The Mechanisms of the Atlantic Meridional Overturning Circulation Slowdown Induced by Arctic Sea Ice Decline
|Liu Wei1, 2, Fedorov Alexey2, Sevellec Florian3, 4
|1 : Univ Calif Riverside, Dept Earth Sci, Riverside, CA 92521 USA.
2 : Yale Univ, Dept Geol & Geophys, New Haven, CT 06520 USA.
3 : Univ Brest IRD, CNRS, Lab Oceanog Phys & Spatiale, Brest, France.
4 : Univ Southampton, Ocean & Earth Sci, Southampton, Hants, England.
|Journal Of Climate (0894-8755) (Amer Meteorological Soc), 2019-02 , Vol. 32 , N. 4 , P. 977-996
|WOS© Times Cited
|Arctic, Meridional overturning circulation, Climate models
We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next similar to 100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these buoyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection.