Antarctic ice loss could warp Earth’s gravity field

The Antarctic has suffered a sudden massive increase in ice loss – equivalent of the volume of nearly 350,000 Empire State Buildings combined – in a previously stable region, scientists have revealed.

A research ship on the Filchner Ronne Ice Shelf in West Antarctica, which is rapidly melting. Picture: SWNS

The ice loss, reported in the journal Science, is so large that it causes small changes in the gravity field of the Earth.

Using measurements of the elevation of the Antarctic ice sheet made by satellites, researchers found that the Southern Antarctic Peninsula showed no signs of change up until 2009.

However, around 2009, multiple glaciers along a vast coastal expanse around 460 miles long suddenly started to shed ice into the ocean at a nearly constant rate of 60 cubic km, or about 55 trillion litres of water, each year.

The ice loss makes the region the second largest contributor to sea level rise in Antarctica and researchers say it shows no sign of waning.

Study leader Dr Bert Wouters, of Bristol University, said: “To date, the glaciers have added roughly 300 cubic km of water to the ocean. That’s the equivalent of the volume of nearly 350,000 Empire State Buildings 
combined.”

The changes were observed using a satellite called CryoSat-2, a mission of the European Space Agency dedicated to the remote-sensing of ice. From an altitude of around 700km, the satellite sends a radar pulse to Earth, which is reflected by the ice and subsequently received back at the satellite.

From the time the pulse takes to travel, the elevation of the ice surface can be gauged accurately. By analysing roughly five years of the data, the researchers found the ice surface of some of the glaciers is currently being cut by as much as four metres each year.

Dr Wouters said: “The fact that so many glaciers in such a large region suddenly started to lose ice came as a surprise to us.

“It shows a very fast response of the ice sheet: in just a few years, the dynamic regime completely shifted.”

Figures from an Antarctic climate model show that the sudden change cannot be explained by changes in snowfall or air temperature. Instead, the team attributes the rapid ice loss to warming oceans.

Many of the glaciers feed into ice shelves that float on the surface of the ocean. They act as a buttress to the ice resting inland, slowing down the flow of the glaciers into the ocean.

Westerly winds have become stronger in recent decades as a result of climate change and ozone depletion, and have pushed warm waters from the Southern Ocean towards the pole, eating away at the glaciers and floating ice shelves from below.

Ice shelves in the region have lost almost a fifth of their thickness in the past two decades, thereby reducing the resisting force on the glaciers. Much of the ice of the Southern Antarctic Peninsula is grounded on bedrock below sea level, which gets deeper inland. This means that even if the glaciers retreat, the warm water will chase them inland and melt them even more.

Dr Wouters added: “Compared to other regions in Antarctica, the Southern Peninsula is rather understudied, exactly because it did not show any changes in the past, ironically.

“To pinpoint the cause of the changes, more data needs to be collected. A detailed knowledge of the geometry of the local ice shelves, the ocean floor topography, ice sheet thickness and glacier flow speeds are crucial to tell how much longer the thinning will continue.”