Coupled Northern Hemisphere permafrost–ice-sheet evolution over the last glacial cycle

M Willeit,A Ganopolski

doi:10.5194/cp-11-1165-2015

Abstract

Abstract. Permafrost influences a number of processes which are relevant for local and global climate. For example, it is well known that permafrost plays an important role in global carbon and methane cycles. Less is known about the interaction between permafrost and ice sheets. In this study a permafrost module is included in the Earth system model CLIMBER-2, and the coupled Northern Hemisphere (NH) permafrost–ice-sheet evolution over the last glacial cycle is explored. The model performs generally well at reproducing present-day permafrost extent and thickness. Modeled permafrost thickness is sensitive to the values of ground porosity, thermal conductivity and geothermal heat flux. Permafrost extent at the Last Glacial Maximum (LGM) agrees well with reconstructions and previous modeling estimates. Present-day permafrost thickness is far from equilibrium over deep permafrost regions. Over central Siberia and the Arctic Archipelago permafrost is presently up to 200–500 m thicker than it would be at equilibrium. In these areas, present-day permafrost depth strongly depends on the past climate history and simulations indicate that deep permafrost has a memory of surface temperature variations going back to at least 800 ka. Over the last glacial cycle permafrost has a relatively modest impact on simulated NH ice sheet volume except at LGM, when including permafrost increases ice volume by about 15 m sea level equivalent in our model. This is explained by a delayed melting of the ice base from below by the geothermal heat flux when the ice sheet sits on a porous sediment layer and permafrost has to be melted first. Permafrost affects ice sheet dynamics only when ice extends over areas covered by thick sediments, which is the case at LGM.

Highlights

The existence and thickness of permafrost is a result of the history of energy balance at the Earth’s surface and the deep Earth heat flow
A newly developed permafrost module has been integrated into the CLIMBER-2 Earth system model of intermediate complexity (Brovkin et al, 2002; Ganopolski et al, 2001; Petoukhov et al, 2000)
The model is generally able to reproduce the main patterns in mean annual ground surface temperature (MAGST) except for southern Siberia, where the model underestimates the ground temperature by up to 5 ◦C

Summary

Introduction

The existence and thickness of permafrost is a result of the history of energy balance at the Earth’s surface and the deep Earth heat flow. Assuming that the geothermal heat flow did not notably change over the Quaternary, the present permafrost state has been shaped mainly by past surface ground temperature variations (Osterkamp and Gosink, 1991). Previously glaciated regions will show a lesser volume of frozen ground than unglaciated regions with similar climatic histories. In this regard it is important that Canada was heavily glaciated while most of Siberia had remained ice-free during the past glacial cycle. The present permafrost thickness in Siberia is much greater than in Canada, even though the climates are similar

Methods

Results

Conclusion