Dick Peltier - University of Toronto - EAPS Department Lecture Series

During the period from 60,000 to 35,000 years ago, Summit-Greenland ice-core records of the oxygen isotopic ratio exhibit intense millennium timescale oscillations. These Dansgaard-Oeschger oscillations have been interpreted to represent the variations in North Atlantic air temperature caused by correlative changes in the strength of North Atlantic Deep Water (NADW) formation in the adjacent Greenland-Iceland-Norwegian (GIN) and Labrador Seas. Although several mechanisms have been suggested as ultimate cause of the varying strength of deep water production on the millennium timescale, no convincing evidence has been provided in favor of any of these. I'll describe the application of a recently constructed comprehensive model of glacial climate to establish the ability of such a model to fully embody the D-O oscillation phenomenon. This is shown to involve a "salt oscillation" of relaxation oscillator form that is governed by an interplay between convective destabilization of the water column in the North Atlantic, sea ice cover expansion and contraction, and the linked and oscillatory variability of salinity between the subtropical gyre and the sea ice covered portion of the North Atlantic Basin. Correlative north-south oscillations in the position of the ITCZ are also intimately involved. This oscillator is shown to be kicked into action by the forcing provided by individual Heinrich events which immediately precede such D-O behavior.