The last deglaciation: timing the bipolar seesaw

J B Pedro,V Masson-Delmotte,S O Rasmussen,A D Moy,J Chappellaz,V I Morgan,T D Van Ommen,M Delmotte

doi:10.5194/cp-7-671-2011

Abstract

Abstract. Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

Highlights

The last deglaciation (ca. 19 to 11 thousand years before present, where present is defined as 1950) is the most recent example of a major naturally forced global climate change
Antarctica first warmed during the glacial conditions of Greenland stadial 2 (GS-2), cooled during the Antarctic Cold Reversal (ACR), as Greenland experienced the warmth of the BøllingAllerød interstadial (B-A or GI-1a-e)
All records show a similar pattern: an overall warming trend interrupted by the millennial scale ACR

Summary

Introduction

The last deglaciation (ca. 19 to 11 thousand years before present (ka BP), where present is defined as 1950) is the most recent example of a major naturally forced global climate change. Previous studies confirm opposing climate trends on millennial timescales between the northern and southern mid to high-latitudes during this interval Antarctica first warmed during the glacial conditions of Greenland stadial 2 (GS-2), cooled during the Antarctic Cold Reversal (ACR), as Greenland experienced the warmth of the BøllingAllerød interstadial (B-A or GI-1a-e). The conventional explanation for these opposing climate trends is the bipolar ocean seesaw; it proposes that the two hemispheres are coupled via oscillations in the dominant direction of heat transport in the Atlantic Ocean due to perturbations in the meridional overturning circulation (Broecker, 1998). An alternate (though potentially complimentary) mechanism has been put forward that invokes atmospheric teleconnections in forcing the bipolar coupling (Anderson et al, 2009 and references therein). A key role of the palaeoclimate record is to provide firm observational constraints against which these dynamical mechanisms and their timescales can be tested

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Results

Conclusion