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

C M Chiessi,G Mollenhauer,M Prange,J Groeneveld,S Mulitza,J B Silva

doi:10.5194/cp-11-915-2015

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 anti-phase 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 two-step increase during Termination 1, synchronous with atmospheric CO2 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.

Highlights

The thermal bipolar seesaw describes the warming occurring in the Southern Hemisphere due to diminished northward heat transport within the Atlantic Ocean when the Atlantic meridional overturning circulation (AMOC) is weakened (Mix et al, 1986; Stocker, 1998)
Sedimentation rates of the investigated section of core GeoB6211-2 show a two-step decrease from the Last Glacial Maximum (LGM) to the early Holocene (Fig. 3)
The two major decreases in sedimentation rates found in GeoB6211-2 are remarkably synchronous with outstanding events of sea-level rise related to meltwater pulses that occurred at ca. 19 and 14.6 cal ka BP (Deschamps et al, 2012; Yokoyama et al, 2000)

Summary

Introduction

The thermal bipolar seesaw describes the warming occurring in the Southern Hemisphere due to diminished northward heat transport within the Atlantic Ocean when the Atlantic meridional overturning circulation (AMOC) is weakened (Mix et al, 1986; Stocker, 1998). This mechanism is efficient for perturbations of the AMOC through positive anomalous freshwater fluxes in the high latitudes of the North Atlantic (Crowley, 1992; Manabe and Stouffer, 1988). The lack of high-temporal-resolution records from the BC (Clark et al, 2012), for instance, hinders the evaluation of the previously hypothesized anti-phase behavior between the BC and the North Brazil Current (NBC) during periods of a stalled AMOC (Arz et al, 1999; Schmidt et al, 2012; Chiang et al, 2008)

Methods

Results

Discussion

Conclusion