Modeling Northern Hemisphere ice-sheet distribution during MIS 5 and MIS 7 glacial inceptions

F Colleoni,S Masina,C Ritz,A Navarra,V Peyaud,B Otto-Bliesner,A Cherchi

doi:10.5194/cp-10-269-2014

Abstract

Abstract. The present manuscript compares Marine Isotope Stage 5 (MIS 5, 125–115 kyr BP) and MIS 7 (236–229 kyr BP) with the aim to investigate the origin of the difference in ice-sheet growth over the Northern Hemisphere high latitudes between these last two inceptions. Our approach combines a low resolution coupled atmosphere–ocean–sea-ice general circulation model and a 3-D thermo-mechanical ice-sheet model to simulate the state of the ice sheets associated with the inception climate states of MIS 5 and MIS 7. Our results show that external forcing (orbitals and GHG) and sea-ice albedo feedbacks are the main factors responsible for the difference in the land-ice initial state between MIS 5 and MIS 7 and that our cold climate model bias impacts more during a cold inception, such as MIS 7, than during a warm inception, such as MIS 5. In addition, if proper ice-elevation and albedo feedbacks are not taken into consideration, the evolution towards glacial inception is hardly simulated, especially for MIS 7. Finally, results highlight that while simulated ice volumes for MIS 5 glacial inception almost fit with paleo-reconstructions, the lack of precipitation over high latitudes, identified as a bias of our climate model, does not allow for a proper simulation of MIS 7 glacial inception.

Highlights

Glacial inceptions represent a transition from a warm to a cold mean climate state (Calov et al, 2005b)
Dutton et al (2009) suggest that during the penultimate interglacial, ≈ 245 kyr BP, sea level never rose above present-day mean sea level. Because of those greenhouse gases (GHGs) particularities and of the difference in sea level between MIS 5 and MIS 7, we focus our investigations on the Northern Hemisphere ice-sheet distribution of MIS 5 (≈ 125–116 kyr BP) and MIS 7 (≈ 236–229 kyr BP) glacial inceptions
To retrieve a time evolution temperature index given by the combination of insolation, GHGs and sea-ice albedo, we considered the reconstructions by Köhler et al (2010) who used an idealized radiative model applied to various proxy records from Antarctica

Summary

Introduction

Glacial inceptions represent a transition from a warm to a cold mean climate state (Calov et al, 2005b). Considering the sea-level records during these warm-to-cold transitions, Northern Hemisphere ice sheets were only little developed over North America and Eurasia compared to the glacial maxima (Fig. 1d). It is accepted that Northern Hemisphere ice sheets started to develop only if both insolation and greenhouse gases (GHGs) dropped significantly (e.g., Berger, 1978; Bonelli et al, 2009). Similarities with GHGs trends are observed in the East Antarctica mean annual temperature anomaly record (Fig. 1g, Jouzel et al, 2007). The largest drop in Northern Hemisphere high latitudes summer insolation is observed after the last interglacial, ≈ 125 kyr BP (Fig. 1b)

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Discussion

Conclusion