Sea-ice retreat may invigorate the weakening Atlantic Meridional Overturning Circulation

Due to rapidly rising air temperature over the Arctic and subarctic regions, the ocean-to-air turbulent (i.e., sensible and latent) heat flux over the Greenland, Iceland, and Norwegian Seas (GINS) has diminished (i.e., less cooling of the surface ocean) steadily during the satellite period (i.e., since the 1970s). This may lead to a reduction of deep ocean convection in the region, and thus a slowdown of the Atlantic Meridional Overturning Circulation (AMOC). However, a new study published in Nature Communications argues exactly the opposite is happening. The study analyzed the ocean-to-air turbulence heat flux along the major boundary currents in the GINS (i.e., the East Greenland Current, the Svalbard Branch, and the Barents Sea Branch) using the European Centre for Medium-Range Forecasts reanalysis version 5 (ERA5) for the period of 1950-2020. The study found that the ongoing sea-ice retreat in the regions has exposed the boundary currents in direct contact with the atmosphere. As a result, the ocean-to-air turbulent heat flux has significantly increased (i.e., an increase in ocean cooling) along the pathways of the regional boundary currents. Since the deep ocean convection in these regions occurs primarily along the boundary currents, the increased buoyancy loss along the pathways of the boundary currents results in an increase in deep ocean convection. This may potentially lead to an invigoration of the AMOC, which is believed to be weakening in recent periods due to both anthropogenic forcings (e.g., increased Greenland ice-water discharge) and natural climate variability associated with the North Atlantic Oscillation. One caveat of this study is that the conclusion is solely based on a turbulence heat flux analysis. No hydrographic evidence was provided to back up the hypothesis.

Figure 1 from Moore et al. (2022): The bathymetry of the Nordic and Barents Seas. The domains associated with the East Greenland Current (EGC), the Svalbard Branch (SB), and the Barents Sea Branch (BSB) are shown in black with distances along the direction of the current flow indicated.

Moore, G.W.K., Våge, K., Renfrew, I.A. Pickart, R.S. (2022). Sea-ice retreat suggests re-organization of water mass transformation in the Nordic and Barents Seas. Nature Communications, 13, 67.

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