Melting of ice shelves and the mass balance of Antarctica

Abstract

We calculate the present ice budget for Antarctica from measurements of accumulation minus iceberg calving, run-off and in situ melting beneath the floating ice shelves. The resulting negative mass balance of 469 Gt year−1differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20–50%. Annual accumulation from an earlier review is adjusted to include the Antarctic Peninsula for a total of 2144 Gt year−1. An iceberg production rate of 2016 Gt year−1is obtained from the volume of large icebergs calculated from satellite images since 1978, and from the results of an international iceberg census project. Ice-shelf melting of 544 Gt year−1is derived from physical and geochemical observations of meltwater outflow, glaciological field studies and modeling of the sub-ice ocean circulation. The highest melt rates occur near ice fronts and deep within sub-ice cavities. Run-off from the ice-sheet surface and from beneath the grounded ice is taken to be 53 Gt year−1. Less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0.45 mm year−1in the IPCC “best estimate” of the recent global sea-level rise.

Evaluating the Hydrological Cycle over Land Using the Newly-Corrected Precipitation Climatology from the Global Precipitation Climatology Centre (GPCC)

“…Since the WaterGap 2.2 model does not include glacier dynamics, we added 280 km 3 per year attributed to iceberg calving in Greenland [31] to the GRDC estimate. Together with a runoff estimate for Antarctica of 2613 km 3 per year [32] this resulted in a total surface runoff of about 44,800 km 3 per year. Lacking other quantitative information for the annual groundwater flow into the oceans we assumed this quantity to be on the order of 1000 km 3 , and arrived at a total runoff (rivers and groundwater) of about 45,800 km 3 per year, close to the recent estimate for the global runoff of 45,900 km 3 per year [14].…”

Explicit representation and parametrised impacts of under ice shelf seas in the <i>z</i><sup>∗</sup> coordinate ocean model NEMO 3.6

“…The process is referred to as an ice pump when the ascending waters cause refreezing (Lewis and Perkin, 1986). Jacobs et al (1992) identified three modes of overturning, depending on the inflowing water mass, which could be either high-salinity shelf water (HSSW; mode 1), modified forms of Circumpolar Deep Water (CDW; mode 2) or less saline water masses that could collectively be referred to as Antarctic Surface Water (AASW; mode 3). Mode 1 melt is low, because HSSW has a temperature close to the surface freezing point and can melt ice at depth only because of the lowering of its freezing point with increasing pressure.…”

Inputs of glacially derived dissolved and colloidal iron to the coastal ocean and implications for primary productivity

“…The major mass loss from the Antarctic Ice Sheet is ice berg calving [Church et al, 2001]. By contrast, the flux of direct glacial runoff from Antarctica is not well known [Dierssen et al, 2002], but is believed to be smaller, and in the range of $0.04-5 Â 10 10 m 3 /a [Jacobs et al, 1992]. Recent work indicates the presence of abundant and dynamic subglacial water beneath both West [Fricker et al, 2007;Gray et al, 2005] and East [Siegert et al, 2005;Wingham et al, 2006] Antarctica.…”

“…Recent work indicates the presence of abundant and dynamic subglacial water beneath both West [Fricker et al, 2007;Gray et al, 2005] and East [Siegert et al, 2005;Wingham et al, 2006] Antarctica. Fricker et al [2007] demonstrate $0.7 Â 10 9 m 3 /a of subglacial water draining from beneath one (Whillans) of the West Antarctic Ice Streams, suggesting that the upper estimate of Jacobs et al [1992] may be more representative for the entire continent. However, the direct runoff may leave a significant imprint on the surrounding coastal waters.…”