Coupled energy‐balance/ice‐sheet model simulations of the glacial cycle: A possible connection between terminations and terrigenous dust

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Abstract
We apply a coupled energy‐balance/ice‐sheet climate model in an investigation of northern hemisphere ice‐sheet advance and retreat over the last glacial cycle. When driven only by orbital insolation variations, the model predicts ice‐sheet advances over the continents of North America and Eurasia that are in good agreement with geological reconstructions in terms of the timescale of advance and the spatial positioning of the main ice masses. The orbital forcing alone, however, is unable to induce the observed rapid ice‐sheet retreat, and we conclude that additional climatic feedbacks not explicitly included in the basic model must be acting. In the analyses presented here we have parameterized a number of potentially important effects in order to test their relative influence on the process of glacial termination. These include marine instability, thermohaline circulation effects, carbon dioxide variations, and snow albedo changes caused by dust loading during periods of high atmospheric aerosol concentration. For the purpose of these analyses the temporal changes in the latter two variables were inferred from ice core records. Of these various influences, our analyses suggest that the albedo variations in the ice‐sheet ablation zone caused by dust loading may represent an extremely important ablation mechanism. Using our parameterization of “dirty” snow in the ablation zone we find glacial retreat to be strongly accelerated, such that complete collapse of the otherwise stable Laurentide ice sheet ensues. The last glacial maximum configurations of the Laurentide and Fennoscandian complexes are also brought into much closer accord with the ICE‐3G reconstruction of Tushingham and Peltier (1991,1992) and the ICE‐4G reconstruction of Peltier (1994) when this effect is reasonably introduced.