Terminating the Last Interglacial: The Role of Ice Sheet-Climate Feedbacks in a GCM Asynchronously Coupled to an Ice Sheet Model

Climatic deterioration in northeastern Canada following the last interglacial resulted in the formation and abrupt expansion of the Laurentide Ice Sheet. However, the physical mechanisms leading to rapid ice sheet expansion are not well understood. Here, the authors report on experiments using an ice sheet model asynchronously coupled to a GCM to investigate the role of ice sheet climate feedbacks in terminating the last interglacial period. In agreement with simpler models, the experiments indicate that a specific type of ice albedo feedback, the small ice cap instability, is the dominant process controlling rapid expansion of the Laurentide Ice Sheet. As ice elevations increase in northeastern Canada, a stationary wave forms and strengthens over the Laurentide Ice Sheet, which acts to hinder further expansion of the ice margin and reduce the effect of the small ice cap instability. The sensitivity of these feedbacks to ice topography results in a reduction in simulated ice volume when the communication interval between the GCM and ice sheet model is lengthened since this permits larger gains in ice elevation between GCM updates and biases the simulation toward a stronger stationary wave feedback. The shortest communication interval (500 yr) leads to a Laurentide ice volume of 6 x 10(6) km(3) in 10 kyr, which is less than ice volume estimates based on the geological record but is a substantial improvement over previous GCM studies. The authors discuss potential improvements to the asynchronous coupling scheme that would more accurately resolve ice sheet climate feedbacks, potentially leading to greater simulated ice volume.