Antarctic Peninsula: Sudden Ice Loss Affects Earth's Gravity Field

While it's no secret that much of the Antarctic Peninsula is rapidly melting, scientists were disappointed when they recently found that a previously stable region of Antarctica is experiencing rapid ice loss - so much so that it is even affecting Earth's gravity field.

The Southern Antarctic Peninsula was believed to be one of the few areas left that was relatively unaffected by climate change. That is, until 2009 when multiple glaciers along a vast coastal expanse, measuring some 750 km (466 miles) in length, suddenly started to shed ice into the ocean at a nearly constant rate of 60 cubic km - or about 55 trillion liters of water - each year.

That's at least according to a new study published in the journal Science, which says that this sudden onset of ice loss now makes the region the second largest contributor to sea level rise in Antarctica. What's more, the flow rate shows no signs of waning anytime soon.

"To date, the glaciers 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," lead researcher Dr. Bert Wouters, a Marie Curie Fellow at the University of Bristol, UK, said in a statement.

The changes were observed using the CryoSat-2 satellite, a mission of the European Space Agency dedicated to remote-sensing of ice. About 5 years worth of data showed that the ice surface of some of the glaciers is currently decreasing by as much as 4 meters (13 feet) per year. This ice loss is so dramatic that it is enough to cause small changes in the gravity field of the Earth, which can be detected by another satellite mission, the Gravity Recovery and Climate Experiment (GRACE).

"The fact that so many glaciers in such a large region suddenly started to lose ice came as a surprise to us," Wouters said. "It shows a very fast response of the ice sheet: in just a few years the dynamic regime completely shifted."

So what exactly brought on this sudden ice loss?

Data from an Antarctic climate model rules out changes in snowfall or air temperature. Thus, the researchers believe it's actually because of warming oceans (summer 2014 saw the warmest ocean temperatures ever recorded).

Many of the glaciers in the region feed into ice shelves that float on the surface of the ocean. They support ice resting on bedrock inland, slowing down the flow of the glaciers into the ocean. However, climate change and ozone depletion have strengthened the westerly winds that encircle Antarctica. These stronger winds push warm waters from the Southern Ocean towards the Earth's pole, where they eat away at the glaciers and floating ice shelves from below.

Consequently, ice shelves in the region have lost almost one-fifth of their thickness in the last two decades, thereby reducing the resisting force on the glaciers.

Scientists are most concerned with the fact that 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.

"It appears that sometime around 2009, the ice shelf thinning and the subsurface melting of the glaciers passed a critical threshold which triggered the sudden ice loss," Wouters added. "However, 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 need to be collected," he said. "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."

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