PP11B-1780:
The Antarctic Circumpolar Current system (ACCs) is the most important current system in the Southern Ocean, characterized by strong zonal variations in specific surface water properties, variations used to classify regions whose edges are defined by fronts. The past changes in the strength and latitudinal position of the ACC frontal system are supposed to play a major role on the global oceanic circulation and thus the Earth’s climate through their impact on atmospheric CO2 contents by changes in water stratification conditions, Therefore the study of variability in the surface characteristics of the ACCs provides crucial information to understand and to reconstruct the global climate evolution. The dynamics of the upper-ocean vertical structure, primarily defined by vertical changes in salinity and temperature from the mixed layer down to the seasonal and permanent thermocline, can be tracked using the differences in stable oxygen isotopes (__18O) and Mg/Ca-based temperatures (_T) recorded in the test of planktic foraminifera. Only Mg/Ca thermometry coupled with _18O can guarantee a common source of signal, averaging the same environmental conditions (season and spatial habitat), where, the combined measurements of Mg/Ca and _18O allow to extract the _18O record of past upper ocean water, and accordingly salinity variations In this study we present paired measurements of Mg/Ca and stable oxygen isotopes of shallow-living and deeper-living planktic foraminifera preserved in core top and downcore samples from the South Pacific (36° to 45° S) retrieved during the SOPATRA cruise (South Pacific Paleoceanographic Transect) Chile-New Zealand. The total Mg/Ca values preserved in the foraminiferal calcite from 31 core top samples ranged from ~2 to 1.3 mmol/mol, allowing estimate SSTs between 16° and 12° C. Additionally, to evaluate the reliability of the Mg/Ca signal paleothermometry for long term reconstruction we determined the effect of calcite saturation state (_CO32-) into on foraminiferal Mg/Ca concentration in the different selected species. In order to track the upper water column dynamics and strength of the ACC during the last ~200 kyr, we will test our calibration on downcore records gravity cores SO213-59-2 and SO213-60-2 retrieved from the northern border of the Subantarctic Zone (SAZ) of the East Pacific Rise
