Collaborative Research: Shelf-Basin Exchange South of Denmark Strait: Forcing, Dynamics, and Large-Scale Impact

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The Irminger Sea, situated between southern Greenland and the Reykjanes Ridge, is a critically important area where the Arctic Sea first meets the North Atlantic Ocean. South of the Denmark Strait, a sharp front is formed where cold, fresh outflowing Arctic water meets the warm, salty subtropical-origin water. This front and its associated jet, the East Greenland/Irminger Current, act as the main pathway that recirculating subtropical-origin Arctic water is exported to the North Atlantic. With the stress of the down-front barrier winds adjacent to the Greenland plateau in addition to the instability and time-variability of both the front and the Irminger Current, intense shelf-basin exchange with the open Atlantic occurs in this region. As part of this exchange process, dense shelf water cascades over the shelf-break to form a "Spill Jet" which resides below the East Greenland/Irminger Current. This results in substantial sinking, which occurs downstream in the Labrador Sea and impacts the sub-polar gyre and the meridional overturning circulation to northern freshwater sources. Currently, scientists have a poor understanding of this complex shelf-break current system, and thus are unsure of its transport, freshwater flux, seasonal evolution, and the nature and dynamics of the mesoscale variability that lead to the cross-stream exchange of mass and properties. Through a joint observational/modeling study, oceanographers from Woods Hole Oceanographic Institution and Johns Hopkins University propose to quantify the hydrodynamic instability and atmospheric forcing that drive shelf-basin exchange to occur east of Greenland. By examining the mean and seasonally varying transport, structure, and kinematics of the East Greenland/Irminger Current system and determining the nature and dynamics of the mesoscale variability that leads to shelf-basin exchange, they will be able to explore how the impact of shelf-basin exchange on the sub-polar North Atlantic has changed in the last few decades and how it may evolve in the future. The broader impacts of this study address the concern about the sensitivity of the North Atlantic meridional overturning circulation with respect to northern freshwater sources. Approximately one half of the total Arctic export of freshwater passes east of Greenland and meets the open Atlantic in the proposed study area, therefore understanding the dynamics of the shelf-basin exchange in this region is essential to potentially predict the response of the North Atlantic to future changes in climate. This research includes funding to support educational outreach including activities in a remote location in southern Greenland, as well as science center exhibits in the United States. Funding is also included to support education and training at both the graduate and undergraduate level.