On the Spreading of Glacial Meltwater in the Western North Atlantic. Part II: Interactions with the Gulf Stream

Abstract The dispersal of meltwater discharged from the Laurentian Channel (LC) is investigated from numerical experiments with an eddy-resolving model representing the western North Atlantic during the last ice age. Meltwater dispersal is simulated over a full summer, when glacial ablation rates were presumably the highest. In our experiments, meltwater forms a buoyant plume, which flows to the southwest along the continental slope owing to the Coriolis force. Four mechanisms of offshore export are identified. 1) Meltwater is carried seaward by Ekman currents driven by upwelling-favorable winds along the slope. 2) Part of it is entrained away from the slope by meander crests and warm-core rings of the Gulf Stream (GS) between the LC and Cape Hatteras. 3) The other part is generally diverted offshore by the GS near Cape Hatteras, where the GS leaves the slope. 4) Meltwater can be trapped in a GS meander trough that pinches off and produces a cold-core ring, leading to its penetration into the subtropical gyre. In turn, the buoyant plume has relatively small but noticeable effects on the GS. In the western, weakly meandering segment of the GS, the vertical shear in horizontal velocity is generally reduced due to the presence of melt (light) water along the inshore flank of the GS. Our results are discussed in light of (i) a two-layer theory of a surface density front subjected to background flow and wind stress and (ii) sediment records from the Laurentian Fan and the Sargasso Sea.