Growth and decay cycles of Quaternary ice sheets

Abstract

The growth and decay cycle of ice sheets is paced by orbital variations of the Earth around the Sun. Change in solar inputs resulting from these variations in the Northern Hemisphere trigger the expansion and retraction of huge ice masses, and are globalized and amplified through a series of positive feedback processes. For example, during periods of cooling, the oceans become more productive and draw carbon dioxide from the atmosphere leading to further cooling. During deglaciation, as climate warms and ice sheets melt, the reverse feedback occurs leading to enhanced warming. As ice sheets decay, meltwater is issued into the ocean and can interfere with thermo-haline processes, resulting 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 consequent lowering of equilibrium line altitudes. Such growth leads to changes in the surface albedo, ocean conditions, atmospheric 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 sea-level rise. As deglaciation continues, feedbacks may force accelerated decay of ice and lead to rapid short-term oscillations in climate conditions (including reversals) and ice-sheet mass balance and dynamics. Hence, warming during deglaciation is characterized by large (±2–5°C) short-term (decadal) changes to regional climate conditions, especially in maritime locations such as southern Greenland.