Abstract
Water mass transformation in the Nordic and Barents Seas, triggered by air-sea heat fluxes, is an integral component of the Atlantic Meridional Overturning Circulation (AMOC). These regions are undergoing rapid warming, associated with a retreat in ice cover. Here we present an analysis covering 1950−2020 of the spatiotemporal variability of the air-sea heat fluxes along the region’s boundary currents, where water mass transformation impacts are large. We find there is an increase in the air-sea heat fluxes along these currents that is a function of the currents’ orientation relative to the axis of sea-ice change suggesting enhanced water mass transformation is occurring. Previous work has shown a reduction in heat fluxes in the interior of the Nordic Seas. As a result, a reorganization seems to be underway in where water mass transformation occurs, that needs to be considered when ascertaining how the AMOC will respond to a warming climate.
Highlights
Water mass transformation in the Nordic and Barents Seas, triggered by air-sea heat fluxes, is an integral component of the Atlantic Meridional Overturning Circulation (AMOC)
The winter mean turbulent heat flux is typically small over ice covered regions, as a result of the insulating properties of sea ice, and increases rapidly across the marginal ice zones with maxima in the northern Greenland Sea, in the vicinity of Svalbard, as well as in the Barents Sea[10,28,33]
This relatively modest increase in integrated flux is because of the dipolar nature (Fig. 4c) of the anomalies along the current. This is confirmed by a moving window trend for this time series of 4−10 W/m2/decade for start dates from the 1950s−1990s (Fig. 5f). These results confirm that the relative orientation of sea-ice retreat versus the current axis is critical for characterizing the changes in the surface heat fluxes
Summary
Water mass transformation in the Nordic and Barents Seas, triggered by air-sea heat fluxes, is an integral component of the Atlantic Meridional Overturning Circulation (AMOC) These regions are undergoing rapid warming, associated with a retreat in ice cover. Within the Nordic and Barents Seas, there exist three major boundary currents where water mass modification occurs (Fig. 1): the East Greenland Current (EGC) that flows southward along the East Greenland shelfbreak/upper-slope from Fram Strait to Denmark Strait[17,18]; the Norwegian Atlantic Current that flows northward through Fram Strait into the Nansen Basin as the Svalbard Branch (SB)[7,8]; and the Barents Sea Branch (BSB) that progresses from the Norwegian Sea through the Barents Sea towards Novaya Zemlya[6,19,20]. Within the Barents Sea, the retreat of winter sea ice has resulted in profound changes in the climate—an Atlantification of the region[30]
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