globigerina bulloides) from O cean Drilling Program (ODP) Site 723A (Oman Margin, western Arabian Se a) spanning the last 19 kyr. In addition, we have determined the relat ionships between upwelling intensity and the relative abundance, fluxe s, and shell concentrations of various planktonic foraminiferal specie s. Upwelling indices suggest that from 19 to 16 ka (22 to 18.2 cal kyr B.P.) the SW monsoon was relatively strong compared to the period 15. 8 to 12.5 ka (17.8 to 13.8 cal kyr B.P.). The intensification of the S W monsoon took place at 12 ka (13.1 cal kyr B.P.) and reached a peak b etween 10 and 5 ka (10.6 and 4.8 cal kyr B.P.). The high-resolution da ta further demonstrate that the SW monsoon has started weakening from 5 ka (4.8 cal kyr B.P.) and the weakest phase was in place at 3.5 ka ( 3 cal kyr B.P.), which coincides with evidence of an arid climate in w estern Tibet. Fluxes and shell concentrations of many of the planktoni c foraminiferal species increased between 12 and 5 ka in response to t he intensification of the SW monsoon winds after the last glacial peri od. Globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling. The other species whose flux es are influenced by this upwelling change are (in order from stronges t to weakest response) Globigerinita glutinata, Globigerinoides ruber, Neogloboquadrina dutertrei, Globigerinella aequilateralis, Globigerin a falconensis, and Globigerinoides sacculifer. The relative abundances of C. bulloides and G. ruber increased during intense upwelling, wher eas the relative abundances of G. glutinata, N. dutertrei, G. falconen sis, and G. sacculifer did not increase during this period, which migh t be due to differences in the productivity of various species in rela tion to upwelling change. Therefore the fluxes and shell concentration s provide better and more reliable information about the changes in th e monsoon system in the Arabian Sea than relative abundance data.