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，包括在十年到千年的时间尺度上对大气和海洋进行了重要的重组。解释第四纪晚期这些重组的最令人信服的机制与淡水排放对大西洋子午线翻转环流的影响有关，大西洋子午线翻转环流在北半球重新分配大量热量方面发挥着基础性作用。上一次冰期末期和当前间冰期(全新世)的气候变化在很大程度上是由于大陆冰盖的退化，导致大量冰川融水释放，积聚在大型冰坝湖泊中。冰海相互作用的最好例子之一发生在大约8200年前，当时哈德逊湾上空不断腐烂的冰突然允许冰川湖阿加西和奥吉布韦突然流入北大西洋，导致全球范围的降温。然而，这种淡水扰动的确切影响受到海洋沉积物记录的质疑，这些记录表明，构成所谓8.2-ka冷却事件的时间间隔的特征是多次爆发融化水。然而，支持阿加西-奥吉布维湖多步骤最终排水的地质数据有限。本研究计划通过研究新发现的反映奥吉布维湖水位突然下降的海岸线(S)，以及记录可能记录安大略省东北部和魁北克省西北部最终湖泊排水之前的排水事件的沉积序列，重点关注奥吉布维湖的晚期历史。拟议的研究项目将导致对几名研究生进行高级培训，这将有助于研究融水水量估计和融水突然排放的年表。这项研究计划的一个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，这是一项重要贡献。

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.