Relative sensitivity of the Atlantic meridional overturning circulation to river discharge into Hudson Bay and the Arctic Ocean

Increases in high-latitude river discharge over the 20th century and projected continued increases during the 21st century may have an impact on the Atlantic meridional overturning circulation (AMOC), which could feed back to regional and global climate. Although the general trend in high-latitude river discharge is positive, there is important geographical spread in the trends. While Eurasian rivers draining into the Arctic Ocean show positive trends over the 20th century, rivers draining into Hudson Bay show negative trends since 1964. Here the sensitivity of AMOC to changes in river discharge into Hudson Bay and the Arctic Ocean is studied with an intermediate-complexity Earth system model. It is found that ocean freshening originating from Arctic rivers is more effective in slowing down the AMOC than freshening originating from Hudson Bay rivers, given the same magnitude of freshening in both regions. The lesser impact of Hudson Bay river discharge on AMOC is the result of a buildup of freshwater anomalies in the Labrador Sea affecting the northward flow of the Gulf Stream. This work highlights that not only the freshening magnitude but the region where this freshening takes place is crucial for the AMOC response to altered river discharge climatology.