Millennial- to centennial-scale changes in sea surface temperature in the tropical South Atlantic throughout the Holocene

Abstract

We performed δ18OC (Globigerinoides ruber, 250–300μm white) and SST (modern analogue technique) paleoceanographic reconstructions for the western tropical South Atlantic Ocean at the northeast Brazilian margin to assess millennial- to centennial-scale climatic shifts that may be propagated by the thermohaline circulation. The results show a progressive SST increase (~1°C) over the Holocene, with a prominent shift occurring during the mid-Holocene that may be linked to changes in insolation distribution. Furthermore, spectral and coherency analyses reveal several centennial- to millennial-scale modes of variability that are similar in both proxy records (4.1–3.8kyr, 1.5–1.0kyr, ~700yr, 570–560yr, ~390yr, ~350yr and ~330yr). Such variability could be the result of (1) solar-induced atmospheric changes at northern high latitudes (possibly propagated southward by the meridional overturning circulation and hence inducing shifts in tropical δ18Oc and sea surface temperature), and/or (2) salinity anomalies propagated from the Southern Atlantic Ocean and transmitted to the study site through the Agulhas Leakage. These climate oscillations may have had substantive effects on the Holocene climate system, especially over the tropical western South Atlantic Ocean and the South American continent. Our data show that the western tropical South Atlantic may respond to multi-centennial to millennial oscillations that are possibly triggered by external (solar) and internal (northern and southern high latitudes) climate forcing. Further investigations are necessary to illuminate the role of the western tropical South Atlantic in inter-hemispheric heat transfer.