Cooperative Institute for Research in Environmental Sciences

Project Summary:

Significant glaciological and ecological changes are occurring along the Antarctic Peninsula in response to climate warming that is proceeding at 6 times the global average rate (King et al., 1994; Vaughn et al., 2003). Floating ice shelves, the extension of outlet glaciers, are responding rapidly and have lost ~28,000 km² in the last 50 years, including the catastrophic collapse of Larsen A in 1995, Larsen B in 2002 and the Wilkins ice shelf in 2008-09 (Cook and Vaughn, 2009). Following ice shelf collapse, the outlet glaciers that nourished the ice shelves have accelerated and thinned in response to the removal of the backstress that the ice shelf provided. In the case of Larsen B, an additional -27 km³ yr^-1 of ice was discharged due to the removal of this backstress (Rignot et al., 2004).

The significance of ice shelf collapse and subsequent acceleration of outlet glaciers is amplified by the fact that 40% of the Antarctic continent is ringed in ice shelves and that 80% of ice flux from the continent passes through these gates (Drewy, 1982; Jacobs et al., 1992). The climatic regime of the Antarctic Peninsula and the latitudinal changes in ice shelf stability provide a unique opportunity to study the full spectrum of ice shelf stability—from recently collapsed to fully stable—in order to gain a broader understanding of the climatic conditions and physical processes that result in ice shelf stability and instability. This understanding is essential to future estimates of ice sheet contributions to global sea level rise.

This project focuses on Larsen C, the largest remaining ice shelf on the Antarctic Peninsula. Larsen C has a surface area of ~55,000 km² and is composed of 12 major flow units fed by outlet glaciers (Glasser et al., 2009). Average ice thickness is ~300 m but ranges from ~500 m near the grounding line to ~250 m near the ice edge (Griggs and Bamber, 2009).

Field Activities:

Three automatic weather stations (AWS) were installed in 2008 along a north-south transect. Each AWS measures a total of 32 climatological and glaciological parameters, with a sampling rate of 10 s and the final storage of hourly mean values. The main parameters are temperature, humidity, wind speed and direction at two levels, both total and reflected shortwave radiation, net radiation, changes in surface height and pressure. Data is transmitted hourly using a GOES satellite link. Each station also contains a Trimble GPS receiver (R7 and NetRS) to measure ice shelf velocity.

During the 2009 field season, extensive ice penetrating radar and kinematic GPS surveys were conducted along and across flow lines near each AWS station. These surveys were aligned with current and future airborne missions (NASA/CECS and NASA ICE Bridge). The primary radar setup was a Mala GeoSciences 25 MHz rough terrain system that was towed behind a snowmobile. Numerous snowpits and shallow firn cores were taken to characterize annual accumulation, firn density and melt layer frequency.

References:

• Cook, A. J., D.G. Vaughan (2010). "Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years." The Cryosphere 4: 77-98.
• Drewry, D. J., S.R. Jordan, E. Jankowski (1982). "Measured properties of the Antarctic ice sheet: surface configuration, ice thickness, volume and bedrock characteristics." Annals of Glaciology. 3: 83-91.
  
• Glasser, N. F., B. Kulessa, et al. (2009). "Surface structure and stability of the Larsen C ice shelf, Antarctic Peninsula." Journal of Glaciology. 55: 400-410.
  
• Griggs, J. A., J.L. Bamber (2009). "Ice shelf thickness over Larsen C, Antarctica, derived from satellite altimetry." Geophysical Research Letters. 36.
  
• Jacobs, S. S., H. H. Helmer, et al. (1992). "Melting of ice shelves and the mass balance of Antarctica." Journal of Glaciology. 38: 375-387.
  
• King, J. C. (1994). "Recent climate variability in the vicinity of the Anarctic Peninsula." International Journal of Climatology 14: 357-369.
  
• Rignot, E., G. Casassa, et al. (2004). "Accelerated ice discharge from the Antarctic Peninsula following the collapse of Larsen B ice shelf." Geophysical Research Letters. 31.
  
• Vaughan, D. G., G.J. Marshall, W.M. Connolley, C. Parkinson, R. Mulvaney, D.A. Hodgson, J.C. King, C.J. Pudsey, J. Turner (2003). "Recent rapid regional climate warming on the Antarctic Peninsula." Climatic Change 60: 243-274.