Impact of millennial-scale oceanic variability on the Greenland ice-sheet evolution throughout the last glacial period

Ilaria Tabone,Marisa Montoya,Alexander Robinson,Jorge Alvarez-Solas

doi:10.5194/cp-15-593-2019

Abstract

Abstract. Temperature reconstructions from Greenland ice-sheet (GrIS) ice cores indicate the occurrence of more than 20 abrupt warmings during the last glacial period (LGP) known as Dansgaard-Oeschger (D-O) events. Although their ultimate cause is still debated, evidence from both proxy data and modelling studies robustly links these to reorganisations of the Atlantic Meridional Overturning Circulation (AMOC). During the LGP, the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes than in the present. Therefore oceanic temperature fluctuations on millennial timescales could have had a non-negligible impact on the GrIS. Here we assess the effect of millennial-scale oceanic variability on the GrIS evolution from the last interglacial to the present day. To do so, we use a three-dimensional hybrid ice-sheet–shelf model forced by subsurface oceanic temperature fluctuations, assumed to increase during D-O stadials and decrease during D-O interstadials. Since in our model the atmospheric forcing follows orbital variations only, the increase in total melting at millennial timescales is a direct result of an increase in basal melting. We show that the GrIS evolution during the LGP could have been strongly influenced by oceanic changes on millennial timescales, leading to oceanically induced ice-volume contributions above 1 m sea level equivalent (SLE). Also, our results suggest that the increased flux of GrIS icebergs as inferred from North Atlantic proxy records could have been triggered, or intensified, by peaks in melting at the base of the ice shelves resulting from increasing subsurface oceanic temperatures during D-O stadials. Several regions across the GrIS could thus have been responsible for ice mass discharge during D-O events, opening the possibility of a non-negligible role of the GrIS in oceanic reorganisations throughout the LGP.

Highlights

Ice cores from the Greenland ice sheet (GrIS) indicate that the climate of Greenland experienced multiple abrupt temperature increases during the last glacial period (LGP) known as Dansgaard-Oeschger (D-O) events (Dansgaard et al, 1993)
Isolated peaks in volume anomalies do not necessarily imply a high millennialscale ice-volume variation over the whole LGP since they may result from sparse melting peaks, and the contribution of the oceanic variability to ice-volume changes needs to be quantified for the entire time series
This can be done by calculating the root mean square deviation of the ice-volume (V ) residuals between TOT and ORB averaged in time for each simulation of the large ensemble (LE) (m sea level equivalent (SLE)) as εV =

Summary

Introduction

Ice cores from the Greenland ice sheet (GrIS) indicate that the climate of Greenland experienced multiple abrupt temperature increases during the last glacial period (LGP) known as Dansgaard-Oeschger (D-O) events (Dansgaard et al, 1993). D-Os have waiting times between consecutive events of around 1500 years and, with decreasing probability, 3000 and 4500 years (Alley et al, 2001) and are characterised by an initial abrupt warming of 10–16 ◦C (interstadial state) followed by a slow cooling which ends with an abrupt return to glacial background conditions (stadial state) (Johnsen et al, 1992; Kindler et al, 2014).

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