Sea-Level Control of Ice Sheet Disintegration

Abstract

A simplified model of the Laurentide (North American) Ice Sheet shows that an initial rise in sea level, produced by melting along its landward margin, would trigger an instability and, hence, a major retreat of its sea-level controlled marine margin. Recession of the seaward margin would contribute further to the rise in sea level, leading to retreat rates up to four times faster than on land, which is primarily controlled by ablation.

Of the major late Quaternary ice sheets, only those in the northern hemisphere had extensive terrestrial margins with ablation zones which would have been sensitive to changes in insolation. Marine ice-sheet margins, which predominated in the southern hemisphere and in the high latitudes of the northern hemisphere, are less sensitive to variations in ablation. Indeed, few have ablation zones, mass removal being primarily by iceberg calving. However, marine margins are extremely sensitive to changes in sea level and can only be stabilized if they are buttressed by floating ice shelves pinned to the sea floor at islands and shoals.

Using as an input the retreat history of the terrestrial margin, as deduced from dated moraines, a sea-level curve representing the changing volume of the Laurentide Ice Sheet was produced. This duplicated the essential features of the CLIMAP sea-level curve based on oxygen-isotope ratios. Output from the ice-sheet model includes cross-sections showing the positions of the terrestrial and marine margin and the major ice domes as a function of time, as well as the extent of actively buttressing ice shelves and the velocity of the ice discharge across marine grounding lines.