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Southern Surveys: Unravelling the mystery of East Antarctica

by Dan Zlotnikov on April 13, 2015 applied

Jamin Greenbaum, a researcher at the University of Texas Institute for Geophysics, is the lead author of a new paper reporting on the discovery of two seafloor gateways that could allow warm ocean water to reach the base of Totten Glacier, East Antarctica’s largest and most rapidly thinning glacier.
Photo credit: Svetlana Burris

Oceanic gateways could explain rapid glacier thinning in East Antarctica

East Antarctic static and boring? Far from it, as a March, 2015 Nature Geoscience paper authored by Jamin Greenbaum and an international team of collaborators explains.

Warm ocean water has been observed since 1996 below 400 to 500m of cool surface water offshore of the Totten Glacier, the largest and most rapidly thinning glacier in East Antarctica. Until now, Totten Glacier was thought to be insulated from the warm, deep water by a shallow basement ridge making the cause of its high thinning rate a mystery possibly explained by grounded ice processes.  Using airborne gravity and magnetics, Greenbaum revealed two deep seafloor valleys that could allow the warm ocean water to reach the base of the glacier’s floating section and drive rapid melt. The discovery likely explains the glacier’s extreme thinning and raises concerns about how it will impact sea level rise. The result is of global importance because the ice flowing through Totten Glacier alone is sufficient to raise global sea level by at least 11 feet, equivalent to the contribution of the West Antarctic Ice Sheet if it were to completely collapse.

“We now know there are avenues for the warmest waters in East Antarctica to access the most sensitive areas of Totten Glacier,” said lead author Jamin Greenbaum, a UTIG Ph.D. candidate. “Knowing this will improve predictions of ice melt and the timing of future glacier retreat.”

A map showing the previously-hidden landscape beneath and seaward of Totten Glacier’s floating ice shelf. The orange arrows indicate seafloor gateways deep enough to allow warm water to enter beneath the floating ice. The solid orange arrow leads to the deeper of the two gateways, a three-mile-wide seafloor valley that connects to the coast in an area that was previously believed to be cut off from the ocean but that the team showed is actually floating (red lines). Topography landward of the grounding line (white) was assembled from ice sounding radar data. The interpretation was generated in Oasis montaj by Jamin Greenbaum

[Click to enlarge]

The Totten Glacier catchment (outlined in blue) is a collection area of ice and snow that flows through the glacier. It's estimated to contain enough material to raise sea levels by at least 11 feet. Image credit: Australian Antarctic Division

[Click to enlarge]

Oasis montaj GM-SYS 3D model setup and glacier input data for the gravity inversion used to produce the inferred seafloor: Vertical density distribution (left), ice bottom elevation (center), and ice surface elevation (right). Image credit: Jamin Greenbaum

Jamin Greenbaum came to data acquisition in a circuitous way. An aerospace engineer by training, he worked at NASA on satellites and on one of the early Mars rovers. The work was gratifying, but over time he came to realize his interests lay elsewhere.

“Working on hardware and designing instruments was interesting,” he concedes, “but I felt my calling was in the sciences, especially in areas requiring complex data acquisition and fieldwork.”

Greenbaum is currently a Ph.D. candidate and technical staff member in the airborne geophysics group at the University of Texas Institute for Geophysics (UTIG), in Austin. Led by Dr. Donald Blankenship, the group has been conducting airborne surveys all over Antarctica for more than two decades. Their work in East Antarctica has continued over the last seven years as a part of a large international collaboration between the US, UK, Australia, France, and Italy. The work is challenging, but vital because the East Antarctic Ice Sheet contains a large proportion of the Earth’s ice. If this ice melts faster than it is replenished by interior snowfall, global sea level will rise and the lives of hundreds of millions of people will be affected. The group’s primary motivation is understanding the processes governing ice sheet behavior as it relates to sea level potential.

An aerial photo of the Totten Glacier ice shelf. Photo credit: Jamin Greenbaum

The team’s BT-67 aircraft is outfitted with 450 kg of scientific equipment including radar that can measure ice several kilometers thick, lasers to measure the shape and elevation of the ice surface, and equipment that senses the earth’s gravity and magnetic field strengths, used to infer ice-covered geology. When Greenbaum joined the team, he was new to airborne surveys, and his academic fellowship didn’t have a lot of money for software. Then he learned about Geosoft, and discovered it had just what he needed to integrate and visualize the data. He called the company, described the project and was able to get up and running with the software (within his limited budget) as part of Geosoft’s education program.

Most of UTIG’s surveys are conducted from the air. But in February and March 2014, Greenbaum joined a shipborne expedition to East Antarctica’s Sabrina Coast, close to where he has been focusing his research using airborne data.

The expedition’s focus was the continental shelf near Totten Glacier, the most rapidly thinning glacier in East Antarctica. Totten is also significant because of its immense catchment found in the interior, a collection of ice and snow ¾ the size of Texas that drains to the coast through a single fjord 150km long and 30km across. Notes Greenbaum, “the ice is an unbelievable 2.5km deep where it starts to float.”

Totten Glacier’s interior catchment contains enough ice to raise global sea level by 3.5 metres – roughly the same as the potential of the entire West Antarctic Ice Sheet which drains through multiple glaciers. For many years, scientists believed East Antarctica was static and not a likely contributor to near term sea level change. The UTIG team has shown that warm water flowing 400-500m below the surface is likely accessing and rapidly melting the floating section of Totten Glacier, which could explain its rapid thinning.

The particular type of warm water near Totten Glacier is saltier (therefore denser), so it remains at depth, filling canyons in the seafloor. Seafloor valleys connecting this deep warm water to the coast can especially compromise glaciers, a process previously known to be occurring along the coast of the West Antarctic Ice Sheet. Greenbaum inverted airborne gravity data in Geosoft's GM-SYS Profile and GM-SYS 3D applications to identify the valleys.

 “The ship and airborne surveys wound up being very complementary,” he says. “We had previously flown where the ship was unable to sail, but the ship managed to intersect the airborne tracks in places which allowed some registration between the two datasets.”

The research team in Antarctica.
Photo Credit: Gregory Ng

The team’s efforts are already gaining recognition. Greenbaum is lead author on a paper published in the journal Nature Geoscience on March 16th that reveals the seafloor valleys deep enough to allow the warmest waters to enter beneath Totten Glacier’s floating section. The story has been picked up by several media outlets including the Washington Post and CNN in the US and The Telegraph in the UK with some articles already translated to Spanish and Swedish. Greenbaum welcomes the global attention, noting “sea level rise is a global problem and requires an international solution.”

A follow-up Australian marine expedition to the region which recently returned from the Totten Glacier area extended the data from last year’s cruise. UTIG’s airborne team will be back at work in November, continuing their airborne acquisition in the area.

With the datasets from the airborne and marine expeditions, UTIG and its international group of collaborators are well-positioned to continue expanding our understanding of this dynamic, important part of the world.

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