Earth System Physics and Climate Dynamics

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This research program seeks to understand phenomenology involving the coupled evolution of the solid Earth, the oceans, the atmosphere and continental ice sheets and sea ice. A unique contribution of this program involves the gravitationally self-consistent theory of Ice-Earth-Ocean interactions and relative sea level history. An important component of the proposed work will involve refinement of the ice sheet loading history of the continents during the most recent Late Quaternary ice-age cycle. The proposed work will also focus upon the explanation of why such glacial cycles are characterized by a distinctly "sawtooth" form in which the glaciation phase of the cycle is much slower and lasts longer than the deglaciation phase, a feature which appears to be controlled by extremely fast ice stream related instabilities that control the deglaciation phase. This aspect of the program has delivered the models of glaciation history that continue to be employed ubiquitously by the international community to provide the boundary conditions needed to support global climate model-based reconstructions of past climate conditions. Aside from continuing work on high resolution regional climate modeling of both modern and past climate states, a unique contribution of the Toronto group will continue to be work to more fully understand the so-called Dansgaard-Oeschger oscillation phenomenon that dominated climate variability during Marine Isotope Stage 3. As the Peltier group has shown these oscillations are triggered by the fast ice stream instabilities called Heinrich events for which a new theory has also been proposed that will be more fully explored in this proposed program of study. A primary focus of new research in this area will be on understanding the dependence of this D-O phenomenon upon the orbital insolation regime and other characteristics of the successful simulations that have already been produced. These D-O results have been shown to rely significantly upon the manner in which small scale ocean turbulence processes are parameterized in the global ocean component of the UofT climate model, especially the representation of ocean diapycnal diffusivity. A major contribution of the Toronto program continues to involve the development of theory and numerical simulation-based results that are leading to significant improvements in the representation of such small scale processes in low resolution ocean models. A particular focus in the next grant period will be upon the extent to which internal wave breaking may be contributing to ocean diapycnal diffusivity. This work is being supported by extremely high resolution MITgcm-based simulations with models explicitly forced by the astronomical tides and atmosphere derived surface forcing. This focus upon ocean turbulence processes based upon formal fluid mechanical analyses is the last of the linked set of investigations that will comprise the work to be undertaken in the next grant period.