Evidence of the Growth and Decay of Ice Sheets on Glaciated Landscapes

Abstract

The growth and decay cycle of ice sheets is forced by orbital variations of Earth around the Sun. Changes in solar inputs resulting from these variations are too small, however, to solely account for the expansion and retraction of huge ice masses. Instead, orbital climate forcing is supplemented by a series of positive feedback processes, which act to enhance climate cooling, resulting in large-scale glaciation. During deglaciation, as climate warms and ice sheets melt, feedback processes can act to speed up the decay of ice, which has been shown to result in short-term oscillations in climate conditions and, thus, ice sheet mass balance. Ice sheets grow first on land, as a response to climate cooling and the consequent lowering of equilibrium line altitudes. Such growth leads to changes in surface albedo (i.e., reflectivity of a surface, defined as the proportion of radiation reflected divided by the proportion of incoming radiation; hence, an albedo of 1 defines a surface with 100% reflectivity), atmospheric circulation, oceanic circulation and global sea level. Subsequently, shallow marine sections of continents may become glaciated when sea levels are close to their minimum. Ice sheet decay occurs first in lower latitudes and marine-based sections of ice sheets, leading to further sea-level rise. As deglaciation occurs, feedback may affect ice sheet breakup, resulting in accelerated decay and rapid short-term oscillations in ice sheet size.