Rapid submarine melting of the calving faces of West Greenland glaciers

Widespread glacier acceleration has been observed in Greenland in the past few years1–4 associated with the thinning of the lower reaches of the glaciers as they terminate in the ocean5–7. These glaciers thin both at the surface, from warm air temperatures, and along their submerged faces in contact with warm ocean waters8. Little is known about the rates of submarine melting9–11 and how they may affect glacier dynamics. Here we present measurements of ocean currents, temperature and salinity near the calving fronts of the Eqip Sermia, Kangilerngata Sermia, Sermeq Kujatdleq and Sermeq Avangnardleq glaciers in central West Greenland, as well as ice-front bathymetry and geographical positions. We calculate water-mass and heat budgets that reveal summer submarinemelt rates ranging from0.7±0.2 to 3.9±0.8md−1. These rates of submarine melting are two orders of magnitude larger than surface melt rates, but comparable to rates of iceberg discharge. We conclude that ocean waters melt a considerable, but highly variable, fraction of the calving fronts of glaciers before they disintegrate into icebergs, and suggest that submarine melting must have a profound influence on grounding-line stability and ice-flow dynamics. In the past decade, surface melt around Greenland has markedly increased in magnitude and spatial extent, whereas snowfall has increased only slightly12–14. As a result, the ice-sheet mass deficit tripled in the period 1996–2007 (ref. 15). Critically, 50–60% of that loss was caused by an acceleration of the outlet glaciers; the remainder resulting from an increase in surface melt. Hence, glacier acceleration is a significant, if not dominant, response to climate warming. The widespread twoto threefold acceleration of the glaciers cannot be explained solely by enhanced lubrication of the bed from surface meltwater16, for seasonal variations in glacier velocity do not exceed 8–10%, independent of latitude1. Glacier acceleration is instead probably caused by the ungrounding of ice fronts from the bed, which reduces buttressing of inland ice and entrains faster rates of ice flow to the ocean5. To unground glaciers from the bed, they must melt and thin. Warmer air temperatures thin the glaciers from the surface and allow the ice flotation margin to migrate inland. Such surface melting is well documented in Greenland12–14. However, melting can also occur along the submarine termini of the glaciers. A warmer ocean will erode submerged grounded ice and cause the grounding line to retreat. In contrast, we know very little about rates of submarine melting along calving fronts. The only measurements of submarine glacier melting so far have been conducted in Alaska9,10. In August 2008, we deployed two InterOcean S4 conductivity, temperature and depth (CTD)/current meters, a Seabird SBE-19 conductivity and temperature density profiler, and a Lowrance 18C sonar depth sounderwith a global positioning system in the fjords of