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Impact of fjord dynamics and glacial runoff on the circulation near Helheim Glacier

Abstract

Submarine melting is an important contributor to the mass balance of tidewater glaciers in Greenland, and has been suggested as a trigger for their widespread acceleration. Our understanding of this process is limited, however. It generally relies on the simplified model of subglacial discharge in a homogeneous ocean, where the melting circulation consists of an entraining, buoyant plume at the ice edge, inflow of ocean water at depth, and outflow of a mixture of glacial meltwater and ocean water at the surface. Here, we use oceanographic data collected in August 2009 and March 2010 at the margins of Helheim Glacier, Greenland to show that the melting circulation is affected by seasonal runoff from the glacier and by the fjord’s externally forced currents and stratification. The presence of light Arctic and dense Atlantic waters in the fjord, in particular, causes meltwater to be exported at depth, and influences the vertical distribution of heat along the ice margin. Our results indicate that the melting circulation is more complex than hypothesized and influenced by multiple external parameters. We conclude that the shape and stability of Greenland’s glaciers may be strongly influenced by the layering of the Arctic and Atlantic waters in the fjord, as well as their variability.

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Figure 1: Summer 2009 and winter 2010 surveys of Sermilik Fjord.
Figure 2: Atlantic and Arctic waters in Sermilik Fjord.
Figure 3: Layered circulation at the edge of Helheim Glacier.
Figure 4: Impact of glacial runoff and melt on the fjord’s waters.
Figure 5: Particulate discharge at depth from Helheim Glacier in summer 2009.

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Acknowledgements

We thank M. Duchin and I. Menn from Greenpeace, P. Willcox (captain), A. Sørensen (ice pilot) and the entire crew of the M/V Arctic Sunrise, and Greenpeace International for their support in making the summer measurements in Sermilik Fjord; J. Ryder, J. Kemp and his group for logistic planning of the fieldwork; D. Torres, A. Ramsey, and S. Worrilow for instrument preparation and support. F.S. acknowledges support from Woods Hole Oceanographic Institution’s Ocean and Climate Change Institute’s Arctic Research Initiative and from NSF OCE 0751554 and ARC 0909373, and G.S.H. and L.A.S. acknowledge support from NASA’s Cryospheric Sciences Program.

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F.S., D.A.S., R.G.C. and G.S.H. conceived the study, F.S., D. A. S., R.G.C, K.V., L.A.S. and G.S.H. participated in the collection of oceanographic data in Sermilik Fjord, and F.S., D.A.S. and C.C. were responsible for the analysis and interpretation.

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Correspondence to Fiammetta Straneo.

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The authors declare no competing financial interests.

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Straneo, F., Curry, R., Sutherland, D. et al. Impact of fjord dynamics and glacial runoff on the circulation near Helheim Glacier. Nature Geosci 4, 322–327 (2011). https://doi.org/10.1038/ngeo1109

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