Heinrich event 1: an example of dynamical ice-sheet reaction to oceanic changes

J Álvarez-Solas,T Dokken,A Ganopolski,S Charbit,C Dumas,C Ritz,M Montoya,G Ramstein,K Nisancioglu

doi:10.5194/cp-7-1297-2011

Abstract

Abstract. Heinrich events, identified as enhanced ice-rafted detritus (IRD) in North Atlantic deep sea sediments (Heinrich, 1988; Hemming, 2004) have classically been attributed to Laurentide ice-sheet (LIS) instabilities (MacAyeal, 1993; Calov et al., 2002; Hulbe et al., 2004) and assumed to lead to important disruptions of the Atlantic meridional overturning circulation (AMOC) and North Atlantic deep water (NADW) formation. However, recent paleoclimate data have revealed that most of these events probably occurred after the AMOC had already slowed down or/and NADW largely collapsed, within about a thousand years (Hall et al., 2006; Hemming, 2004; Jonkers et al., 2010; Roche et al., 2004), implying that the initial AMOC reduction could not have been caused by the Heinrich events themselves. Here we propose an alternative driving mechanism, specifically for Heinrich event 1 (H1; 18 to 15 ka BP), by which North Atlantic ocean circulation changes are found to have strong impacts on LIS dynamics. By combining simulations with a coupled climate model and a three-dimensional ice sheet model, our study illustrates how reduced NADW and AMOC weakening lead to a subsurface warming in the Nordic and Labrador Seas resulting in rapid melting of the Hudson Strait and Labrador ice shelves. Lack of buttressing by the ice shelves implies a substantial ice-stream acceleration, enhanced ice-discharge and sea level rise, with peak values 500–1500 yr after the initial AMOC reduction. Our scenario modifies the previous paradigm of H1 by solving the paradox of its occurrence during a cold surface period, and highlights the importance of taking into account the effects of oceanic circulation on ice-sheets dynamics in order to elucidate the triggering mechanism of Heinrich events.

Highlights

A major effort has been devoted in the last decade in order to understand rapid glacial climate variability as registered in many climatic archives
Heinrich event 1 (H1) and earlier H events show the largest ice rafted debris (IRD) peaks occurring several hundred years after the onset of the cold period (Hemming, 2004; Jonkers et al, 2010; Roche et al, 2004), suggesting that the initial Atlantic meridional overturning circulation (AMOC) reduction could not have been caused by the Heinrich events themselves
The focus here is on H1, the initial requirement is potentially valid for all six Heinrich Events, given the fact that they all occur during a cold stadial period

Summary

Introduction

A major effort has been devoted in the last decade in order to understand rapid glacial climate variability as registered in many climatic archives. Greenland ice core records indicate that the last glacial period was punctuated by more than 20 abrupt warmings larger than 10 K (Dansgaard-Oeschger events) followed by progressive cooling (Dansgaard et al, 1993; Grootes et al, 1993). As revealed by the study of marine sediment cores in the North Atlantic, six of the temperature minima in Greenland were coeval with unusual amounts of ice rafted debris (IRD) originating primarily from the areas around Hudson Bay (Bond et al, 1992). Several mechanisms have been proposed to explain these anomalous ice discharge events, known as Heinrich events. The first considers these to be internal oscillations of the Laurentide ice sheet (LIS) associated with alterations of basal conditions (MacAyeal, 1993; Calov et al, 2002). A sudden break-up of ice shelves has been implicated via atmospheric warming (Hulbe et al, 2004) or tidal effects (Arbic et al, 2004)

Results

Discussion

Conclusion