More Trouble at Totten Glacier

Last spring I interviewed Jamin Greenbaum of the University of Texas, a key researcher on one of the planet’s most remote areas, the vast expanses of East Antarctica vulnerable to warming ocean water.  He helped me flesh out the reasons why East Antarctica, long thought to be stable and resistant to the rapid melting taking place in West Antarctica – has now become a focus for researchers worried about just how rapidly large chunks of ice and significant amounts of sea level might come off that area.

Chris Mooney reports in the Washington Post about a new study with good news, bad news, and fresh uncertainty.

Washington Post:

Earlier this year, we learned some worrisome climate news. Although Antarctic scientists have been most concerned about loss of ice in the western part of Antarctica, a study in Nature Geoscience suggested a vulnerability in the much larger ice sheet of East Antarctica, as well.

East Antarctica’s enormous Totten Glacier, you see, has a key similarity with the glaciers of West Antarctica — namely, it is rooted deep below sea level. This means that it is potentially exposed to warm ocean waters, and the study in March uncovered a deep and 5-kilometer wide subsea valley beneath the glacier’s oceanfront ice shelf that, the authors said, could be a route for warm offshore water to reach its base. This might explain why the glacier has been observed to be thinning and lowering, or losing elevation, over time, they noted.

Located along East Antarctica’s Sabrina Coast, Totten glacier is the ice sheet’s largest. It holds back 3.9 meters of potential sea level rise, or over 12 feet, and connects with the very deep and vast Aurora Subglacial Basin, which is also rooted well below sea level. So the results were treated as being of enormous consequence.

But they’re not the end of the story, as there is vastly more to learn about Totten glacier. A new study out in Geophysical Research Letters reaffirms some of these core concerns about Totten’s melt — while also appearing to partly alleviate others.

Xin Li, a researcher at the University of California, Irvine, worked with a team from her institution and NASA’s Jet Propulsion Laboratory to examine Totten using satellite imagery and aircraft data. The researchers documented for the first time just how much the glacier’s “grounding line” — the critical underwater area where ice, bedrock and the ocean meet — has been retreating inland over the years.

The answer is quite a bit. The research found that between 1996 and 2013 Totten’s grounding line retreated as much as 3 kilometers in some places. That’s fast, but it’s not nearly so fast as what has been happening in West Antarctica, where the retreat in some areas has been as much as one to two kilometers per year.

“This boundary is very important because that’s where the ice detaches from the bed and becomes afloat and frictionless,” says Li of the grounding line. So any change here is not good news. The researchers were only able to get data for 20 percent of the vast Totten glacier’s grounding line, but this region accounted for 70 percent of the glacier’s current ice loss into the ocean, and for its fastest thinning.

A key question thus becomes whether the grounding line in this area could speed up its retreat and in particular, whether a “marine ice sheet instability,” which is thought to exist in West Antarctica, might also exist here. Such an instability is caused by the presence of a “retrograde” or downward-sloping seabed beneath the glacier, which means that warm water can continually get beneath the ice sheet as the grounding line retreats further and further downhill.

The answer, the new study suggests, is no. “Immediately upstream of the grounding line there is a 7 kilometer long region — we call it an ice plain because the slopes are really flat, and for this part of the glacier, it could retreat very fast, in a couple of decades or so,” says Li. After that, though, the elevation actually rises for 40 kilometers, and so the retreat would not happen as quickly.

“The bedrock topography at the end of the present Totten fjord (beneath the floating thick ice at the glacier front) is such that retreat is likely to proceed rapidly but then slow down,” observes Ted Scambos, lead scientist at the National Snow and Ice Data Center, who reviewed the new study for the Post. “There will be a glacier acceleration and thinning associated with the first retreat into a deep area but then some slowing.”

“This is an area harder to destabilize dramatically than in Thwaites area” of West Antarctica, adds Penn State University glaciologist Richard Alley, commenting on the new study. But, he continues, “warming waters can influence this area and access a lot of ice leading to long-term large sea-level rise.”

The new study, however, was not able to confirm or refute the existence of the canyon from the earlier paper in Nature Geoscience. There was no data available for the relevant area on the eastern side of the glacier — so this remains a possible route for how warm water may be reaching the glacier’s grounding line.
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Finally, they point to recent research suggesting new mechanisms that can destabilize truly gigantic and mostly submerged glaciers, like Totten, which are rooted well over 1,000 meters below sea level but also have ice extending over 100 meters into the air above sea level. If these glaciers lose their stabilizing ice shelves, the research suggests, then “ice cliff failure” will occur whenever there is a sheer ice face more than 100 meters high above the sea level.

Therefore, these researchers say they are still looking at Totten glacier as a potential key to solving one of the most important mysteries in climate research: In past eras of Earth’s history that weren’t all that much warmer than today, scientists believe seas were much, much higher – so much so that not even a collapse of West Antarctica, alone, could account for it. Thus, they’re busy looking for the missing ice – or, the missing ocean water – that will balance these past sea level budgets. And they think Totten and the Aurora basin could be the place that it came from.