Changes in the firn structure of the western Greenland Ice Sheet caused by recent warming

The Cryosphere

D.Mair¹  B.Noël¹  S.de la Peña¹  I. M.Howat¹  P. W.Nienow¹  M. R.van den Broeke¹  S. F.Price¹  E.Mosley-Thompson¹  A. J.Sole¹ 

DOI  :  10.5194/tc-9-1203-2015

学科分类：地球科学(综合)

来源: Copernicus Publications

【 摘 要 】

Atmospheric warming over the Greenland Ice Sheet during thelast 2 decades has increased the amount of surface meltwater production,resulting in the migration of melt and percolation regimes to higheraltitudes and an increase in the amount of ice content from refrozenmeltwater found in the firn above the superimposed ice zone. Here we presentfield and airborne radar observations of buried ice layers within thenear-surface (0–20 m) firn in western Greenland, obtained from campaignsbetween 1998 and 2014. We find a sharp increase in firn-ice content in theform of thick widespread layers in the percolation zone, which decreases thecapacity of the firn to store meltwater. The estimated total annual icecontent retained in the near-surface firn in areas with positive surfacemass balance west of the ice divide in Greenland reached a maximum of74 ± 25 Gt in 2012, compared to the 1958–1999 average of 13 ± 2 Gt,while the percolation zone area more than doubled between 2003 and 2012.Increased melt and column densification resulted in surface loweringaveraging −0.80 ± 0.39 m yr⁻¹ between 1800 and 2800 m in theaccumulation zone of western Greenland. Since 2007, modeled annual melt andrefreezing rates in the percolation zone at elevations below 2100 m surpassthe annual snowfall from the previous year, implying that mass gain in theregion is retained after melt in the form of refrozen meltwater. If currentmelt trends over high elevation regions continue, subsequent changes in firnstructure will have implications for the hydrology of the ice sheet andrelated abrupt seasonal densification could become increasingly significantfor altimetry-derived ice sheet mass balance estimates.

【 授权许可】

Unknown