Dynamic and Steric Sea-level Changes due to a Collapsing AMOC in the Community Earth System Model

Abstract. A collapse of the Atlantic Meridional Overturning Circulation (AMOC) leads to a redistribution of dynamic sea level (DSL) across the global ocean surface. Here, we investigate AMOC-induced DSL and steric sea-level responses using the Community Earth System Model and two stand-alone ocean configurations (strongly eddying and parameterising eddy effects) with the Parallel Ocean Program. For our analysis, we employ various quasi-equilibrium freshwater hosing experiments in which AMOC collapses were reported. As the AMOC begins to collapse, the DSL substantially rises over the Atlantic Ocean and Arctic Ocean, with the largest DSL changes reaching 6 mm yr^-1 over the North Atlantic Ocean. In densely-populated coastal regions along the North Atlantic Ocean, DSL trends of up to 4 mm yr^-1 are found, potentially doubling local sea-level rise rates under an AMOC collapse scenario. Given the quasi-equilibrium approach, the hosing contribution to DSL trends is relatively small for periods of ≤ 100 years but becomes increasingly important over longer timescale. Moreover, an AMOC collapse increases the radiative imbalance at the top of the atmosphere up to +0.5 W m^-2, with the excess heat being absorbed by the ocean, leading to more than 20 cm of global mean thermosteric sea-level rise. These results highlight the potential value of accounting for an AMOC collapse scenario when developing or applying sea-level rise projections for the North Atlantic Ocean.