Denmark Strait Ocean Circulation Variability

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Almansi, Mattia
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Johns Hopkins University
Ocean currents affecting the global climate are sustained by cold and dense water that sinks in the North Atlantic Ocean. A large portion of this water overflows through Denmark Strait, the channel located between Greenland and Iceland. This thesis investigates the physical processes controlling the variability of the circulation in the vicinity of Denmark Strait. As direct measurements are not sufficient to unravel most of these processes, we develop a realistic general circulation model covering the East Greenland shelf and adjacent deep ocean. The model hydrography and circulation agree well with available observations. We find that the yearly mean southward volume flux of dense water is about 30% greater in the presence of mesoscale features known as boluses and pulses. We establish the causal relationship between these features and overflow cyclones observed further south. Most of the cyclones form at the Denmark Strait sill during overflow surges and grow as they move equatorward. A fraction of the cyclones form south of the sill, when anticyclonic vortices formed during high-transport events start collapsing. Finally, the model reveals that the eddy activity north of Denmark Strait regulates the bifurcation of the southward current along the eastern coast of Greenland and the offshore transport of fresh water at the surface.
Denmark Strait, Ocean Circulation, Overflow, Cyclones, Subpolar North Atlantic