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Article Dans Une Revue Quaternary Science Reviews Année : 2023

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

Résumé

Paleoceanographic studies addressing the oceanographic variability in the western sector of the subtropical 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 Southwestern 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 U37K’ and isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs)-based TEX86H proxies were compared with those previously obtained from the same core via Globigerinoides ruber (G. ruber) Mg/Ca and planktonic foraminifera Modern Analog Technique (MAT).The temporal variations of the temperature estimates derived from the U37K' and TEX86H indexes showed similar patterns, even though the absolute U37K' temperatures were systematically lower than those derived from TEX86H. Such a difference was related to the different habitat depths of alkenones and isoGDGTs source organisms of – haptophyte algae and marine Thaumarchaeota, respectively. The temperature estimates from TEX86H 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 U37K' were close to the MAT values at between 0 and 100 m and to those derived from TEX86H5 between 0 and 200 m depth, demonstrating that the U37K' proxy recorded temperatures from the upper thermocline. During MIS 5e, the difference in temperature estimates from TEX86H and U37K' 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 intensification 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 TEX86H and U37K' is a promising approach to estimating paleoceanographic changes in the upper thermocline.
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Dates et versions

hal-04150017 , version 1 (10-10-2023)

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Joana Cruz, Ioanna Bouloubassi, Arnaud Huguet, Alice M.S. Rodrigues, Thiago Santos, et al.. Multiproxy reconstruction of late quaternary upper ocean temperature in the subtropical southwestern Atlantic. Quaternary Science Reviews, 2023, 307, pp.108044. ⟨10.1016/j.quascirev.2023.108044⟩. ⟨hal-04150017⟩
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