Mass Balance of Antarctic Ice Sheet 1992 to 2008 from ERS and ICESat:

    Gains Exceed Losses

--- Jay Zwally, NASA Goddard, USA


During 2003-2008, the mass gain of the Antarctic ice sheet from snow accumulation exceeded the loss from ice discharge by 43 ± 16 Gt /yr (2.3% of input), as derived from ICESat laser altimetry. The 101 Gt/yr gain in East Antarctica (EA) and the 68 G /yr gain in four drainage systems (DS) of West Antarctic (WA2) exceeded combined losses of 98 Gt /yr from three coastal DS of West Antarctic (WA1) and 28 Gt /yr from the Antarctic Peninsula (AP). Reanalysis of ERS radar-altimeter data, including a new post-glacial-rebound correction, indicates an even larger gain of 120 ± 50 Gt /yr during 1992-2001. In WA2 and EA, persistent dynamic thickening (excess of long-term accumulation over ice flux) contributed more than 170 Gt /yr to the net positive balance in both periods. Consistent with observed outlet-glacier accelerations, a loss increase of 66 Gt /yr in WA1 and AP from dynamic thinning dominated a gain increase of 9 Gt /yr from positive accumulation anomalies, accounting for most of the 77 Gt /yr decrease in the overall gain in the later period. During both periods, regional changes driven by short-term accumulation variations are small compared to dynamic changes. Although recent increases in dynamic thinning in WA1 and AP have been partially offset by accumulation increases, continuation at similar rates would initiate small Antarctic contributions to sea-level rise within a decade.