External influences on the Mertz Glacier Tongue (East Antarctica) in the decade leading up to its calving in 2010

The Mertz Glacier Tongue (MGT) in East Antarctica lost ~55% of its floating length in February 2010, when it calved large tabular iceberg C28 (78×35km). We analyze the behavior of the MGT over the preceding 12years using a variety of satellite data (synthetic aperture radar and Landsat imagery and Ice, Cloud, and land Elevation Satellite laser altimetry). Contact of its northwestern tip with the eastern flank of shoals from 2002/2003 caused eastward deflection of the ice flow by up to ~47°. This change contributed to opening of a major rift system ~80km to the south, along which iceberg C28 eventually calved. Paradoxically, the seabed contact may have also held the glacier tongue in place to delay calving by ~8years. Our study also reveals the effects of other, more localized external influences on the MGT prior to calving. These include an abrupt sideways displacement of the glacier tongue front by at least ~145m following an apparent collision with iceberg C08 in early 2002 and calving of numerous small icebergs from the advancing northwestern front due to the "chiseling" action of small grounded icebergs and seabed contact, resulting in the loss of ~36km2 of ice from 2001 to 2006. The example of the MGT confirms the need for accurate bathymetry in the vicinity of ice shelves and glacier tongues and suggests that the cumulative effect of external factors might be critical to understanding and modeling calving events and ice shelf stability, necessarily on a case-specific basis.