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Abstract:
To understand and project the implications of enhanced Greenland Ice Sheet mass loss and potential Atlantic Meridional Overturning Circulation weakening it is necessary to determine and overcome challenges in simulating their complex linkages. We discuss the role of the ocean mean state, subpolar gyre circulation, mesoscale eddies and atmospheric coupling in shaping the response of the subpolar North Atlantic Ocean to enhanced Greenland runoff. A suite of eight dedicated 60 to 100-year long model experiments with and without atmospheric coupling, with eddy processes parameterized and explicitly simulated, and with regular and significantly enlarged Greenland runoff is presented. The important role of an interactive atmosphere stands out as being crucial for limiting the AMOC weakening because its response to ocean changes enables a compensating temperature feedback. Further, explicitly simulating mesoscale dynamics yields a more realistic distribution path of the meltwater along the North American coast and into the wider North Atlantic with implications for coastal sea-level rise projections. Underestimating eddy activity in the Labrador Sea may lead to too little or too slow entrainment of meltwater and lack of stratification in the deep convection regions. In this respect we demonstrate where eddy parameterization works quite successfully and where only high resolution (>1/12˚) yields a realistic ocean response. This underlines the necessity to advance scale-aware eddy parameterizations for next-generation climate models.
