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The increasing availability of LiDAR digital elevation models (DEMs) for Canada and the United States is improving our ability to recognize and detail the geomorphological record of former glacial lakes revealed by strandlines. More accurate strandline maps refine our understanding of glacial-isostatic adjustment (GIA), reveal information about deglacial ice margins, help identify rapid drawdown events and catastrophic flooding by ice dam failure, and advance models that connect waterplane curvature to age. Here we present new strandline maps in the Lake Superior Basin based on LiDAR DEMs from Wisconsin, Michigan, and Ontario. When combined with published records from Minnesota, they comprise the most extensive set of strandlines detailing former lake levels from any lake basin. Multiple lakes and lake phases are associated with these strandlines, including glacial lakes Wrenshall, Ontonagon, Duluth, Algonquin and Minong, as well as Holocene Lake Nipissing. The relative degree of strandline development varies widely, likely due to factors such as the availability of gravel and sand, length of time of formation, fetch, and local shoreline geometry (e.g. bay or headland). Strandlines for at least one level of glacial Lake Duluth are much more extensive on the southern shore, suggesting formation from only a very few numbers of storms with winds from the north. New LiDAR DEMs from the Sault Ste. Marie region are particularly helpful because they allow us to determine isobases (lines of equal GIA) across the primary basin outlet with high confidence. In general, our work supports the work of prior researchers, but adds details that are easily missed by field surveys or when using coarser resolution DEMs. 

Large proglacial lakes could have been a significant methane source during the last deglaciation. Today, proglacial lakes are small and mostly limited in the northern hemisphere to the margins of ice sheets in Greenland, Alaska, and Canada, but much larger proglacial lakes collectively flooded millions of square kilometers in the northern hemisphere over the last deglacial period. We synthesize new and existing methane flux measurements from modern proglacial lakes in Alaska and Greenland and use these data together with reconstructed lake area and bathymetry, new paleorecords of sediment organic geochemistry, carbon accumulation, and other proxies to broadly constrain the possible deglacial methane dynamics of a single large North American proglacial lake, Lake Agassiz. While large influxes of glaciogenic material contributed to rapid organic carbon burial during initial lakes phases, limited bioavailability of this carbon is suggested by its likely subglacial origin and prior microbial processing. Water depths of >20 m across 37–90% of the lake area facilitating significant oxidation of methane within the water column further limited emissions. Later phases of lake lowering and subsequent re-expansion into shallow aquatic and subaerial environments provided the most significant opportunity for methane production according to our estimates. We found that Lake Agassiz was likely a small source [0.4–2.7 Tg yr−1 mean (0.1–9.9 Tg yr−1 95% CI)] of methane during the last deglaciation on par with emissions from modern wildfires. Although poor constraints of past global proglacial lake areas and morphologies currently prevent extrapolation of our results, we suggest that these systems were likely an additional source of methane during the last deglacial transition that require further study.