HR: 0800h
AN: C11A-0082    [Abstracts]
TI: Greenland Ice Sheet Surface Temperature, Melt, and Mass Loss - 2000 to 2006
AU: * Hall, D K
EM: dorothy.k.hall@nasa.gov
AF: NASA / Goddard Space Flight Center, Code 614.1 NASA / GSFC, Greenbelt, MD 20771, United States
AU: Williams, R S
EM: rswilliams@usgs.gov
AF: USGS, USGS / Woods Hole Science Center, Woods Hole, MA 02543, United States
AU: Luthcke, S B
EM: scott.b.luthcke@nasa.gov
AF: NASA / Goddard Space Flight Center, Code 698 NASA / GSFC, Greenbelt, MD 20771, United States
AU: DiGirolamo, N E
EM: nicolo.e.digirolamo@nasa.gov
AF: Science Systems and Applications, Inc., 10210 Greenbelt Road, Lanham, MD 20706, United States
AB: A daily-time series of clear-sky surface temperature has been compiled of the Greenland Ice Sheet (GIS) using the 1-km resolution, clear-sky land-surface temperature (LST) standard-data product from the Moderate- Resolution Imaging Spectroradiometer (MODIS), from 2000 to 2006. Surface temperature is important because it is a sensitive indicator of surface-melt timing and duration. We also use the Gravity Recovery and Climate Experiment (GRACE) mass concentration, or mascon, solution data to study mass change on the GIS in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the last six years of the study period by ~0.27 deg C per yr. The LST increase was especially notable in the northern half of the ice sheet during the winter months and at higher elevations. Over the course of the study period, most of the six major drainage basins of the GIS experienced longer melt seasons, and a stable or later start and end of the melt season; however basins 4 and 5, in southern Greenland, showed dramatically earlier initiation of the melt season by up to 18 and 22 days, respectively. While none of the observed trends is statistically significant in part due to the brevity of the record, they are consistent with trends seen using a variety of other observations. End-of- melt-season data for 2007 will also be presented. Furthermore, we show that when less than 1 percent of the ice-sheet experienced surface melt, rapid (less than 15 days) and sustained mass loss below 2000-m elevation is triggered in 2004 and 2005 as recorded by GRACE. Below 2000 m in 2004 and 2005, the ice sheet lost about 321 and 444 Gt of mass, respectively, and experienced more melting in 2005 as compared to 2004. After cessation of surface melt (in 2003, 2004 and 2005), GRACE data show an increase in mass from accumulation, with a delay of less than 30 days. The result that initiation of large-scale surface melt is followed rapidly by mass loss supports other work showing that surface meltwater is flowing rapidly to the base of the ice sheet causing acceleration of outlet glaciers. This result highlights the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.
DE: 0758 Remote sensing
DE: 0776 Glaciology (1621, 1827, 1863)
SC: Cryosphere [C]
MN: 2007 Fall Meeting