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Surface Activity on the South-Central Greenland Ice Sheet
Reference
Jezek, K.C. 2012. Surface elevation and velocity changes on the south-central Greenland ice sheet: 1980-2011. Journal of Glaciology 58: 1201-1211.

Background
Satellite altimeter measurements of ice-sheet elevation began in 1975; and the author writes that Seasat and Geosat (1975-86) altimeter data revealed that "the southern half of Greenland was thickening by ~0.20 0.06 m/year, with a possible increase in thickening rate to 0.28 0.02 m/year for the later part of the record." Subsequently, he says that Johannessen et al. (2005) analyzed 1992-2003 data from the two European Remote-sensing Satellites to show that ice thickness increased on average by 0.064 0.2 m/year at elevations above 1500 m," while Zwally et al. (2011) "found continued interior ice-sheet growth, but that surface melting and accelerated flow increased thinning rates at the ice-sheet margins."

What was done
Bringing still more data to bear upon the issue, Jezek extended through 2011 "an ice-sheet elevation and surface velocity record across three measurement networks established in south-central Greenland by The Ohio State University in 1980/81," where "surface parameters are derived from repeat GPS in situ observations," and where elevations are "measured by airborne laser altimetry and by the Ice, Cloud and land Elevation Satellite (ICESat)."

What was learned
The Ohio State University (USA) researcher reports that the most recent data show that thinning rates are slowing at several sites just east of the divide, and that the elevation at the divide continues to increase.

What it means
"These results," in the words of Jezek, "show that the Greenland ice sheet is changing from terminus to divide," and that "measurement strategies designed to predict future changes and to estimate volumetric changes across the ice sheet need to appropriately cover the entirety of the ice sheet [italics added]."

References
Johannessen, O.M., Khvorostovsky, K., Miles, M.W. and Bobylev, L.P. 2005. Recent ice-sheet growth in the interior of Greenland. Science 310: 1013-1016.

Zwally, H.J., Jun, L.I., Brenner, A.C., Beckley, M., Cornejo, H.G., Dimarzio, J., Giovinetto, M.B., Neumann, T.A., Robbins, J., Saba, J.L., Donghui, Y.I. and Wang, W. 2011. Greenland ice sheet mass balance: distribution of increased mass loss with climate warming: 2003-07 versus 1992-2002. Journal of Glaciology 57: 88-102.

Reviewed 10 July 2013