The Mechanisms of the Atlantic Meridional Overturning Circulation Slowdown Induced by Arctic Sea Ice Decline

Journal Article · Tue Jan 22 00:00:00 EST 2019 · Journal of Climate

DOI:https://doi.org/10.1175/JCLI-D-18-0231.1· OSTI ID:1491612

Liu, Wei ^[1]; Fedorov, Alexey ^[2]; Sévellec, Florian ^[3]

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1. Department of Earth Sciences, University of California Riverside, Riverside, California, and Department of Geology and Geophysics, Yale University, New Haven, Connecticut
2. Department of Geology and Geophysics, Yale University, New Haven, Connecticut
3. Laboratoire d’Océanographie Physique et Spatiale, CNRS, Univ.-Brest IRD, Brest, France, and Ocean and Earth Science, University of Southampton, Southampton, United Kingdom

In this work, 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 ~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.

• Research Organization: Yale Univ., New Haven, CT (United States)
• Sponsoring Organization: USDOE Office of Science (SC); Regents’ Faculty Fellowship; National Science Foundation (NSF); Guggenheim Fellowship; Natural Environment Research Council (NERC); The French National Centre for Scientific Research (CNRS)
• Grant/Contract Number: SC0016538; OCE-1756682; OPP-1741841
• OSTI ID: 1491612
• Alternate ID(s): OSTI ID: 1612621
• Journal Information: Journal of Climate, Journal Name: Journal of Climate Vol. 32 Journal Issue: 4; ISSN 0894-8755
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Meteorology & atmospheric sciences
Arctic
Meridional overturning circulation
Climate models