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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.
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This content will become publicly available on July 15, 2026
Response of the Atlantic Meridional Overturning Circulation to a Sudden Surface Warming and Amplification of the Hydrological Cycle
An idealized ice–ocean model is used to study the time-dependent Atlantic meridional overturning circulation (AMOC) responses to a sudden uniform surface warming and/or an amplified evaporation minus precipitation (E−P) forcing. At transient time scales, the AMOC initially weakens in response to both types of forcing as a result of buoyancy gain in the North Atlantic, but the amplified E−P response is an order of magnitude smaller when its amplitude is chosen based on the Clausius–Clapeyron scaling, consistent with its weaker initial buoyancy flux anomaly. At equilibrium, the AMOC here weakens under warming, contrasting with previous idealized modeling studies. The difference is attributed to a larger role of North Atlantic warming (acting to weaken the AMOC) and a weaker role of reduced brine rejection around Antarctica (acting to deepen and strengthen the AMOC). When E−P forcing is amplified, the AMOC strengthens, qualitatively consistent with a previously proposed passive response that predicts an enhancement of the existing salinity pattern in equilibrium, although the amplification of the salinity contrast is significantly damped by a negative salt advection feedback. For a small-amplitude change in both temperature and E−P, the AMOC response can be approximated by the linear combination of the individual responses. However, large-amplitude warming and amplified E−P forcing can lead to a positive salt advection feedback that collapses the AMOC in our simulations. To understand why the sign of the salt advection feedback varies across different simulations, its multifaceted roles are further investigated using box model theories, and their relevance to comprehensive models is discussed.
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- Award ID(s):
- 1846821
- PAR ID:
- 10643553
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 38
- Issue:
- 14
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 3261 to 3276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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