Campuses:

A Sea Ice Switch Mechanism for the Glacial Cycles

Thursday, September 27, 2001 - 9:30am - 10:30am
Keller 3-180
Eli Tziperman (Weizmann Institute of Science)
A novel mechanism and model for the glacial-interglacial oscillations will be described. The dominant 100 kyr oscillation in the model land ice volume has the familiar saw-tooth shape of climate proxy records. The glacial oscillation in the proposed mechanism is a nonlinear relaxation oscillation. The transition from the slow to fast phases of the oscillation results from the behavior of sea ice which controls, via its albedo and insulating effects, the atmospheric poleward moisture fluxes and therefore the precipitation that enable the land ice-sheet growth. This control, and the rapid growth and melting of the sea ice, allow the sea ice to rapidly switch the climate system from a slow growing ice-sheet phase to a fast retreating ice-sheet phase, and to shape the oscillation's saw-tooth structure. Milankovitch insolation changes due to variations in the earth orbit around the sun act as a pacemaker, setting the phase of the oscillation via nonlinear phase locking by directly controlling summer melting of ice sheets.

The proposed sea ice switch mechanism for the glacial cycles also results in a natural explanation for the transition from 41 kyr glacial cycles to 100 kyr cycles about one million years ago. The transition according to this explanation is due to a bifurcation of the climate system that resulted in the activation of the sea ice switch at that time.