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Description: The Labrador Sea is one of the few regions on the planet where the interior ocean can exchange heat directly with the atmosphere via strong, localized, wintertime convection, with possible implications for the state of North Atlantic climate and global surface warming. Using an observationally-constrained ocean adjoint model, we find that annual mean Labrador Sea heat content is sensitive to temperature/salinity changes (1) along potential source water pathways (e.g. the subpolar gyre, the North Atlantic Current, the Gulf Stream) and (2) along the West African and European shelves, which are not significant source water regions for the Labrador Sea. The West African coastal/shelf adjustment mechanism, which may be excited by changes in along-shelf wind stress, involves pressure anomalies that propagate along a coastal waveguide towards Greenland, changing the across-shelf pressure gradient in the North Atlantic and altering heat convergence in the Labrador Sea. We also find that non-local (in space and time) heat fluxes (e.g. in the Irminger Sea, the seas south of Iceland) can have a strong impact on Labrador Sea heat content. Understanding and predicting the state of the Labrador Sea and its potential impacts on North Atlantic climate and global surface warming will require monitoring of oceanic and atmospheric properties at remote sites in the Irminger Sea, the subpolar gyre, and along the West African and European shelf/coast system, among others.