Pathways and impacts of increased Greenland and Arctic freshwater fluxes to the Subpolar North Atlantic

In the coming decades, climate change is expected to lead to increasing freshwater input to the subpolar North Atlantic from Greenland and the Arctic. This could affect the ocean circulation in the region, and potentially the Atlantic Meridional Overturning Circulation (AMOC).Greenland and Arctic origin waters initially enter the coastal and shelf regions of Greenland and Canada, where they are transported by narrow boundary currents. Observational studies and regional simulations have shown that exchanges between the shelf region and the open ocean are restricted to a few areas. This constrains where, how much, and at which timescales, additional freshwater may affect the interior subpolar North Atlantic.The potential effects of Greenland melt on the AMOC is often tested in climate models via hosing experiments, in which large volumes of freshwater are released across broad areas of the North Atlantic. While most hosing experiments release freshwater uniformly in that region to understand the mechanisms and impacts of an AMOC slowdown, a few targeted freshwater release experiments have also been carried out around Greenland to more realistically assess how Greenland melt might affect the ocean circulation.It is however unclear whether the resolution of these models allows to adequately represent the pathways of the added freshwater. Moreover, the traditional understanding of a direct link between convection in the Subpolar Gyre and the AMOC has been challenged, highlighting the need to also assess the effect of the added freshwater on the circulation and hydrography of the subpolar North Atlantic.Here we use results from hosing experiments carried out in the MPI-ESM coupled climate model as part of the NAHosMIP project (Jackson et al 2023) to examine how the added freshwater circulates in the subpolar North Atlantic and affects the region's circulation and hydrography. We compare the Greenland focused and uniform hosing experiments to investigate how the hosing location affects these results. We then evaluate these findings against observations and results from high-resolution regional simulations to determine whether targeted hosing experiments can indeed help understanding the impact of future increases in freshwater input to the subpolar North Atlantic, identify potential limitations, and how they could be addressed.----Jackson, L. C., Alastrué de Asenjo, E., Bellomo, K., Danabasoglu, G., Haak, H., Hu, A., Jungclaus, J., Lee, W., Meccia, V. L., Saenko, O., Shao, A., and Swingedouw, D.: Understanding AMOC stability: the North Atlantic Hosing Model Intercomparison Project, Geoscientific Model Development, 16, 1975–1995, https://doi.org/10.5194/gmd-16-1975-2023, 2023.

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