Articles | Volume 9, issue 3
The Cryosphere, 9, 1005–1024, 2015
The Cryosphere, 9, 1005–1024, 2015

Research article 13 May 2015

Research article | 13 May 2015

Oceanic and atmospheric forcing of Larsen C Ice-Shelf thinning

P. R. Holland1, A. Brisbourne1, H. F. J. Corr1, D. McGrath3,2, K. Purdon4, J. Paden4, H. A. Fricker5, F. S. Paolo5, and A. H. Fleming1 P. R. Holland et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2USGS Alaska Science Center, Anchorage, Alaska, USA
  • 3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
  • 4Center for Remote Sensing of Ice Sheets, University of Kansas, Lawrence, Kansas, USA
  • 5Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA

Abstract. The catastrophic collapses of Larsen A and B ice shelves on the eastern Antarctic Peninsula have caused their tributary glaciers to accelerate, contributing to sea-level rise and freshening the Antarctic Bottom Water formed nearby. The surface of Larsen C Ice Shelf (LCIS), the largest ice shelf on the peninsula, is lowering. This could be caused by unbalanced ocean melting (ice loss) or enhanced firn melting and compaction (englacial air loss). Using a novel method to analyse eight radar surveys, this study derives separate estimates of ice and air thickness changes during a 15-year period. The uncertainties are considerable, but the primary estimate is that the surveyed lowering (0.066 ± 0.017 m yr−1) is caused by both ice loss (0.28 ± 0.18 m yr−1) and firn-air loss (0.037 ± 0.026 m yr−1). The ice loss is much larger than the air loss, but both contribute approximately equally to the lowering because the ice is floating. The ice loss could be explained by high basal melting and/or ice divergence, and the air loss by low surface accumulation or high surface melting and/or compaction. The primary estimate therefore requires that at least two forcings caused the surveyed lowering. Mechanisms are discussed by which LCIS stability could be compromised in the future. The most rapid pathways to collapse are offered by the ungrounding of LCIS from Bawden Ice Rise or ice-front retreat past a "compressive arch" in strain rates. Recent evidence suggests that either mechanism could pose an imminent risk.

Short summary
Antarctic Peninsula ice shelves have collapsed in recent decades. The surface of Larsen C Ice Shelf is lowering, but the cause of this has not been understood. This study uses eight radar surveys to show that the lowering is caused by both ice loss and a loss of air from the ice shelf's snowpack. At least two different processes are causing the lowering. The stability of Larsen C may be at risk from an ungrounding of Bawden Ice Rise or ice-front retreat past a 'compressive arch' in strain rates.