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Arctic Sea Ice Meltwater as a Forcing and Feedback on the Atlantic Meridional Overturning Circulation
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DOI：10.1175/JCLI-D-25-0254.1.png)
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Abstract
En 中文
Recent work has shown that the weakening of the Atlantic meridional overturning circulation (AMOC) under anthropogenic climate change is sensitive not only to the amount of atmospheric CO2 increase but also to the rate of CO2 increase. In this work, we explicitly test whether a previously proposed AMOC-sea ice feedback controls the AMOC's sensitivity to the rate of CO2 increase using mechanism-denial experiments in a global climate model. We find that when the AMOC-sea ice feedback is suppressed, the AMOC is nearly insensitive to the rate of CO2 increase, supporting the hypothesis that this feedback is the primary reason for the AMOC's sensitivity to the rate of CO2 increase. Additionally, we show that the reduction of sea ice meltwater in the North Atlantic that is caused by the retreat of Arctic sea ice in a warming climate constitutes a large strengthening forcing on the AMOC, reducing the total amount of AMOC weakening by nearly half. The strong influence of sea ice meltwater on the AMOC both in its role as a forcing and a feedback occurs through the ability of the meltwater to modulate how much surface water mass transformation occurs via ocean heat loss to the atmosphere over the deep convection zones in the North Atlantic. This work demonstrates that Arctic sea ice-AMOC interactions are a first-order control on future AMOC weakening and highlights the importance of constraining present-day sea ice meltwater fluxes to assess their potential counteracting influence on the weakening of Earth's AMOC. SIGNIFICANCE STATEMENT: In this work, we aim to understand how Arctic sea ice influences the weakening of the Atlantic meridional overturning circulation (AMOC) under future anthropogenic greenhouse gas emissions. We find that when Arctic sea ice and the AMOC are allowed to mutually influence each other in a positive feedback cycle, the amount of AMOC weakening is highly sensitive to the rate of CO2 change (even when the CO2 concentration is the same). We also show that the retreat of sea ice under global warming can counteract some of the AMOC weakening induced by CO2 increases. This work highlights how understanding the fundamental mechanisms of AMOC-sea ice interactions is critical for constraining the future weakening of Earth's AMOC.
Keywords:
Sea ice
Feedback
Ocean circulation
Climate change
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