Time-evolving mass loss of the Greenland Ice Sheet from satellite altimetry

Abstract

Abstract. Mass changes of the Greenland Ice Sheet may be estimated by the input-output method (IOM), satellite gravimetry, or via surface elevation change rates (dH /dt). Whereas the first two have been shown to agree well in reconstructing ice-sheet wide mass changes over the last decade, there are few decadal estimates from satellite altimetry and none that provide a time-evolving trend that can be readily compared with the other methods. Here, we interpolate radar and laser altimetry data between 1995 and 2009 in both space and time to reconstruct the evolving volume changes. A firn densification model forced by the output of a regional climate model is used to convert volume to mass. We consider and investigate the potential sources of error in our reconstruction of mass trends, including geophysical biases in the altimetry, and the resulting mass change rates are compared to other published estimates. We find that mass changes are dominated by surface mass balance (SMB) until about 2001, when mass loss rapidly accelerates. The onset of this acceleration is somewhat later, and less gradual, compared to the IOM. Our time-averaged mass changes agree well with recently published estimates based on gravimetry, IOM, laser altimetry, and with radar altimetry when merged with airborne data over outlet glaciers. We demonstrate that, with appropriate treatment, satellite radar altimetry can provide reliable estimates of mass trends for the Greenland Ice Sheet. With the inclusion of data from CryoSat-2, this provides the possibility of producing a continuous time series of regional mass trends from 1992 onward.

A representative density profile of the North Greenland snowpack

“…The profile is available at a resolution of 0.1 cm and only has to be rescaled according to accumulation rate. Thus it is ready to act as a benchmark for snowpack models or be applied for the conversion of volume to mass and the detection of strong density gradients as potential reflectors in remote sensing (compare e.g., Hurkmans et al, 2014).…”

Simultaneous solution for mass trends on the West Antarctic Ice Sheet

“…They are useful for helping to partition a height change between the different processes that can cause that change. For example, a long wavelength variation in height that spans different basins is likely associated with SMB, whereas a localised change that shows some relationship to surface velocity is likely associated with ice dynamics (Hurkmans et al, 2014). Hence, mass loss due to ice dynamics was assumed to mostly take place in areas of faster flow (Hurkmans et al, 2014).…”

“…For example, a long wavelength variation in height that spans different basins is likely associated with SMB, whereas a localised change that shows some relationship to surface velocity is likely associated with ice dynamics (Hurkmans et al, 2014). Hence, mass loss due to ice dynamics was assumed to mostly take place in areas of faster flow (Hurkmans et al, 2014). A "soft" constraint was thus placed on elevation rates due to ice dynamics such that it is small (1 mm yr −1 ) in areas of low velocities and can be large (up to 15 m yr −1 ) for velocities greater than 10 m yr −1 .…”

A simple equation for the melt elevation feedback of ice sheets

“…In reality, ice dynamics of course play an important role in the ice sheet mass balance: radar (ERS-2) and laser (ICESat) altimetry observations show that mass changes in Greenland were dominated by changes in the surface mass balance (SMB) between 1995 and 2001, and both SMB and dynamics contributed equally to mass loss from the Greenland Ice Sheet between 2001 and 2009 (Hurkmans et al, 2014). Fürst et al (2015) estimate that 40 % of the recent loss (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010) is due to an increase in ice dynamic discharge, 60 % due to changes in the surface mass balance.…”