Atmospheric Blocking Slows Greenland Glacier Melt

Cooling in the subsurface waters beneath Greenland's Nioghalvfjerdsfjorden Glacier (79NG) from 2018 to 2021 was driven by European atmospheric blocking, which forced changes in the large-scale ocean circulation of the Nordic seas, researchers report, slowing glacial melt, despite ongoing global warming trends. The findings highlight the importance of regional atmospheric dynamics in influencing glacier stability. Understanding these dynamics is key to predicting the future of glaciers like 79NG in a warming climate. The Greenland Ice Sheet has experienced accelerated mass loss in recent decades due to a warming atmosphere and ocean, significantly contributing to global sea-level rise. About half of this loss comes from increased ice discharge from marine-terminating glaciers like 79NG as they retreat and thin, a process predominantly driven by ocean warming, resulting in submarine melting. Since the late 1990s, ocean heat flux has increased, warming subsurface Atlantic Intermediate Water (AIW) that flows below the 79NG ice tongue, enhancing melt rates. However, from 2018 to 2021, direct observations at 79NG revealed a significant water cooling blow the glacier, which reduced ice melt and slowed glacier thinning. Rebecca McPherson and colleagues show that changes in large-scale atmospheric circulation drove this cooling event. McPherson et al. linked this cooling to increased atmospheric blocking, which disrupted normal weather patterns and funneled cold arctic air into the region. The ocean responded by losing more heat to the atmosphere, slowing Atlantic water circulation and cooling the water reaching 79NG. According to the authors, the cooling pattern resembles European blocking, a weather regime associated with a stationary high-pressure system over Europe. Although Atlantic water temperatures are likely to continue to rise with global climate warming, the projected slowdown of the Atlantic Meridional Overturning Circulation (AMOC) could also bring cooler waters to Northeast Greenland's glaciers. "An improved understanding of the connection between the 79NG and the large-scale ocean and atmospheric circulation leads to further advances in our understanding of the response of the 79NG to changing ocean conditions," McPherson et al. write.