Millennial Scale Events Of The Last 40 Ky In The South Atlantic: From The Tropics To The Subantarctic

Abstract:

We present sub-millennially resolved time series from core MD08-3167, retrieved at 23°S and 1950 m water depth on the Namibian margin during 2008 RETRO cruise. At present, this region is characterised by upwelling of waters from 150-500 m depth. Stable isotopes (d¹⁸O and d¹³C) and Mg/Ca were measured on the planktonic foraminifer Globigerina bulloides, which may be assumed to thrive in upwelled waters. Stable isotopes were also measured on the benthic foraminifer Cibicides wuellerstorfi. Core MD08-3167 records were dated based on 23 ¹⁴C dates covering the last 30 ky. These records are compared with new and published surface and deep water records from cores from the North-East Brazil margin (MD09-3257, 4.3°S, 2340 m, and MD09-3256Q, 3.33°S, 3537 m; Burckel et al., 2015) and the South Atlantic (core MD07-3076Q, 44°S, 3770 m; Gottschalk et al., 2015).

Our comparison of surface records indicates that sea surface temperature increases, in phase with Antarctic warming during the Younger Dryas (YD), Heinrich Stadial (HS) 1 and HS4, took place everywhere in the South Atlantic, form equatorial Brazil to the Subantarctic region. In addition, the planktonic d¹⁸O records from the Namibian margin indicate that rapid changes in surface ocean circulation and upwelling intensity took place in that region at the beginning of HS1, possibly in response to sea-ice retreat around Antarctica and/or changes in the intensity or position of the westerlies.

The deep water records show that water mass ventilation during the YD and Heinrich stadials in the South Atlantic was very similar between 1800 and 2900 m, but a chemical divide seems to be present below this depth before HS1. The comparison of these records demonstrates that the large ocean circulation changes observed during the YD and HS1 (e.g., Waelbroeck et al., 2011) also prevailed during preceding Heinrich stadials and are thus not characteristic of terminations.