Abstract

During the last deglaciation (20,000 – 6,000 yrs BP), many prominent abrupt climate cooling episodes (e.g. 8.2-kyr-event, Younger Dryas, Heinrich Event 1) aligned with times of enormous meltwater and iceberg discharge to the North Atlantic. A freshening of the subpolar gyre is thought to have weakened the AMOC and initiated a cooling. But exactly how changes in high latitude runoff impacted the AMOC is unclear. The classic way to model these events has been to look at the response of the AMOC to an instantaneous freshening of the subpolar North Atlantic gyre (50-70N). In this talk I will show that during periods of massive glacial lake drainage, a large fraction of meltwater would have first been routed to the subtropics. The meltwater would have then been advected northwards to the subpolar gyre, but mixing with the ambient ocean along the way resulted in the meltwater becoming saltier and less effective at weakening NADW formation. The subtropical pathway simulated by the model is supported by evidence that massive (>300m thick) icebergs drifted along the east coast of North America to Southern Florida during the last deglaciation. Once the meltwater flood ended, icebergs were no longer transported to the subtropics, but became confined to the subpolar gyre (40-50N; Ruddiman belt). This result suggests that iceberg discharge was probably more effective at weakening NADW formation and the AMOC than catastrophic glacial outburst floods due to freshwater being constantly routed closer to sites of NADW formation. I will end the talk by mentioning some of my other research topics, including the development of MITberg (an iceberg model for MITgcm) and planned Southern Ocean freshwater forcing experiments.