Rapid Cooling and Increased Storminess Triggered by Freshwater in the North Atlantic

Marilena Oltmanns1, Johannes Karstensen2, Kent Moore3 and Simon A Josey1, (1)National Oceanography Centre, Southampton, United Kingdom, (2)Helmholtz Centre for Ocean Res, Kiel, Germany, (3)Univ Toronto, Toronto, ON, Canada
Recent winters have been unique as a result of the rapid and extreme cooling of the subpolar North Atlantic. Traditionally, such cold anomalies have been attributed to a freshwater-forced decrease in deep ocean convection and a subsequent slowdown of the large-scale Atlantic overturning circulation. However, the recent cooling does not fit this paradigm due to the concurrent, record-deep convection. Here, we present a new cooling mechanism, also initiated by freshwater, but one that involves feedbacks with the atmosphere. Combining in-situ observations with remote sensing and atmospheric reanalysis data, we show that increased surface freshening of the subpolar region strengthens the stratification, giving rise to a faster surface cooling in fall and winter. The colder sea surface, in turn, promotes the development of storms and accelerates of the gyre circulation by modulating the wind field. Considering the speed, magnitude and extent of the cooling initiated by recent freshwater anomalies, we expect future increases of the freshwater discharge from Greenland or the Arctic will lead to a continuation of the cooling and an enhanced wintertime storminess.