The glacial lakes of northern Quebec-Labrador and their contribution to the meltwater discharges of the late deglaciation and early Holocene climate interval

过去15000年至7000年的气候变化通常与大型冰川湖的排水有关，这些冰川湖是在最后一个冰河时代的腐烂冰块边缘形成的。据信，这些大规模的融水爆发扰乱了北大西洋环流，而北大西洋环流在调节地球气候方面起着重要作用。这些以前的气候强迫事件现在受到关注，因为越来越多的研究表明，目前格陵兰岛和其他北极冰川融化所释放的淡水增加，可能会导致海洋温盐环流减缓，并引起重要的气候反馈。

The climate variability of the last 15,000 to 7,000 years is commonly linked to the drainage of large glacial lakes that had developed at the margins of the decaying ice masses of the last Ice Age. These massive outbursts of meltwater are believed to have disturbed the North Atlantic Ocean circulation, which plays a fundamental role in regulating Earth's climate. These former climate-forcing events are now under focus due to a growing number of studies showing that the present-day increase in freshwater releases from the melting of Greenland and other Arctic glaciers may potentially lead to a slowdown of the ocean thermohaline circulation and cause important climate feedbacks. In northern Quebec and Labrador, the last deglaciation led to the formation of several large glacial lakes that invaded the main river valleys around Ungava Bay. These ice-dammed lakes drained into the Labrador Sea where the repeated and sustained meltwater discharges likely destabilized the ocean surface conditions and altered/suppressed deepwater formation taking place in this key sector of the ocean. Although the drainage of these glacial lakes may form an outstanding analogue for modern processes, assessing the precise impact of these meltwater discharges on the ocean system and climate is prevented by uncertainties on the pattern of ice retreat and the lack of constraints on the configuration (meltwater volumes) of these lakes. Furthermore, the timing of the main stages of the deglaciation remains poorly constrained. This research program is based on the integration of field-based investigations and novel analytical methods to the study of the sediment and geomorphic records of north-central Ungava and Labrador. The main objectives are to: (1) characterize the dynamics and evolution of the ice margin during the deglaciation through systematic mapping and geochemical analyses of glacial sediments and landforms; (2) reconstruct the extent and depth of 8 glacial lakes though mapping and elevation measurements of raised shorelines; and (3) provide realistic estimates for the lake meltwater volumes using GIS models. Cosmogenic nuclide dating of shorelines and outburst flood deposits will further constrain the chronology of the lake development and drainage, which should contribute to place these meltwater discharges within the North Atlantic deglaciation framework. Altogether, this research program will improve the accuracy of paleogeographic reconstructions by providing a comprehensive knowledge of ice-flow patterns and ice sheet dynamics, which are critical elements in both fundamental and applied sciences. These results will also improve our understanding of the role of meltwater discharges in past climate perturbations and refine boundary conditions that are critically required by paleo/predictive climate models to fully assess the impact of freshwater inputs on ocean circulation and climate.