Increased channelization of subglacial drainage during deglaciation of the Laurentide Ice Sheet

Abstract

The confi guration of subglacial meltwater is a critical control on ice sheet dynamics, and the presence of pressurized water distributed across the bed can induce dynamic instabilities. However, this process can be offset by effi cient evacuation of water within large subglacial channels, and drainage systems beneath alpine glaciers have been shown to become increasingly channelized throughout the melt season in response to the increased production of meltwater. This seasonal evolution has recently been inferred beneath outlet glaciers of the Greenland Ice Sheet, but the extent to which this process occurs across much larger spatial and temporal scales is largely unknown, introducing considerable uncertainty about the evolution of subglacial drainage networks at the ice sheet scale and associated ice sheet dynamics. This paper uses an unprecedented data set of over 20,000 eskers to reconstruct the evolution of channelized meltwater systems during the fi nal deglaciation of the Laurentide Ice Sheet (13-7 kyr B.P.). We demonstrate that eskers become more frequent during deglaciation and that this coincides with periods of increased rates of ice margin recession and climatic warming. Such behavior is reminiscent of the seasonal evolution of drainage systems observed in smaller glaciers and implies that channelized drainage became increasingly important during deglaciation. An important corollary is that the area of the bed subjected to a less effi cient pressurized drainage system decreased, which may have precluded dynamic instabilities, such as surging or ice streaming.