The role of wind stress and buoyancy flux in increased poleward ocean heat transport through the Nordic Seas under global warming

The Nordic Seas act as a critical conduit for poleward ocean heat transport (OHT), linking the subpolar North Atlantic to the Arctic Ocean. While climate models consistently project an increase in OHT through the Nordic Seas under global warming, the relative contributions of wind stress and surface buoyancy to this increase are not well understood. In this study, we apply an overriding technique within a coupled climate model to isolate and quantify the impacts of these forcings on the projected increase in OHT. Our perturbation experiments reveal that wind stress and buoyancy flux contribute comparably to the projected OHT enhancement, with wind (buoyancy) forcing being more important at lower (higher) latitudes near 69°N (77°N). Notably, wind stress enhances OHT primarily via a thermodynamical pathway by inducing subsurface warming in the eastern Nordic Seas, which intensifies heat transport by the mean Norwegian Atlantic Current. In contrast, buoyancy forcing enhances OHT through a dynamical pathway. This pathway involves anomalous ocean heat uptake, which reduces sea surface height in the central Nordic Seas. This reduction drives a cyclonic geostrophic response that accelerates the Norwegian Atlantic Current and enhances the northward inflow of warm Atlantic waters. These results highlight the importance of accurately representing both wind and buoyancy forcings in climate models for reliable projections of high-latitude climate change.