Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination

Siwan M Davies ,Christopher J Fogwill ,T D Van Ommen,Michael E Weber ,Laurie Menviel ,Helen Millman ,Camilla M Rootes ,Mauro Rubino ,Nicholas R Golledge ,Chris S M Turney ,D Thornton ,Alan Cooper ,Andrés Rivera ,J Vohra,Mark A J Curran ,Niels C Munksgaard ,Andrew D Moy ,John Woodward ,Michael I Bird ,Kate Winter ,Andy Baker ,Bethany Ellis ,D M Etheridge

doi:10.1038/srep39979

Abstract

Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000–11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved ‘horizontal ice core’ from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600–12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise.

Highlights

The end of the twenty-first century[3]
We take a novel approach that investigates a new 800 m long ‘horizontal ice core’ that captures a unique record of ice-sheet dynamics and climate across the Weddell Sea Embayment (WSE)[19], a region which today drains more than one-fifth of the ice-mass of continental Antarctica, including sectors of the East and West Antarctic ice sheets and the Antarctic Peninsula (Fig. 1A)
Our modelling, together with the results of previous studies[2,13,18], suggests that a significant fresh water input into the Southern Ocean provides a potential trigger for the ACR signal, a hypothesis supported by our field data

Summary

Introduction

The end of the twenty-first century[3] These projections, do not fully include ice-sheet-ocean dynamic feedbacks which are believed to have triggered rapid continental ice-sheet retreat and driven periods of abrupt sea-level rise during the geological past[2,8]. Within the ACR, Meltwater Pulse 1A (MWP-1A) forms a prominent abrupt rise in sea level of ~16 m (14,700–14,300 years or 14.7–14.3 ka) that has been a major focus of previous studies, and which was coincident with a period of enhanced iceberg flux in the Southern Ocean[2]. An improved understanding of the links between AIS stability and ice-ocean-climate feedbacks throughout the LGT (i.e. not just MWP-1A), and its relationship to Northern Hemisphere changes, is critical for improving projections of sea-level rise[3,4] and understanding ice-sheet-climate feedbacks[2,17] in detail. We take a novel approach that investigates a new 800 m long ‘horizontal ice core’ that captures a unique record of ice-sheet dynamics and climate across the Weddell Sea Embayment (WSE)[19], a region which today drains more than one-fifth of the ice-mass of continental Antarctica, including sectors of the East and West Antarctic ice sheets and the Antarctic Peninsula (Fig. 1A)

Methods

Results

Conclusion