Fernando S. Paolo

Volume loss from Antarctic ice shelves is accelerating

Disappearing faster around the edges The floating ice shelves around Antarctica, which buttress ice streams from the continent and slow their discharge into the sea, are thinning at faster rates. Paolo et al. present satellite data showing that ice shelves in many regions around the edge of the continent are losing mass. This result increases concern about how fast sea level might rise as climate continues to warm. If warming continues to cause ice shelves to thin, as they have for the past couple of decades, their disappearance may allow land-based ice to collapse and melt. Science, this issue p. 327 Ice shelves around much of Antarctica have been thinning over the past two decades. The floating ice shelves surrounding the Antarctic Ice Sheet restrain the grounded ice-sheet flow. Thinning of an ice shelf reduces this effect, leading to an increase in ice discharge to the ocean. Using 18 years of continuous satellite radar altimeter observations, we have computed decadal-scale changes in ice-shelf thickness around the Antarctic continent. Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 cubic kilometers per year for 1994–2003 to rapid loss of 310 ± 74 cubic kilometers per year for 2003–2012. West Antarctic losses increased by ~70% in the past decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades.

Ocean forced variability of Totten Glacier mass loss

Abstract A large volume of the East Antarctic Ice Sheet drains through the Totten Glacier (TG) and is thought to be a potential source of substantial global sea-level rise over the coming centuries. We show that the surface velocity and height of the floating part of the TG, which buttresses the grounded component, have varied substantially over two decades (1989–2011), with variations in surface height strongly anti-correlated with simulated basal melt rates (r = 0.70, p < 0.05). Coupled glacier–ice shelf simulations confirm that ice flow and thickness respond to both basal melting of the ice shelf and grounding on bed obstacles. We conclude the observed variability of the TG is primarily ocean-driven. Ocean warming in this region will lead to enhanced ice-sheet dynamism and loss of upstream grounded ice.

ICESAT/GLAS Altimetry Measurements: Received Signal Dynamic Range and Saturation Correction

NASA’s Ice, Cloud, and land Elevation Satellite (ICESat), which operated between 2003 and 2009, made the first satellite-based global lidar measurement of earth’s ice sheet elevations, sea-ice thickness, and vegetation canopy structure. The primary instrument on ICESat was the Geoscience Laser Altimeter System (GLAS), which measured the distance from the spacecraft to the earth’s surface via the roundtrip travel time of individual laser pulses. GLAS utilized pulsed lasers and a direct detection receiver consisting of a silicon avalanche photodiode and a waveform digitizer. Early in the mission, the peak power of the received signal from snow and ice surfaces was found to span a wider dynamic range than anticipated, often exceeding the linear dynamic range of the GLAS 1064-nm detector assembly. The resulting saturation of the receiver distorted the recorded signal and resulted in range biases as large as ~50 cm for ice- and snow-covered surfaces. We developed a correction for this “saturation range bias” based on laboratory tests using a spare flight detector, and refined the correction by comparing GLAS elevation estimates with those derived from Global Positioning System surveys over the calibration site at the salar de Uyuni, Bolivia. Applying the saturation correction largely eliminated the range bias due to receiver saturation for affected ICESat measurements over Uyuni and significantly reduced the discrepancies at orbit crossovers located on flat regions of the Antarctic ice sheet.

Publisher Correction: Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation

In the version of this Article originally published, there was a spelling mistake in Figure 3 where ‘La Niña’ was incorrectly spelled ‘La Niño’. This has been corrected in all versions of the Article.