Millennial‐ to Orbital‐Scale Responses of Western Equatorial Atlantic Thermocline Depth to Changes in the Trade Wind System Since the Last Interglacial

Abstract

Surface ocean circulation in the western equatorial Atlantic is mainly wind driven and plays a major role for the transport of warm waters to the North Atlantic. Past changes in the strength and direction of the trade winds are well documented, but the response of the western equatorial Atlantic circulation and water column structure to these changes is unclear. Here we used the difference between the stable isotopic oxygen composition of two species of planktonic foraminifera (Globigerinoides ruber white and Neogloboquadrina dutertrei) from two sediment cores collected off northeastern Brazil to investigate millennial‐ and orbital‐scale changes in upper ocean stratification since the Last Interglacial. Our records indicate enhanced upper ocean stratification during several Heinrich stadials, partly due to a shoaling of the thermocline, which was linked to a decrease in the strength of southeast trades winds. In addition, we show that a decrease in wind zonality induced by increases in Northern Hemisphere low‐latitude summer insolation causes a shoaling of the thermocline in the western equatorial Atlantic. These ocean‐atmosphere changes contributed to a reduction in the cross‐equatorial transport of warm waters, particularly during Heinrich stadials and Marine Isotope Stage 4.

Contrasting late-glacial paleoceanographic evolution between the upper and lower continental slope of the western South Atlantic

“…(c) Mean air temperature from GeoB6211-2 (Chiessi et al, 2015). (d) Carbon dioxide (CO 2 ) concentration from Antarctic EPICA Dome C (Lüthi et al, 2008) on the Antarctic Ice Core Chronology (AICC2012) (Veres et al, 2013;Bazin et al, 2013). (e) Antarctic oxygen isotope from EDML (EPICA community members, 2004) on the AICC2012 chronology.…”

“…The records distributed along the western South Atlantic display considerably het-L. G. Luz et al: Contrasting late-glacial record across the South Atlantic Slope erogeneous features in terms of sedimentation rate and response to the adjacent continental climate, which makes the scientific outputs extremely dependent on the core site location. Those cores located adjacent to the semiarid NE Brazil allowed several investigations addressing the interplay between changes in the Atlantic Meridional Overturning Circulation (AMOC), the sea surface temperature (SST) of the tropical Atlantic, and the continental climate (in terms of precipitation and vegetation cover) in centennial to millennial timescales (Behling et al, 2000;Bouimetarhan et al, 2018;Burckel et al, 2015;Crivellari et al, 2019;Venancio et al, 2018;Zhang et al, 2015Zhang et al, , 2017. Otherwise, marine records recovered from the subtropical realm (south of 20 • S) generally do not show obvious sea surface millennial-scale features like those from NE Brazil (Santos et al, 2017a); nonetheless, this area suffers large changes in the winddriven upwelling patterns, with consequences for regional upper-ocean productivity (Lessa et al, 2019;Portilho-Ramos et al, 2019).…”

Contrasting late-glacial paleoceanographic evolution between the upper and lower continental slope of the western South Atlantic

“…Jennerjahn et al, 2004;Lessa et al, 2017;Mulitza et al, 2017;Portilho-Ramos et al, 2015;Rühlemann et al, 1999). Cores located adjacent to the semi-arid NE Brazil have allowed for several investigations addressing the interplay between changes in the Atlantic Meridional Overturning Circulation (AMOC), the sea surface temperature (SST) of the tropical Atlantic, and the continental climate (in terms of precipitation and vegetation cover) in centennial to millennial time-scales (Behling et al, 2000;Bouimetarhan et al, 2018;Burckel et al, 2015;Crivellari et al, 2019;Venancio et al, 2018;Zhang et al, 2015Zhang et al, , 2017.…”

Millennial-scale variability in eastern South American climate and western South Atlantic circulation during the last 70,000 years

“…We note that the magnitude of the modeled precipitation anomalies may depend on the strength of the AMOC perturbation. BAHR et al, 2018;DEPLAZES et al, 2013), NW (ZHANG et al, 2017) and NE (ARZ et al, 1998;JAESCHKE et al, 2007;MULITZA et al, 2017;NACE et al, 2014;VENANCIO et al, 2018) South America (Fig. 4.6a-j).…”