Early Winter Triggering of the Maud Rise Polynya

What triggers Maud Rise polynya, a large opening in the winter Antarctic sea ice, is still debated. We show that the upcoming opening of all Maud Rise polynyas can be detected in early winter up to four months ahead, especially since the 2002 expansion in satellite observations. In all polynya years, continuous anomalous sea ice thinning begins in May, caused by atmospheric and oceanic forcings. Dynamically, an anomalous cyclonic circulation in the atmosphere and the ocean strengthens the Weddell Gyre and exerts anomalously intense stresses on the ice. Thermodynamically, the warm water advected by the intensified circulation, and most importantly entrained into the mixed layer, thins the ice from below at the beginning of the freezing season, preconditioning the region for a polynya event months later. This four-month-ahead pattern enables early predictions of the polynya, and improved expedition planning and sensor deployment.