Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials

Abstract

Subtropical ocean gyres play a key role in modulating the global climate system redistributing energy between low and high latitudes. A poleward displacement of the subtropical gyres has been observed over the last decades, but the lack of long-term monitoring data hinders an in-depth understanding of their dynamics. Paleoceanographic records offer the opportunity to identify meridional changes in the subtropical gyres and investigate their consequences to the climate system. Here we use the abundance of planktonic foraminiferal species Globorotalia truncatulinodes from a sediment core collected at the northernmost boundary of the South Atlantic Subtropical Gyre (SASG) together with a previously published record of the same species from the southernmost boundary of the SASG to reconstruct meridional fluctuations of the SASG over last ca. 70 kyr. Our findings indicate southward displacements of the SASG during Heinrich Stadials (HS) 6-4 and HS1, and a contraction of the SASG during HS3 and HS2. During HS6-4 and HS1, the SASG southward displacements likely boosted the transfer of heat to the Southern Ocean, ultimately strengthening deep-water upwelling and CO2 release to the atmosphere. We hypothesize that the ongoing SASG poleward displacement may further increase oceanic CO2 release.

Surface fertilisation and organic matter delivery enhanced carbonate dissolution in the western South Atlantic

“…As the upwelling of subsurface waters necessarily implies a break in the upper water column stratification, we should also expect a similar behaviour in the stratification proxies. This can be primarily confirmed by the high relative abundances of G. truncatulinoides right coiling form, which also point to a less stratified, well-mixed upper water column during MIS 4 (Figure 2D, Lohmann and Schweitzer, 1990;Renaud and Schmidt, 2003;Feldmeijer et al, 2015;Billups et al, 2016;Pinho et al, 2021). Furthermore, G. truncatulinoides types II and V (right coiling forms) have also been associated with a shallow thermocline and eutrophic conditions (de Vargas et al, 2001;Ujiiéand Lipps, 2009;Ujiiéet al, 2010;Quilleveŕéet al, 2013).…”

Antarctic evidence for an abrupt northward shift of the Southern Hemisphere westerlies at 32 ka BP

“…Additional evidence comes from the reconstruction of the latitudinal position of the South Atlantic Subtropical Gyre (SASG) which suggests that the gyre was displaced northwards from at least 30 ka BP. This includes during Heinrich stadials 3 and 2, when the gyre is typically expected to shift poleward 52 . The latitudinal position of SASG is governed by the position of oceanic fronts namingly Subtropical, Subantarctic, and Polar Front 52 .…”

“…This includes during Heinrich stadials 3 and 2, when the gyre is typically expected to shift poleward 52 . The latitudinal position of SASG is governed by the position of oceanic fronts namingly Subtropical, Subantarctic, and Polar Front 52 . In turn, the position of oceanic fronts is known to be sensitive to the latitudinal position of SHWW 53 .…”

>b<Paleoprodutividade dos cocolitoforídeos no Atlântico Sudoeste nos últimos 700 mil anos e sua relação com os ciclos biogeoquímicos:>/b< evidências a partir da Sr/Ca nos cocólitos

“…(Baumann et al, 1999, Leonhardt et al, 2013, Santos et al, 2017. Também é documentado o deslocamento para sul do giro subtropical durante períodos climáticos mais frios (Pinho et al, 2021).…”