Ocean Regulation Controls Ice Sheet Mass Loss in the Southeast Greenland Ice Sheet

During the years 2003 and 2005, the southeast outlet glaciers of the GrIS underwent dramatic thinning and the ice sheet significantly retreated; surprisingly in 2006, the acceleration rates of the two largest outlet glaciers of the ice sheet decreased, causing the ice sheet to cease thinning and re-advance. In this paper, Murray et al. (2010) explore this synchronous acceleration and thinning of the ice sheet, and propose that regional factors have the greatest impact on these ice sheet-ocean interactions. They conclude that the ice sheet mass loss in the southeast GrIS is primarily caused by the warming and cooling of the coastal waters around the coastal glaciers. —Sachi Singh
Murray, K., Scharrer, K. , James, T. D., Dye, S. R., Hanna, E., Booth, A. D., Selmes, N., Luckman, A., Hughes, A. L. C., Cook, S., Huybrechts, P. 2010. Ocean regulation hypothesis for glacier dynamics in southeast Greenland and implications for ice sheet mass changes. doi:10.1029/2009JF001522.

Atmospheric warming and ocean/fjord temperatures both significantly affect glacier dynamics. Atmospheric warming can lead to increased sea-surface temperatures. which enhance basal sliding and increase glacier speeds. Consequently, the meltwater can enter the crevasses of the glaciers and increase the rate of glacier calving. Similarly, warm surface waters can reduce the extent of fjord ice and undermine the integrity of the ice melange (which are small pieces of calved ice and sea ice), which can eventually lead to higher rates of calving and faster flow conditions. In the paper, the authors analyzed the flow speeds, surface elevation, and calving front positions for tidewater terminating glaciers in southeast Greenland to determine the relationship between oceanic processes and glacier dynamics. From the analysis of the sea-surface temperatures, they found the the glacier speed-up of 2003 was not caused by the increase in surface meltwater and basal sliding; instead, it was caused by the warm surface waters that were brought to the southeast coast of Greenland by the Irminger Current (IC). The IC—which brings warm, high salinity water from the Atlantic—bifurcates to the west of Iceland, causing one of its branches to flow southwards along the southeast coast of Greenland; the East Greenland Coastal Current (EGCC)—which brings fresh, cold water to the coast—flows right by the IC, along the landward side of the continental shelf. The authors found that the 2003 speed-up of glaciers—associated with warm IC and weak EGCC—led to a large deposition of cold water into the EGCC; this increased ice discharge into the EGCC strengthened the cold current, decreased the sea-surface temperatures and subsequently, slowed down the glaciers in 2006. Thus, the authors conclude that the ice sheet‘s input provided a negative feedback to the EGCC, which controlled the ice sheet mass loss and re-stabilized the coastal glaciers. 

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