Last Interglacial (MIS5) sea surface temperaturas in the Brazil-Malvinas Confluence Zone off northern Argentina

NATALIA GARCÍA CHAPORI; CECILIA LAPRIDA; CRISTIANO CHIESSI; ROBERTO A. VIOLANTE; TORSTEN BICKERT

Cancun

Congreso; Meeting of the Americas; 2013

The South Atlantic is a region of crucial water exchange between the Southern Ocean and thesubtropical basins. The area off northern Argentina, constitutes a key location due to theconvergence of the Brazil and Malvinas Currents: the Brazil‐Malvinas Confluence Zone (BMCZ),one of the most energetic regions of the World Ocean. Sediment core GeoB2806‐4 (3500m waterdepth, 38°S‐53°W) was analyzed in order to reconstruct the upper water column hydrographyduring the Last Interglacial. The site is located in the core of the BMCZ, on the Necochea Terrace at the lower slope off Argentine. Biostratigraphy based on planktic foraminifera and δ18O analysesperformed on U. peregrina indicate that the analyzed core section was deposited during theMiddle‐Late Pleistocene, including Termination II (TII) and OIE 5.4 to OIE 5.03, during the LastInterglacial. OIE 5.5 could not be identified probably due to methodological constrains related withsampling strategy. Planktic foraminiferal assemblages were analyzed for quantitative sea surfacetemperature (SST) reconstruction using the Modern Analog Technique (MAT) and TransferFunction (TF). Modern SSTs were extracted from the World Ocean Atlas 2009 (WOA09) forcomparison. During TII, summer SSTs were from ~11.8°C to 17°C (MAT) and ~10°C to 16.6°C (TF), and oscillated between ~13°C and 18.7°C, and 13.3°C and 20.4°C for OIEs 5.4‐5.03, respectively. Winter SSTs varied from ~7.5°C to 11.5°C (MAT) and from ~5.8°C to 10.6°C (TF) for TII, and oscillated between ~8°C and 13.4°C, and 9°C and 16.9°C for OIEs 5.4 ‐ 5.03, respectively. Considering both techniques, TF? SSTs seem to be more reliable than the values obtained by MAT. Reconstructions would indicate that during OIE 5.4 to 5.03 the Southwestern South Atlantic SSTs were similar or slightly colder than modern ones, but slightly warmer than TII. Our results differ from earlier reconstructions of the CLIMAP Group for the Last Interglacial, who recognized warmer SSTs (summer SST ~18‐20°C and winter SST ~14‐16°C) for the Subtropical Gyre of the South Atlantic. However, they are coincident with SST trends from cores collected off southern Brazil, which indicate an increase of 2‐3°C in the SST for the MIS6‐MIS5 transition, and small positive anomalies (lower than 1°C) obtained for the studied area for the Last Interglacial by oGCMs.