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

古气候研究表明，地球气候经历了突然的气候变化，涉及大气和海洋在十年到千年的时间尺度上的重要重组。最引人注目的机制，以解释这些重组在第四纪晚期有关的影响，淡水排放的大西洋经向翻转环流，这在重新分配大量的热量在北方半球发挥了重要作用。末次冰期末和当前间冰期（全新世）的气候变化大部分是由于大陆冰盖的衰减，这导致了大量冰川融水的释放，这些融水积累在大型冰坝湖泊中。冰与海洋相互作用的最好例子之一发生在大约8200年前，当时哈德逊湾上的冰突然腐烂，使冰川湖阿加西斯湖和奥吉布韦湖突然流入北大西洋，导致全球范围的冷却。然而，这种淡水扰动的精确影响受到海洋沉积物记录的质疑，这些记录表明，包括所谓的8.2 ka冷却事件的时间间隔的特点是多次爆发的融水。然而，支持阿加西-奥吉布韦湖多步最终排水的地质数据有限。本研究项目的重点是奥吉布韦湖的后期历史，通过研究新认识的海岸线，反映了奥吉布韦湖水位的突然下降，并通过记录沉积序列，可能记录排水事件（S）之前，在东北部安大略和西北部魁北克的最终湖泊排水。拟议的研究项目将导致几个研究生的高级培训，这将有助于研究融水量估计和融水突然排放的年表。这项研究计划的长期目标是增加我们对淡水排放在气候突变中的作用的理解，并为预测气候模型提供边界条件。考虑到与冰冻圈对当前全球变暖的反应有关的不确定性，这是一个重要的贡献。

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.