Prolonged warming of the Brazil Current precedes deglaciations

Author(s):Show less -

Santos, Thiago P. ; Lessa, Douglas O. ; Venancio, Igor M. ; Chiessi, Cristiano M. ; Mulitza, Stefan ; Kuhnert, Henning ; Govin, Aline ; Machado, Thiago ; Costa, Karen B. ; Toledo, Felipe ; Dias, Bruna B. ; Albuquerque, Ana Luiza S.

• Document type: Journal article
• Source: Earth and Planetary Science Letters; v. 463, p. 1-12, APR 1 2017.
• Web of Science Citations: 17

Abstract

Paleoceanographic reconstructions from the Brazil Current are scarce and lack the required temporal resolution to appropriately represent its variability during key periods of the last glacial-interglacial cycles. Here, we present the first high-temporal resolution multiproxy reconstruction of the Brazil Current at 24 degrees S covering the last 185ka. During the last and penultimate glacial periods, our Mg/Ca-derived sea surface temperature (SST) record shows a strong cooling at ca. 47 and ca. 156ka, respectively, that is followed by a warming trend from late-Marine Isotope Stage (MIS) 3 to MIS1 and from late-MIS6 to MIS5e, respectively. Importantly, the Brazil Current warmed uninterruptedly towards Termination I (II) after the low SST at ca. 47 and ca. 156ka, with no SST minima during the Last Glacial Maximum or penultimate glacial maximum. The reason for the strong cooling and the warming trend during late-MIS 3 and late-MIS 6 could reside in the favorable obliquity configuration. However, this mechanism is not sufficient to sustain the warming observed for the rest of the last and penultimate glacial periods. We propose that the change in the Atlantic meridional overturning circulation (AMOC), as described in the literature, from a ``warm{''} to a ``cold mode{''} for MIS2 and MIS6 is responsible for the accumulation of warm waters in the subtropical western South Atlantic, preventing SST minima during the last and penultimate glacial maxima in the region. Change in benthic delta C-13 corroborates that a fundamental modification in the AMOC mode might have triggered the heat accumulation. Our data also show a sudden increase in SST and surface salinity during the last glacial descent (MIS 4), indicating that the western portion of the subtropical gyres may have acted as a heat and salt reservoir, while higher latitude climates transited to a glacial background. Our findings imply that the AMOC ``cold mode{''} induces heat storage in the subtropical western South Atlantic and, because of that, the last two regional SST minima occurred out-of-phase with the glacial maxima of higher latitudes. (C) 2017 Elsevier B. V. All rights reserved. (AU)

• FAPESP's process: 12/17517-3 - Response of the Western Atlantic Ocean to changes in the Atlantic meridional overturning circulation: from millennial to seasonal variability
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: Research Program on Global Climate Change - Young Investigators