Multiproxy reconstruction of late quaternary upper ocean temperature in the subtropical southwestern Atlantic

Paleoceanographic studies addressing the oceanographic variability in the western sector of the sub-tropical South Atlantic -especially those focused on the Brazil Current (BC) and on a time scale that reaches marine isotope stage (MIS) 5 -are still rare when compared with equivalent studies carried out in the Northern Hemisphere. In order to close the data gap prior to the last 75 ka, in an unprecedented approach in this region, we reconstructed the upper temperature variations in the Subtropical South-western Atlantic (SSWA) between late MIS 6 and the onset of MIS 4 from organic proxies, using a marine sediment core (GL-1090). Sea temperature records derived from alkenone-based UK' 37 and isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs)-based TEXH86 proxies were compared with those previ-ously obtained from the same core via Globigerinoides ruber (G. ruber) Mg/Ca and planktonic forami-nifera Modern Analog Technique (MAT). The temporal variations of the temperature estimates derived from the UK0 37 and TEXH86 indexes showed similar patterns, even though the absolute UK0 37 temperatures were systematically lower than those derived from TEXH86. Such a difference was related to the different habitat depths of alkenones and isoGDGTs source organisms of e haptophyte algae and marine Thau-marchaeota, respectively. The temperature estimates from TEXH86 match the range of Mg/Ca and MAT -derived temperatures between 0 and 10 m depth, suggesting that these proxies reflect mixed layer temperatures. In contrast, the temperature estimates derived from UK037 were close to the MAT values at between 0 and 100 m and to those derived from TEXH86 between 0 and 200 m depth, demonstrating that the UK0 37 proxy recorded temperatures from the upper thermocline. During MIS 5e, the difference in temperature estimates from TEXH86 and UK0 37 was reduced due to more prominent warming, probably related to a change in the thermal structure of the photic zone. Comparison of our data with studies of intensity and salinity anomalies of the Agulhas Current indicates a connection between the intensifi-cation of the Agulhas Leakage and the heat storage in the upper thermocline in the SSWA during MIS 5e. Our data suggest that the joint use of TEXH86 and UK0 37 is a promising approach to estimating paleo-ceanographic changes in the upper thermocline. (c) 2023 Elsevier Ltd. All rights reserved.