Tropical climate variability in the Cariaco Basin,Venezuela during marine isotope stage 3: A multi proxy approach.

摘要

We use a multi-proxy approach to marine sediments from the Cariaco Basin to reconstruct the paleoceanographic and paleoclimatic conditions on a decadal-centennial timescale during 10 interstadial-stadial cycles, including Heinrich events 4 and 5, that punctuate Marine Isotope Stage 3 (MIS-3, ∼32-55ka). We evaluate the timing and magnitude of millennial scale climate variability in the tropics relative to changes in high latitude regions to determine what role, if any, the tropics play in driving global climate change.;The modern salinity:oxygen isotopic composition of seawater (delta 18Ow) relationship is determined and used in conjunction with paleotemperature estimates to determine past sea surface salinity (SSS) changes. The modern salinity:delta18Ow relationship displays significant intra-seasonal variability which is attributed to seasonal changes in freshwater input from the local rivers in this region. The data also show distinct seasonal mixing lines that define the upwelling and non-upwelling regimes. Comparing estimated salinities, using the planktonic foraminifera delta18Oc collected in sediment trap samples, to in situ salinity measurements favors the the paleosalinity equation generated during the upwelling season for paleoclimate reconstructions.;Paired oxygen isotope and Mg/Ca records for planktonic foraminifera Globigerinoides ruber from sediment core MD03-2621 were used to reconstruct sea surface temperature (SST), delta18Ow, and SSS variations for the last glacial period. Mean Mg/Ca derived SST estimates an increase of ∼3-4°C at stadial-interstadial transitions. Based on our SST and SSS records we propose a model in which changes in the tropics serve as a trigger for Heinrich events.;Decadal scale records of sediment color reflectance, and planktonic foraminiferal shell weight and carbon isotope variability for Globigerina bulloides and Globigerinoides ruber is presented. Sediment trap results from the Cariaco Basin suggest that the shell weight variability is driven, in part, by changes in the surface water carbonate ion concentration [CO3=]. Using the modern relationship between shell weight and [CO3=] for this area, we estimate down-core [CO3=] variability to infer changes in surface water partial pressure of carbon dioxide (pCO 2). We conclude that the Cariaco Basin was a greater source for atmospheric carbon dioxide during this time interval than today with interstadial pCO2 values higher than those estimated for stadials.