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High-Stakes Oceanography at Antarctica’s Dangerously Thinning Glacier

The collapse of Thwaites Glacier would unleash catastrophic sea level rise. Erin Pettit, one of more than 100 scientists involved with a new international collaboration, discusses how better ocean data will help predict the glacier’s – and humanity’s – fate.

Written by Jessica Leber Published on Read time Approx. 6 minutes
RRS James Clark Ross is one of the research ships that will be deployed in the international collaboration to study Thwaites Glacier.Credit British Antarctic Survey

Whether coastlines around the world remain habitable for the next few centuries may come down to the fate of a Florida-sized glacier that is remote and inhospitable even by Antarctica’s standards.

An urgent five-year, $25 million scientific campaign – the largest collaboration between the United States and United Kingdom in Antarctica since the 1940s – announced Monday aims to improve predictions of whether West Antarctica’s Thwaites Glacier will collapse and, if so, how quickly.

It is already thinning – melting rates have doubled since the 1990s, according to the National Science Foundation – but what is unknown is whether the glacier will become irreversibly unstable or if increasing snowfall might slow down its flow into the Amundsen Sea.

Oceans Deeply spoke with Erin Pettit, an associate professor of geophysics at the University of Alaska Fairbanks and co-leader of one of the collaboration’s eight research projects. With the help of tagged seals, long-range autonomous underwater vehicles (AUVs) and other advanced instrumentation, the Thwaites-Amundsen Regional Survey and Network (TARSAN) will gather key ocean data to help determine how quickly the glacier could melt from below.

Copyright NERC, Ben Gilliland

Pettit explained how a better understanding of ocean circulation in the area will play a major role in answering questions about the glacier that could significantly speed global sea level rise.

Oceans Deeply: The major question seems to be whether this destabilization of the Thwaites glacier will occur. Is that right?

Erin Pettit: That’s the big question. It’s one of the goals of this project, to understand it. We’re talking about it as a six-lane highway of ice coming out.

Many of the models suggest that it should be unstable, but it’s not quite yet or at least it doesn’t appear to be. It is retreating quickly now, but how quickly and whether it’s fully going to go unstable – or whether there will stabilizing factors that come in – is something we don’t yet know.

That is one of the goals of this project: to understand the potential for stabilizing factors, and if not, how quickly is it all going to disappear.

Oceans Deeply: What is known about the ocean’s role in these questions?

Pettit: Off the continental slope in the deep ocean, there’s the Circumpolar Deep Water, which is a relatively warm mass of water. Normally, that water stays deep in the ocean, and it would not come up onto the continental shelf and affect the ice.

I just saw today some data from our marine geologists. Some of their ocean coring suggests that [the circumpolar deep water] hasn’t been coming up onto the continental shelf for the last 8,000 years. They do have evidence of it coming up some 8,000 years ago: There was some warm water on the shelf. But since then until the mid-20th century, at least the cores that they drilled showed there wasn’t detectable [warmer] water on the shelf. Once this warm water gets up on the shelf, then it can work its way up these submarine troughs to the underside of the big ice shelves right up to the grounding line.

What’s been happening for the last 50 years or so is that the Antarctic circumpolar winds have been increasing, and those winds have been creating currents in the water that are driving circulation to pull that warm water from the edge of the continental slope right up to where it’s touching the glacier.

That’s the general process of what is known. Now that the water is up on the shelf, the variability or the intensity of the winds at the surface help control how much of that water can get underneath the glacier.

What we’re trying to do is to say, first of all: What do we know about the details of that connection between the atmospheric winds and the currents that are bringing this warm water in closer? Then, as that water gets closer to the glacier, the specific geometry of the glacial cavity will control how much of the heat from the water can actually be transferred into melting the ice.

We know the big picture idea of what is happening, and we’ve seen it in action from satellite imagery. But the kind of smaller scale details that really control the specific amounts of melting that come from certain amount of heat movement from the water are the gaps of understanding we’re trying to fill in.

Oceans Deeply: So it’ll depend on how the ocean circulation is changing in a very detailed way, in this one area.

Pettit: We know that this is happening in general, but we really want to figure out, well, how fast is all this going to happen? What is the real potential for the Thwaites Glacier to collapse? Then you have to start getting into the details.

One of the things that the TARSAN project is doing is to compare the Thwaites system to the Dotson, which is nearby. We want to use that comparison in order to tease out the most important parameters in terms of the ocean bathymetry and the geometry of the ice shelf itself.

Oceans Deeply: Is this kind of work pretty unprecedented or has it just never been done in this area?

Pettit: It’s a little bit of both. Slowly, over the last decade or two, we’ve been getting more and more ocean observations near these ice shelf fronts. There’s been a few excursions using autonomous vehicles underneath, such as underneath the Pine Island ice shelf.

The Thwaites Glacier in West Antarctica. (Credit Jeremy Harbeck)

We are both connecting a pretty wide, pretty broad set of oceanographic observations both under the ice shelf and near the ice shelf and through time – connecting that with the observations happening directly in the ice and in the atmosphere above the ice.

We are trying to get all of these measurements in a very coordinated fashion, so we can pull all of these ideas together. That, I think, is one of the things that is making the whole Thwaites initiative much more novel. The TARSAN project alone has eight scientists.

Oceans Deeply: How are you collecting all the data? I heard you’re turning to seals to help gather measurements.

Pettit: We are tagging seals and having a couple of AUVs involved that will go under the ice shelves, and then we’ll also have gliders that will be doing zigzags up and down in front of the ice shelves to collect those boundary data. Plus, all the stuff we do off the ships normally.

There have been ships out there [in the past] taking measurements. We are actually going to integrate all the moorings that have been left in that area. We’re going to integrate all of the [data] that other ships in the past have produced.

This also includes us deploying ocean instrumentation through a hole in the ice shelf. We’ll be measuring salinity and temperature and currents underneath the ice shelf through instruments deployed through the hole. Being able to link [this data] all together is what’s powerful.

Oceans Deeply: What is the role of climate change in these changes to the ocean circulation around Thwaites?

Pettit: A lot of it seems to have to do with these enhanced winds. The circumpolar winds have been increasing over the last 50-plus years. There are multiple but subtle changes in the ocean and atmosphere down there. Even subtle changes in the ocean currents and their connections to the atmospheric winds can drive that circumpolar deep water up onto the shelf.

Oceans Deeply: Will this research help understand melting along other ice shelves of Antarctica?

Pettit: What we learn about this system will actually help us understand the potential for changes in a lot of other systems. The nice thing about this system is that since it is changing quickly we can actually see these changes happening within our data sets and on these shorter timescales.

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