Glacial–interglacial interplay of southern- and northern-origin deep waters in the São Paulo Plateau – Vema Channel area of the western South Atlantic

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system due to its role in oceanic heat transport, CO2 exchange between the ocean and atmosphere, and carbon storage in the ocean interior. Previous studies have proposed dramatic changes in the global thermohaline circulation during glacial–interglacial cycles. Here, we present isotopic, geochemical and foraminiferal records from the core AI-3152 (water depth 3435 m). These data demonstrate shifts in the depth of northern- and southern-sourced deep water masses, as well as of foraminiferal lysocline in the São Paulo Plateau area, north-westward of the Vema Channel, in the western South Atlantic over the last 167 kyr. That the study area was bathed by southern-origin deep water masses during MIS 6, 4–2 and MIS 5.4–5.1, whereas a prevalence of northern-sourced waters is reconstructed for interglacials and MIS 5.5 and 1. Our data suggest that a carbonate saturation state associated with deep water ventilation, Antarctic air temperatures, ocean–atmosphere gas exchange, Southern Ocean upwelling rates and likely productivity changes significantly affected the deep sea oceanographic conditions in the São Paulo Plateau area during glacials and MIS 5.4–5.1. A comparison of δ18OCw and δ13СCw recorded from core AI-3152 to other stable isotope records from the Rio Grande Rise, to the east of the Vema Channel clearly indicated the presence of a southern-derived analogue of dense Weddell Sea Deep Water at 3.4–4 km depth in the Vema Channel area during the MIS 3–2 interval. An approximately 500 m steeper W-E slope on the boundary of two southern-origin deep water masses was inferred on both sides of the Vema Channel during MIS 3–2. This boundary shift likely reflects a northward expansion of the densest water mass in the Atlantic, thereby impacting geostrophic balance.