On the factors behind large Labrador Sea tides during the last glacial cycle and the potential implications for Heinrich events

Abstract

Labrador Sea (LS) tidal elevations over the last glacial cycle are investigated in a near-global numerical model that accurately captures the present-day tides. From 65 ka to 7 ka, the modeled elevations at the debouchement point of the Hudson Strait ice stream in the LS are exceptionally large, comparable to the largest elevations seen anywhere in the present-day ocean. New numerical simulations performed for this article demonstrate that both local changes in basin geometry (e.g., ice cover over Hudson Bay) and changes outside of the LS led to enhanced LS paleotides. New simulations run at higher horizontal resolution and a considered examination of uncertainties, including uncertainties in the adopted sea level models, strengthen confidence in the robustness of the large LS paleotides. The tide model is run with both spatially uniform sea level drops (taken from curves of eustatic and Red Sea sea levels versus time) and spatially variable sea level maps (taken from two different gravitationally self-consistent viscoelastic solid earth/sea level models, which both account for ice sheet geometry). The tides are larger when the spatially variable sea level models are used. Observations in present-day Antarctica indicate that the mechanical action of tides significantly impacts the dynamics of both continental ice streams and their associated floating ice shelves. It is postulated here that large LS paleotides played a key role in the formation of Heinrich event icebergs, that is, massive discharges of ice from the LS into the glacial North Atlantic ocean. The paleotide calculations described here provide a potential explanation for why the LS region, more than any other, dominated the production of Heinrich event icebergs. Most previous hypotheses of a tidal role in climate variability and ice sheet dynamics focus on tidal mixing. In contrast, here the role of tidal mechanical forcing of ice sheets is emphasized.