The Contribution of Atmospheric Feedbacks on Ice Sheet Evolution during the Last Deglaciation

Abstract:

Our understanding of ice and climate changes over the last deglaciation has been partly distorted by our reliance on models of ice and climate that are one-way coupled, with either forced ice sheets or forced climate. This, along with a snapshot approach to paleo-climate modelling, leaves unclear how ice sheet-induced changes in atmospheric circulation feed back onto the ice sheets and the rest of the climate system.

The use of bi-directionally coupled ice-climate models for a period of this duration is still in its infancy and generally requires the use of highly simplified representations of climate at resolutions too low to accurately resolve large-scale atmospheric circulation. Also, these configurations complicate the isolation of feedbacks and are unlikely to produce an ice sheet history consistent with available paleo constraints. Therefore, as a first step towards a fully coupled transient analysis, we have undertaken an ensemble of transient simulations of the last deglaciation using the earth system model, Planet Simulator, with PMIP4 boundary conditions and the GLAC1-D global ice sheet chronology. We have also produced sensitivity ensembles that isolate the effects of orographic and diabatic forcings of land ice on climate. Notably, the employed atmospheric component is of adequate resolution (T42) to resolve the stationary planetary waves that control on average temperature and wind fields.

On the basis of this ensemble, we analyse the impact that evolving ice sheets have on atmospheric circulation patterns and the atmospheric fields that largely control terrestrial ice sheet evolution. Earlier analyses showed that the south-eastern margin of the Laurentide Ice Sheet controls the northward extent of the winter-time North Atlantic jet (Andres and Tarasov, Climate of the Past, 2019). Here, we focus on summer conditions, which play a more important role in ice sheet surface mass balance and evolution.