The West Antarctic Ice Sheet: Instability, disintegration, and initiation of Ice Ages

An ice age model is proposed in which glacial‐interglacial global climatic cycles are controlled by interactions between the cryosphere, hydrosphere, and atmosphere in the Atlantic environment. In the model, climatic change results from instabilities which develop in the snowfields or ice sheets of North America, Europe, and Antarctica. Disintegration of the West Antarctic ice sheet (that portion of the Antarctic ice sheet lying in the western hemisphere) initiates a chain of events which culminates in a global ice age. Ten independent bodies of data can be interpreted as evidence that the West Antarctic ice sheet has been and is disintegrating. The dynamics of the Ross Sea ice drainage system of Antarctica is examined to determine what controls disintegration and recovery of the West Antarctic ice sheet. It is concluded that disintegration is controlled by ice streams which drain the inherently unstable West Antarctic ice sheet and recovery is controlled by outlet glaciers which drain the inherently stable East Antarctic ice sheet. Glacial stability in both cases is determined by the degree of coupling between the ice sheet and its bed. Ice drainage channels develop when this coupling is weakened normal to the margin of an ice sheet and can lead to surges in ice streams or outlet glaciers. Ice shelves develop when this coupling is weakened parallel to the margin of an ice sheet and can lead to a rapid grounding line retreat of floating ice tongues or ice shelves. An inflection maximum on the ice sheet surface migrates inland during a surge and migrates seaward after the surge is spent. A transition zone between the ice sheet and the ice shelf widens during a grounding line retreat inland and narrows during a grounding line advance seaward. Inflection line and grounding line migrations combine to give the ice sheet a concave surface during retreat and a convex surface during advance. A train of surging segments in an ice stream lowers the ice sheet in stages, creating a terraced ice stream surface which causes rapid discontinuous retreats of the grounding line. Rapid glacial recovery following a surge can truncate the advancing ice sheet‐ice shelf boundary. Today at least one West Antarctic ice stream is terraced and at least one East Antarctic outlet glacier is truncated in the Ross Sea ice drainage system. If this condition is general, the West Antarctic ice sheet is disintegrating along the Siple Coast as a result of surging ice streams and is recovering along the Transantarctic Mountains as a result of thickening outlet glaciers. The competition between these processes will provide a critical test of the ice age model, which predicts that progressive disintegration of the West Antarctic ice sheet results in progressive growth of adjacent parts of the East Antarctic ice sheet.