Thermal evolution of the western South Atlantic and the adjacent continent during Termination 1

Abstract

Abstract. During Termination 1, millennial-scale weakening events of the Atlantic meridional overturning circulation (AMOC) supposedly produced major changes in sea surface temperatures (SSTs) of the western South Atlantic, and in mean air temperatures (MATs) over southeastern South America. It has been suggested, for instance, that the Brazil Current (BC) would strengthen (weaken) and the North Brazil Current (NBC) would weaken (strengthen) during slowdown (speed-up) events of the AMOC. This antiphase pattern was claimed to be a necessary response to the decreased North Atlantic heat piracy during periods of weak AMOC. However, the thermal evolution of the western South Atlantic and the adjacent continent is so far largely unknown. Here we address this issue, presenting high-temporal-resolution SST and MAT records from the BC and southeastern South America, respectively. We identify a warming in the western South Atlantic during Heinrich Stadial 1 (HS1), which is followed first by a drop and then by increasing temperatures during the Bølling-Allerød, in phase with an existing SST record from the NBC. Additionally, a similar SST evolution is shown by a southernmost eastern South Atlantic record, suggesting a South Atlantic-wide pattern in SST evolution during most of Termination 1. Over southeastern South America, our MAT record shows a twostep increase during Termination 1, synchronous with atmospheric CO 2 rise (i.e., during the second half of HS1 and during the Younger Dryas), and lagging abrupt SST changes by several thousand years. This delay corroborates the notion that the long duration of HS1 was fundamental in driving the Earth out of the last glacial.

Productivity Evolution in the South Brazilian Bight During the Last 40,000 Years

“…Considering the age uncertainties, the most conspicuous change observed over the YD was a pronounced salinity decrease (Figure c). That finding is also in line with other records from the western subtropical South Atlantic showing diminished salinity both northward (25°S) (Pivel et al, ) and further south (32°S) to our study area (Chiessi et al, ) during the YD. It is likely that shifts in the interhemispheric export of salt throughout the last deglaciation (Chiessi et al, ; Pivel et al, ) fueling the AMOC recovery toward the Holocene (Figure j) would have strongly contributed to such anomalous salinity decrease recorded along the YD.…”

“…The currents are labeled as AC‐Agulhas Current, ACC‐Antarctic Circumpolar Current, BC‐Brazil Current, BCC‐Brazilian Coastal Current, BGC‐Benguela Current, MC‐Malvinas Current, SAC‐South Atlantic Current, SEC‐South Equatorial Current. The location of the marine sediment core investigated in this study, as well as of some archives discussed here are shown: (1) GeoB2107‐3 (this study), (2) GL‐1090 (Lessa et al, ), (3) BCCF06‐03 (Souto et al, ), (4) GL‐74 (Portilho‐Ramos et al, ), (5) GeoB6211‐2 (Chiessi et al, ), and (6) Botuverá Cave (Wang et al, ). The satellite images show the core site location (black and white circle) and the mesoscale surface circulation off Cape Santa Marta (CSM), defined by the meandering flow of the Brazil Current (BC): (b) the infrared satellite image (AVHRR/NOAA) depicts the development of the Santa Marta cyclonic vortex delineated by a thermal contrast in °C (color shading) between the BC and the Brazilian Coastal Current (BCC); (c) the ocean color satellite image (VIIRS‐SNPP/NOAA) depicts the development of Santa Marta cyclonic vortex delineated by the surface chlorophyll a concentration in mg/m 3 (color shading) mirroring phytoplankton bloom and primary productivity.…”

“…Thus, our MAT‐derived proxy for temperature may not have been sensitive enough to capture the rather subtle changes in the upper water column. Strong SST increases though have been reported for HS1 in planktonic foraminiferal Mg/Ca records of the western (Chiessi et al, ) and eastern (Barker et al, ) subtropical South Atlantic. Yet, millennial‐scale changes of temperature in the upper subtropical western South Atlantic during other HS events would likely have played only a marginal role along the last glacial cycle (Santos et al, ).…”

“…Apart from the impact on stratification, changes induced by the BC cyclonic vortices would also embody shifts in seawater temperature. During events of weakened AMOC and impaired northward transport of heat, intensified BC would redirect southward the excess of heat (Chiessi et al, ), which would be mostly stored at intermediate depths (Dahl et al, ; Weber et al, ). Instead, changes of temperature in periods of strengthened BC fostering upwelling and the seaward inflow of cold nutrient‐rich waters would produce cooling at (sub) surface levels.…”

“…0.3‰ for δ 18 O ivc‐ssw (Mohtadi et al, ). Higher δ 18 O ivc‐ssw values indicate enhanced sea surface salinity (Chiessi et al, ).…”