Arctic Marine Heatwaves: Drivers and Feedbacks

Anomalous atmospheric heating initiates most Arctic surface marine heatwaves (MHWs). Sustained anomalous southerly winds drive sea-ice retreat and warm air advection, exposing open water to intense solar radiation that amplifies sea-surface temperature (SST) anomalies.

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Early summer sea-ice melt increases solar absorption, reinforcing the ice-albedo feedback. Meltwater stratification and a shallow, salinity-driven mixed layer confine heat to a thin surface layer, allowing modest heat input to sustain MHWs. Simulations indicate a 20 % increase in MHW duration and intensity.

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In the Barents Sea, high-pressure anomalies over the eastern sector have been linked to MHW onset, while in the Bering Sea MHWs correlate with Alaskan temperatures rather than the Arctic Oscillation. These wind patterns consistently precede sea-ice edge displacement.

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Downward ocean heat fluxes account for over two-fifths of surface MHW dissipation via vertical mixing and entrainment. Upward fluxes from Atlantic-origin subsurface waters contribute one-fifth of surface MHW onsets, driven by wind-induced upwelling, thermohaline convection, and tidal mixing near continental shelves.

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Cloud cover modulates shortwave and longwave radiation at the ocean surface. While low-cloud feedbacks dominate in non-polar oceans, Arctic clouds increase with higher SSTs, potentially offsetting solar shading with reduced albedo and enhanced longwave warming. Recent modest cloud-cover rises have coincided with summer and autumn MHWs, but the net effect remains unresolved.

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The 2007 and 2020 Arctic MHWs absorbed nearly twice the summer solar energy due to exceptionally low ice cover. Model estimates suggest a 20 % intensification of surface MHWs on average, and observed increases in summer and autumn MHW frequency align with modest cloud-cover growth.

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Enhanced surface warming, melt, and stratification create a positive feedback loop that accelerates sea-ice loss. This feedback amplifies the likelihood of future MHWs, potentially altering heat transport pathways and influencing broader Arctic climate dynamics.

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The relative importance of shortwave- versus longwave-driven cloud feedbacks is uncertain. Contributions of mesoscale eddies to MHW onset and decay remain unquantified despite increasingly energetic Arctic conditions. Quantitative estimates of upward heat fluxes and their role in subsurface MHWs are also lacking.

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• “Anomalous atmospheric heating is the primary driver of Arctic surface MHWs61, as elsewhere in the global ocean, but its expression is strongly modulated by sea-ice presence, as discussed below.” — (Nature, 2026)

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• “Sustained anomalous southerly winds are consistently identified as an initiating mechanism21,45,55,56, driving sea-ice retreat and warm air advection65, though the associated pressure patterns differ across studies.” — (Nature, 2026)

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• “Model simulations estimate that this effect lengthens and intensifies surface MHWs by a striking 20% on average61.” — (Nature, 2026)

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• “Such upward ocean heat fluxes contribute to about one-fifth of surface MHW onsets61.” — (Nature, 2026)

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Future work will aim to quantify eddy-driven heat transport, resolve cloud-longwave-SST feedback mechanisms, and improve observational coverage of subsurface heat fluxes to refine predictions of Arctic MHW evolution under continued warming.

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