GLACIAL INTERGLACIAL CHANGES IN SEDIMENT RAIN RATE IN THE SW INDIAN SECTOR OF SUB-ANTARCTIC WATERS AS RECORDED BY TH-230, PA-231, U, AND DELTA-N-15

High-resolution records of opal, carbonate, and terrigenous fluxes hav e been obtained from a high-sedimentation rate core (MD84-527: 43-degr ees 50'S; 51-degrees 19'E; 3269 m) by normalization to Th-230. This me thod estimates paleofluxes to the seafloor on a point-by-point basis a nd distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sedi ment redistribution by bottom currents. We also measured sediment delt aN-15 to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations. Our results show that opal accumulation rates on the seafloor during the Holocene and s tage 3, based on C-14 dating, were respectively tenfold and fivefold h igher than the vertical rain rates, At this particular location, chang es in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column. Correction for syndepo sitional sediment redistribution and the improved time resolution that can be achieved by normalization to Th-230 disclose important variati ons in opal rain rates. We found relatively high but variable opal pal eoflux during stage 3, with two maxima centered at 36 and 30 kyr B.P., low opal paleoflux during stage 2 and deglaciation and a pronounced m aximum during the early Holocene, We interpret this record as reflecti ng variations in opal production rates associated with climate-induced latitudinal migration of the southern ocean frontal system. Sediments deposited during periods of high opal paleoflux also have high authig enic U concentrations, suggesting more reducing conditions in the sedi ment, and high Pa-231/Th-230 ratios, suggesting increased scavenging f rom the water column. Sediment deltaN-15 is circa 1.5 per mil higher d uring isotopic stage 2 and deglaciation. The low opal rain rates recor ded during that period appear to have been associated with increased n itrate depletion. This suggests that opal paleofluxes do not simply re flect latitudinal migration of the frontal system but also changes in the structure of the upper water column. Increased stratification duri ng isotopic stage 2 and deglaciation could have been produced by a mel twater lid, leading to lower nitrate supply rates to surface waters.