The atmosphere-land/ice-ocean system in the region near the 79N Glacier in Northeast Greenland: Synthesis and key findings from GROCE

Abstract. The Greenland Ice Sheet has steadily lost mass over the past decades, presently representing the second-largest single contributor to global sea-level rise. Even the glaciers draining the Northeast Greenland ice stream have been observed to retreat and thin. Here, we present a comprehensive study of processes affecting and being affected by the mass balance of marine terminating and peripheral glaciers in Northeast Greenland. Our focus is on the 79N Glacier (79NG), which hosts Greenland’s largest floating ice tongue. We provide new insight into the ice surface melt, ice mass balance, glacier dynamics, regional solid earth response, ocean-driven basal melt and the consequences of meltwater discharge into the ocean. Our study is based on observations, remote sensing and simulations with numerical models of different complexity, most of them originating from the Greenland Ice Sheet–Ocean Interaction Experiment (GROCE). We find the overall negative climatic mass balance of the 79NG to co-vary with summertime volumes of supraglacial lakes, and show the spatial pattern of overall negative ice mass balance for NE Greenland to be mirrored by the pattern of glacial isostatic adjustment. We find near coastal mass losses of both marine terminating and peripheral glaciers in NE Greenland to be of similar magnitude in the last decade. In contrast to the neighboring Zachariae Isstrøm, the 79NG – despite experiencing massive thinning of the floating tongue – has resisted an acceleration of ice discharge across the grounding line due to buttressing imposed by lateral friction of the 70 km-long ice tongue in the narrow glacial fjord. Observations and models employed in this study are consistent in terms of melt rates occurring below the floating ice tongue. Our results suggest the multidecadal warming of Atlantic Intermediate Water flowing into the cavity below the ice tongue – supplied by the recirculating branch of the West Spitsbergen Current in Fram Strait – to be the main driver of the recent major increase in basal melt rates. We find the melt water leaving the cavity toward the ocean at subsurface levels to quickly dilute on the wide shelf. The study concludes by summarizing important estimates of changes to the state of the atmosphere, ice, land and ocean domains.