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Structure, variability, and dynamics of the West Greenland Boundary Current System

Astrid Pacini, Ph.D., 2022
Robert Pickart, Advisor

This thesis characterizes the West Greenland Boundary Current System near Cape Farewell across a range of spatio-temporal scales using data from the Overturning in the Subpolar North Atlantic Program (OSNAP) from 2014-18. We present the first observations of the year-round structure, composition, and seasonality of the different components of the boundary current system. Both air-sea buoyancy forcing and remote wind forcing dictate the seasonality. At synoptic timescales, strong, mid-depth intensified cyclones generated at Denmark Strait enhance the transport of overflow water, while extensive meandering of the surface-intensified flow is driven by baroclinic instability. This process spawns small eddies that are able to account for the entirety of wintertime heat loss within the Labrador Sea. The meandering also triggers the formation of the well-known Irminger Rings. Wind-driven upwelling is common along the West Greenland shelfbreak, driven by forward Greenland tip jets that develop in response to passing low pressure systems. The resulting secondary circulation fluxes a significant amount of freshwater from the shelf to the basin, which can explain the observed lack of ventilation in the eastern Labrador Sea. Together, this thesis documents previously unobserved interannual, seasonal, and synoptic-scale variability and dynamics within the Labrador Sea boundary current system.