Cross-Isobath Freshwater Exchange Within the North Atlantic Subpolar Gyre

The amount of cross-isobath freshwater exchange within the North Atlantic subpolar gyre is estimated from numerical modelling simulations. A regional configuration of the Nucleus for European Modelling of the Ocean model is used to carry out three simulations with horizontal resolutions of 1/4 degrees, 1/12 degrees, and 1/4 degrees with a 1/12 degrees nested domain. Freshwater transport is calculated across five isobaths in six regions for three distinct water masses. Fresh Polar Water is only transported offshore from the western coast of Greenland and the southern coast of Labrador; other regions have onshore transport of freshwater or little offshore transport. The salty water masses of Irminger and Labrador Sea Water typically have onshore transport, acting to promote subsurface freshening of the Labrador Sea. The freshwater transport via the Polar Water mass experiences a large degree of seasonal variability, while the Irminger and Labrador Sea Water masses do not. Decomposing the freshwater transport into the mean and turbulent components indicates that most regions and water masses have stronger freshwater transport associated with the mean flow while the turbulent flow in often the opposite direction. The only water mass and region where the mean and turbulent freshwater transport act in the same direction is Polar Water along the western margin of Greenland. Model resolution plays an important role in determining cross-isobath exchange as our results from an identically forced simulation at 1/4 degrees has reduced seasonal cycles, reduced transport, and sometimes transport in the opposite direction when compared against the 1/12 degrees resolution simulations. Plain Language Summary The Labrador Sea, between Greenland and Canada, is a region where deep water is formed, a crucial component in the oceanic transport of heat between the equator and the poles. An input of freshwater can interrupt this process by making deep water more difficult to produce. While we know the Labrador Sea receives freshwater from the surrounding currents, we are not confident where, and how much, freshwater leaves the boundary of the Labrador Sea to enter the interior region. We explore this using numerical simulations in a region where real data collection is difficult due to extreme ocean conditions. Our simulations suggest that the west coast of Greenland is the region where most of the freshwater leaves the boundary current and enters the deeper basin. The other regions either have freshwater transported toward the coast or very little transport to begin with. We also investigated the short-lived turbulent transport of freshwater which was generally flowing from the coastal region to the deep basin, often acting opposite the long-term flow.