Southern Ocean convection amplified past Antarctic warming and atmospheric CO2 rise during Heinrich Stadial 4

Luke Skinner,Laurie Menviel,Julia Gottschalk,Mervyn Greaves,Lauren Broadfield

doi:10.1038/s43247-020-00024-3

Abstract

The record of past climate highlights recurrent and intense millennial anomalies, characterised by a distinct pattern of inter-polar temperature change, termed the ‘thermal bipolar seesaw’, which is widely believed to arise from rapid changes in the Atlantic overturning circulation. By forcing a suppression of North Atlantic convection, models have been able to reproduce many of the general features of the thermal bipolar seesaw; however, they typically fail to capture the full magnitude of temperature change reconstructed using polar ice cores from both hemispheres. Here we use deep-water temperature reconstructions, combined with parallel oxygenation and radiocarbon ventilation records, to demonstrate the occurrence of enhanced deep convection in the Southern Ocean across the particularly intense millennial climate anomaly, Heinrich Stadial 4. Our results underline the important role of Southern Ocean convection as a potential amplifier of Antarctic warming, and atmospheric CO2 rise, that is responsive to triggers originating in the North Atlantic.

Highlights

The record of past climate highlights recurrent and intense millennial anomalies, characterised by a distinct pattern of inter-polar temperature change, termed the ‘thermal bipolar seesaw’, which is widely believed to arise from rapid changes in the Atlantic overturning circulation
Over at least the last 800,000 years, millennial climate variability has been characterised by a distinct pattern of inter-hemispheric temperature change, accompanied by changes in the cryosphere and the global biogeochemical and hydrological cycles
A handful of records that capture centennial-millennial-scale deep-water temperature changes associated with e.g. Dansgaard–Oeschger (D–O) climate variability currently exist, e.g.15–19, and it remains to be shown that such signals can be reproduced by parallel measurements in multiple benthic foraminifer species

Summary

Introduction

The record of past climate highlights recurrent and intense millennial anomalies, characterised by a distinct pattern of inter-polar temperature change, termed the ‘thermal bipolar seesaw’, which is widely believed to arise from rapid changes in the Atlantic overturning circulation. Over at least the last 800,000 years, millennial climate variability has been characterised by a distinct pattern of inter-hemispheric temperature change, accompanied by changes in the cryosphere and the global biogeochemical and hydrological cycles This dominant mode of ‘rapid’ climate variability has been described conceptually in terms of a ‘thermal bipolar seesaw’[1,2], whereby gradually rising temperatures over Antarctica represent a ‘convolution’ of their more abrupt. Note that the thermal bipolar seesaw is defined here as a pattern of inter-hemispheric temperature change, rather than a hypothetical mechanism According to this conceptual model, Antarctica takes a few centuries to respond to the initiation of a seesaw event, upon which it gradually catches up with the inverse of Greenland temperature change Our results reveal the ‘fingerprint’ of enhanced heat- and gas exchange in the deep Southern Ocean, in parallel with rising Antarctic temperature and atmospheric CO2, as observed in numerical model simulations where enhanced Southern Ocean convection actively contributes to an increase in both Antarctic temperature and atmospheric CO2 concentration

Methods

Results

Conclusion