On the Entrainment of Glacial Meltwater by the Gulf Stream

The fate of glacial meltwater introduced into the ocean is an important problem both in paleoceanography and in modern oceanography. A long-standing question in paleoceanography concerns the evolution and consequences of the glacial meltwater delivered from the great ice sheets which covered a large fraction of North America and Europe during glacial periods. Although the associated rise in mean sea level of about 130 m has long been estimated, the pathways and impacts of the glacial meltwater for ocean circulation and climate remain poorly understood. Notably, the ocean components of climate models do not generally have a spatial resolution that is fine enough to properly simulate coastal phenomena which are known to contribute to the offshore export of shelf water in the modern ocean.

Here we apply a regional eddy-revolving numerical model of ocean circulation in order to explore the pathways of glacial meltwater emanating from the St. Lawrence Channel – a major ice stream of the Laurentide Ice Sheet of North America during the last glacial period. Emphasis is placed on the offshore entrainment of glacial water by the Gulf Stream (GS), which according to paleoceanographic observations detached from the continental slope near Cape Hatteras, as it does today. First, a simulation of the eddying circulation in the glacial western North Atlantic is obtained by integrating the regional model to statistical steady state under glacial atmospheric forcing. Second, a series of glacial water discharge experiments are conducted for various assumptions about the discharge, including its volume transport, its density, and its seasonal timing. Mechanisms of glacial water export away from the slope are identified, such as the eastward entrainment by (anticyclonic) warm core rings and the subsequent incorporation of the glacial water into the GS offshore. The implications of our results for the interpretation of sediment records from the Laurentian Fan and for the simulation of glacial water discharges in paleoclimate models are then clarified.