LATE QUATERNARY CLIMATE-CHANGE FROM DELTA-O-18 RECORDS OF MULTIPLE SPECIES OF PLANKTONIC-FORAMINIFERA - HIGH-RESOLUTION RECORDS FROM THE ANOXIC CARIACO BASIN, VENEZUELA

Seasonal trade wind-induced upwelling along the southern margin of the Caribbean Sea occurs in response to the annual migration of the Inter tropical Convergence Zone. Laminated, high deposition rate sediments o f the Cariaco Basin, a small anoxic basin on the Venezuelan continenta l shelf, clearly record large changes in the past intensity of this up welling. Because sediments of the Cariaco Basin are largely unbioturba ted, they offer a natural opportunity to study the stable isotopic rec ords of multiple planktonic foraminiferal taxa and to evaluate their s ensitivity to both the modern hydrography and temporal changes in upwe lling intensity and climate. Oxygen isotope data (delta(18)O) from fou r dominant foraminiferal taxa are presented for the time period coveri ng the last 28 kyr. The delta(18)O data from Globigerina bulloides, af ter correction for nonequilibrium precipitation, are used as a monitor of sea surface conditions during the winter-spring upwelling season. The delta(18)O data from white Globigerinoides ruber are used as a mea sure of annual-average conditions in the near surface, while pink G. r uber data are consistent with use as an index of end-member conditions during the summer-fall nonupwelling season. Data from the deeper dwel ling Neogloboquadrina dutertrei yield information on conditions near t he base of the local thermocline. During the last glacial, delta(18)O data from G. ruber and generally reduced interspecific differences ind icate cooling of surface waters over the Cariaco Basin by up to 4 degr ees C. This longer-term cooling does not appear to be related to chang es in upwelling intensity along the coast but may instead reflect more regional cooling of the larger Caribbean. Superimposed on this patter n, between 12.6 and similar to 10 ka, is a convergence of delta(18)O d ata between G. bulloides and N. dutertrei, implying much stronger upwe lling during the last deglaciation. This scenario is consistent with o ther evidence for high productivity at this time. At similar to 14 ka, a sharp delta(18)O depletion event observed in all taxa seems to have been produced by increased freshwater discharge to the southern Carib bean, suggesting either higher regional rainfall or the influence of g lacial melting in the Andes. Minimum delta(18)O values of pink G. rube r around 6-7 ka record warmer summer sea surface temperatures and/or d ecreased salinity in the mid-Holocene.