IUGG Gold Medal Lecture

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W. Richard Peltier, Department of Physics, University of Toronto

Wednesday July 17, 14:00-15:00

Session U03: Mathematics of Planet Earth: The Science of Data

Chair: Michael Sideris, IUGG President


Approximately 25 years ago an extra-ordinary discovery was made by Willi Dansgaard of the Niels-Bohr Institute at the University of Copenhagen and Hans Oeschger of the University of Bern. Based upon the analysis of oxygen isotopic data from the GRIP deep ice core that had been drilled to depth at Summit Greenland, it was demonstrated that North Atlantic climate variability during Marine Isotopic Stage 3 (MIS 3) was characterized by intense millennial timescale oscillations. These oscillations were later shown to follow the occurrence of Heinrich event instabilities of the eastern flank of the Laurentide ice sheet that had covered all of the northern part of the North American continent under Late Quaternary glacial conditions. Only recently has it proven possible to fully explain the millennial timescale D-O oscillation in which individual pulses of the variability have "relaxation oscillation form involving very fast timescale transitions from cold "stadial" conditions to warm "interstadial" conditions followed by a slow timescale return to the cold stadial state. In Peltier and Vettoretti (2014, GRL) it was demonstrated that this millennial timescale mode of climate variability that existed only under cold glacial conditions could be recovered in a modern coupled atmosphere-ocean-sea ice model run at high CMIP5 resolution. There it was shown that the D-O phenomenon appeared naturally as a nonlinear resonance of the climate system following a sharp Heinrich event-like diminution of the strength of the Atlantic Meridional Overturning Circulation (MOC). I will demonstrate that the success of this simulation of the millennial mode of glacial climate variability relies strongly upon the availability of accurate glacial boundary conditions determined on the basis of detailed analysis of the glacial isostatic adjustment (GIA) process. Subject to these boundary conditions the coupled sea ice-ocean-atmosphere system responds in the manner I have described as involving the action of a "kicked" salt oscillator in the North Atlantic Ocean, one that does not rely upon the exchange of fresh water between grounded ice sheets on the continents and the oceans as has often been suggested to be at the heart of the D-O mechanism.

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