Towards quantifying the contribution of the Antarctic ice sheet to global sea level change

Abstract

Abstract. At present, the mass balance of the Antarctic Ice Sheet (AIS) and its contribution to global sea level change are poorly known. Current methods to determine AIS mass balance as well as the inherent uncertainties are discussed. Special emphasis is placed on the increasingly important role of regional atmospheric climate models, which can reduce the uncertainties in surface accumulation, the correction for the firn layer depth and density in ice thickness calculations and moreover help in interpreting surface elevation changes in terms of accumulation and firn density variability. Some recent advances in these fields of research are presented.

Roles of marine ice, rheology, and fracture in the flow and stability of the Brunt/Stancomb‐Wills Ice Shelf

“…Ice shelf thickness is calculated from these elevations assuming hydrostatic equilibrium and adjusting for the presence of firn. No detailed firn density profiles could be found for the BSW system, we therefore base our firn estimates on van den Broeke [2006, 2008]. These studies, which combine regional climate and firn densification models, predict that the 830 kg m −3 firn density depth to be 55–65 m for the BSW area.…”

“…We therefore adjust ice shelf thickness by assuming a uniform firn layer of 65 m, at the density of 830 kg m −3 . In this approximation, setting firn depth at the higher end of the 55–65 m simulated by van den Broeke [2006, 2008] should compensate for the lower density higher in the firn column. The density of ice mélange areas should be close to that of the rest of the ice shelf as fully consolidated marine ice, the main component there in addition to firn and ice shelf fragments, has the same density as meteoric ice within measurement error [ Oerter et al , 1994].…”

Recent Antarctic ice mass loss from radar interferometry and regional climate modelling

“…Earlier work assumed a constant firn depth correction. We calculate H from a firn densification model 16 driven by surface density using 25-year-average air temperature, snow accumulation and wind speed from RACMO2/ANT. H varies from 0 to 20 m. Its precision is 2-3 m on the basis of a comparison with firn core data at the critical densities of 550 and 880 kg m −3 .…”

“…For surface elevation, we use a new digital elevation model (DEM) combining precise laser altimeter data from the Ice Cloud and land Elevation Satellite from 2003-2004, ERS-1/2 radar altimeter data from 1994 corrected for temporal changes in between 1,14 and the new GGM02 geoid 15 . Comparison of the DEM with independent laser altimeter data at the grounding line of West Antarctica indicates a vertical precision in elevation of 0.15 ± 4 m. Surface elevation above mean sea level is then converted into solid-ice surface elevation after applying a firn depth correction 16 . We estimate the random error in inferred thickness to range from 80 to 120 m when accounting for uncertainties in grounding-line position, surface elevation, firn depth correction and geoid height.…”

Is Antarctica melting?

“…Ice thickness, if not measured directly from airborne radio echo sounding, is deduced from surface elevation of floating ice measured by satellite altimeters 27. In addition, regional atmospheric climate models have provided corrections for firn depth,28 and grounding line positions have been mapped with unprecedented accuracy using satellite radar interferometry. Ice thickness is known within 10 m with radio echo sounding and 80 m from hydrostatic equilibrium.…”