Jacky Austermann and Ben Stoker, both at Columbia University, Palisades, USA, will present

Proglacial Lakes as Windows into GIA and Drivers of Ice-Sheet and Climate Chang

Part I (Jacky):
Proglacial lakes are lakes that form around the margins of ice sheets. Both talks will focus on proglacial lakes around the Laurentide Ice Sheet. In the first part, we will present simulations of the Last Glacial Cycle where we included self-consistently evolving proglacial lakes in a glacial isostatic adjustment (GIA) model. We found that proglacial lakes are up to five times bigger (by volume) during the deglaciation compared to glaciation for the same ice position and size, which is a result of the differences in the position and size of the peripheral bulge. Proglacial lake depth affects ice dynamics at the grounding line and we show that indeed at certain times during the deglaciation, Laurentide ice-margin retreat rate is positively correlated with proglacial lake presence. This supports an early hypothesis that GIA – by shaping proglacial lakes – plays an active role in accelerating collapse of the deglacial Laurentide Ice Sheet.

Part II (Ben):
The new NADI-1 reconstruction of the Laurentide Ice Sheet margin chronology allows us to update the GIA-proglacial lakes model to reconstruct proglacial lake evolution more accurately. Despite widespread evidence of glacial lake extent and dynamics at the basin-scale, continental-scale compilations of this evidence is outdated and does not take advantage of the advances in surficial mapping. Here we will present a new effort to compile paleo lake shorelines across North America. We find that our lake compilation enhances existing databases by orders of magnitude along the western margin and therefore increases important constraints on GIA in the continental interior. We have compared our lake database to an ensemble of the GIA-proglacial lakes models and will show the new constraints that this data-model comparison puts on both ice reconstruction and solid Earth properties. Further, we have used our best-fitting simulations to calculate freshwater routing over the deglaciation, providing new, data calibrated model predictions on where and how much freshwater forcing might have affected ocean circulation.