Antarctic ice sheets show more cause for concern

A study assessing the 40 years of satellite imagery collected from the critical portion of the West Antarctic is showing signs of stress. The point where the vast ice sheets hold their grip onto the Antarctic continent is failing, and this could lead to a break up of the sheet in the Eastern Amundsen Sea.

The loss of the ice shelves do not constitute a net sea level rise, due to their already being in the ocean. The sheets act as a wall however, preventing grounded ice on the main Antarctic continent from sliding into the water; once these barriers are lost, the grounded ice upstream is likely to move faster and cause sea level rise.

The study was conducted by The University of Texas at Austin’s Institute for Geophysics, and led by Joseph MacGregor. He says, “Typically, the leading edge of an ice shelf moves forward steadily over time, retreating episodically when an iceberg calves off, but that is not what happened along the shear margins”. Instead the margins are heavily rifted and the calving front is retreating along the margins.

"As a glacier goes afloat, becoming an ice shelf, its flow is resisted partly by the margins, which are the bay walls or the seams where two glaciers merge," explains co-author Ginny Catania. "An accelerating glacier can tear away from its margins, creating rifts that negate the margins' resistance to ice flow and causing additional acceleration."

They also found that the largest accelerations of the glacier were happening upstream of the rifting margins, and the rifting is thought to be a result of the accelerations. It all adds up to a worrying situation.

The West Antarctic Ice Sheet is particularly unstable, because of the sea bed it sits upon. A small break up of the ice sheet could potentially destabilise the entire region with huge consequences for the ice on the mainland of the Antarctic continent. The climate of the Antarctic is also unusual, in that the central region is currently showing no sign of warming, whilst the outer reaches of the continent are undergoing significant warming. Modelling of the region is difficult too and as such, just how and when the ice sheet break up will occur, and how this will affect the central region, is unclear.