Evolution of glacial Lake Ojibway and impact of meltwater discharges on early Holocene abrupt climate changes

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Paleoclimate research has revealed that the Earth's climate experienced abrupt climate changes involving important reorganizations of the atmosphere and oceans at decadal to millennial timescales. The most compelling mechanism to explain these reorganizations during the Late Quaternary relate to the impact of freshwater discharges on the Atlantic Meridional Overturning Circulation, which plays a fundamental role in redistributing vast amounts of heat in the Northern Hemisphere. Much of the climate variability of the end of the last glacial period and current interglacial (the Holocene) was due to the decay of continental ice sheets, which gave rise to massive releases of glacial meltwaters that accumulated in large ice-dammed lakes. One of the best examples of ice-ocean interaction occurred about 8200 years ago when the decaying ice over Hudson Bay suddenly allowed glacial lakes Agassiz and Ojibway to drain abruptly into the North Atlantic and cause a global-scale cooling. The precise impact of this freshwater perturbation is however questioned by marine sediment records that indicate that the time interval comprising the so-called 8.2-ka cooling event was characterized by multiple outbursts of meltwaters. Yet geological data supporting a multi-step final drainage of Lake Agassiz-Ojibway is limited. This research program focuses on the late-stage history of Lake Ojibway though the study of newly recognized shorelines that reflect abrupt drawdown(s) of Ojibway lake levels and by documenting sedimentary sequences that possibly record drainage episode(s) preceding the final lake drainage in northeastern Ontario and northwestern Quebec. The proposed research projects will result in the advanced training of several graduate students, which will contribute to the research on meltwater volume estimates and on the chronology of the abrupt meltwater discharges. A long-term objective of this research program is to increase our understanding of the role of freshwater discharges in abrupt climate changes and provide boundary conditions to predictive climate models. This represents an important contribution considering the uncertainties related to the response of the cryosphere to the current global warming.