Ocean Currents Speeding Melting Glaciers

New research has shown that strong ocean currents running under the West Antrarctic’s Pine Island Glacier Ice Shelf are eating away at the ice from below, contributing to the rapid decline in the shelf’s mass, thus increasing the amount of meltwater running into the oceans.

The new study, which appears in the journal Nature Geoscience, shows that over the last few decades, the Pine Island Glacier Ice Shelf has detached from an underwater ridge which has allowed more of the glacier to interact with deeper, and subsequently warmer, currents.

The glacier is believed to have detached sometime prior to the 1970s, and since then, warmer water has been eating away at more and more of the glacier as it slides into the water. As a result, a growing cavity beneath the ice shelf has formed, which itself allows more warm water to melt the ice, creating a feedback loop of melting and water run off which starts the process again.

According to estimates, the Pine Island Glacier Ice Shelf is currently sliding into the sea at a rate of four kilometres per year, and melting at about 80 cubic kilometres per year; that’s 50 percent faster than it was melting in the early 1990s.

“More warm water from the deep ocean is entering the cavity beneath the ice shelf, and it is warmest where the ice is thickest,” said study’s lead author, Stan Jacobs, an oceanographer at Columbia University’s Lamont-Doherty Earth Observatory.

This effect is being seen in other locations around the Amundsen Sea, including Thwaites Glacier and the much larger Getz Ice Shelf.

Possibly contributing to this deterioration is the evidence that Antarctica is actually getting windier as the years pass by, which in turn could explain the changes in ocean circulation allowing warmer waters access to parts of the icy continent never seen before. Stronger circumpolar winds would tend to push sea ice and surface water north, says Jacobs. That in turn, would allow more warm water from the deep ocean to upwell onto the Amundsen Sea’s continental shelf and into its ice shelf cavities.

While research and science like this may seem far away for many readers, especially those in the Northern Hemisphere, Pine Island Glacier Ice Shelf is being watched so closely because of the potential it has to affect sea level across the entire face of the planet.

Current estimates place global sea level rise at approximately 3 millimetres per year. But one estimate of the total collapse of the Pine Island Glacier Ice Shelf and its tributaries puts the global sea level rise as a direct result at 24 centimetres.

The paper adds important and timely insights about oceanic changes in the region, says Eric Rignot, a professor at University of California at Irvine and a senior research scientist at NASA’s Jet Propulsion Laboratory. “The main reason the glaciers are thinning in this region, we think, is the presence of warm waters,” he said. “Warm waters did not get there because the ocean warmed up, but because of subtle changes in ocean circulation. Ocean circulation is key. This study reinforces this concept.”

Source: The Earth Institute at Columbia University
Image Source: Maria Stenzel, at The Earth Institute

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