Journey to Antarctica: Mapping Thwaites Glacier - Rolling Stone
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Journey to Antarctica: Mapping Thwaites

Why mapping the sea floor in front of this glacier is so important

Caption: Scientist Ali Graham on the bridge of the Nathaniel B. Palmer near Thwaites glacier in AntarcticaCredit: Jeff GoodellCaption: Scientist Ali Graham on the bridge of the Nathaniel B. Palmer near Thwaites glacier in AntarcticaCredit: Jeff Goodell

Scientist Ali Graham on the bridge of the Nathaniel B. Palmer near Thwaites glacier in Antarctica.

Jeff Goodell

This is the 10th dispatch in a series from Jeff Goodell, who will be investigating the effect of climate change on Thwaites glacier.

Ali Graham, a 37-year-old geophysicist from the U.K.’s University of Exeter, is a tall, thin man with a pointy beard and a soft-spoken manner. When he’s not at his desk in the forward dry lab on the Nathaniel B. Palmer, the icebreaker we’ve been aboard in Antarctica for the last month exploring the risk of collapse of Thwaites glacier, he’s likely out on the deck in an orange float coat working on a sediment core, or on the satellite phone, speaking in an adoring dad sorta way with his two-year-old daughter.

One of Graham’s jobs is to oversee the devices that scientists are using on this trip to map the sea floor in front of Thwaites glacier. For Graham, this means sitting in front of a monitor for hours each day, watching brightly-colored images of the sea floor appear on his screen, and discussing strategies with Kelly Hogan, a marine geophysicist with the British Antarctica Survey, about which areas need to be explored more deeply.

Last Saturday morning, Graham sat down with Aleksandra Mazur, a researcher at Sweden’s University of Gothenburg, to pore over data from the latest Hugin mission. The Hugin is an automated underwater device that’s equipped with a variety of instruments, including a multibeam echosounder, which uses sound waves to map the ocean floor. Multibeams are common tools on oceanographic research ships, but the multibeam on the Hugin takes the technology to a whole new level, allowing scientists to see individual rocks, fissures and iceberg tracks thousands of feet below the sea surface.

Mazur and Graham were scrolling through the Hugin data, glancing at the usual ridges and rocks and then … “Whoa!” Graham thought. He stopped scrolling and looked closer. There were marks on the sea floor, features that Graham had suspected might exist, but had never really seen clearly. But here they were, clear as day. It was one of those ‘holy shit’ moments that happen sometimes in science, and in life, when you see something that fundamentally rocks your world.

One of the central missions of this trip has been to map the sea floor in front of Thwaites. Why? Because Thwaites, like most glaciers in West Antarctica, isn’t melting the way an ice cube melts on a sidewalk on a hot summer day. Antarctica a very cold place — there is virtually no surface melting here. Instead, the heat that’s causing all the trouble in West Antarctica comes from the ocean — specifically, from the Circumpolar Deep Water which wells up out of the deep ocean around Antarctica, and paradoxically, is warmer than the surface waters which are chilled by glacial meltwater and the freezing polar temperatures. In recent decades, more and more of this warm water has been flowing up onto the continental shelf and under the glacier toward an area called the grounding line, where the ice meets the sea floor. To put it simply, Thwaites is melting from below, causing the glacier to become unstable and raising concern that it could collapse in a civilization-threatening way.

Until now, the entire bay in front of Thwaites, a roughly 400 square mile area, was completely uncharted. That was a big problem, because to understand why more warm water is flowing under Thwaites, scientists need to understand the terrain of the sea floor in front of the glacier. Are there deep channels that funnel warm currents toward the grounding line? Where exactly do those troughs begin and end? How deep are they? For climate modelers, all this is key to their ability to project just how big the risk is that Miami Beach will soon be scuba diving zone.

On the Palmer, the main tool for seabed mapping is the ship’s multibeam. The multibeam is basically a giant stereo speaker that has been built into the hull of the ship, which blasts down high frequency (12 kHz) sound pulses in a wide swath as the ship cruises along. A receiver, which is mounted on another part of the hull, listens to the echo of those pulses, feeding the data to a computer which calculates the time it takes to echo return. Then, after running through a lot of sophisticated algorithms to correct for the ship’s speed, pitch, and yaw, the computer creates a three-dimensional real-time image of the ocean floor as we are cruising over it. It’s spooky-cool to sit in the lab with Graham or Hogan and watch the swaths of color roll out — you can see undulations, trenches, other features, all in vivid colors (shades of deepening blue indicate depth, reds and yellows indicate shallow areas). It’s like looking through a microscope for the first time and realizing the world you see isn’t the only world that exists.

Caption: Images of the sea floor on multibeam echosounder aboard the Nathaniel B. Palmer in Antarctica Credit: Jeff Goodell

Images of the sea floor on multibeam echosounder aboard the Nathaniel B. Palmer in Antarctica. Photo credit: Jeff Goodell

Jeff Goodell

Multibeams were invented in the 1960s by the U.S. Navy to help with submarine navigation and are now used to scout offshore oil drilling sites and undersea cable routing. But ship-based multibeams have their limitations. On the Palmer, multibeam data can be blurred by rough seas, which causes bubbles under the hull that distort the data. In addition, you can only map where the ship can go — which means you have to detour around big icebergs (in Antarctica, some are the size of LAX). And you can’t get under ice shelves or near the glacier’s grounding line, which, for climate scientists, is where all the action is.

But most problematic of all, the resolution for multibeam is only about 70’ x 70’ blocks, which makes it fine for revealing general contours, but not much more. “With the ship’s multibeam, you couldn’t see a London bus if it were parked on the sea floor,” explains Graham.

But on this cruise, scientist have a secret weapon: the Hugin. For mapping, the Hugin is an awesome tool. It can go under ice shelfs and icebergs, investigating areas where no ship can venture. Its multibeam also operates at a much higher frequency than the device on the ship, allowing it to deliver images that are about 20 times higher resolution. Which means that, if there were a bus on the sea floor, the Hugin would not only see it, but it might be able to tell you how many people were in it.

Here’s a comparison of the sea floor in front of Thwaites as seen by the multibeam on the ship vs. the multibeam on the Hugin:

The downside of the Hugin is that it offers a much narrower image than the ship’s multibeam — it’s flashlight in the darkness, compared to the ship’s floodlight.

The Hugin mission that revealed the marks on the sea floor that wowed Graham was the first to venture under the ice shelves. It traveled nearly a half mile under 1,500 feet of ice, a remarkable accomplishment in itself. But, interestingly, the features they saw that were so striking were not under the ice, but out in what is now open water, beneath where the ice shelf used to be.

I’d like to tell you exactly what they saw, and why it is important. But for some strange reason, world-class scientists prefer to have their discoveries revealed in journals like Science and Nature instead of Rolling Stone, so I have promised not to reveal too much. But I can say that it you didn’t have to have a Ph.D to realize the features on the sea floor were unusual, distinctive, and, as Hogan says, “a signature of change.” To put it another way, perhaps they were not evidence that Thwaites is in full-scale collapse. But they were certainly not evidence of stability. And given the risk Thwaites poses to coastal cities around the world, that’s a BFD.

The ship buzzed with excitement as news of the discovery spread. A crowd gathered around the desk in the forward dry lab around Mazur’s computer screen. Graham and Hogan were joined by Anna Wåhlin, the lead scientist on the Hugin team, and Rob Larter, the chief scientist on this cruise. They debated the possible causes of what they were seeing, measured the size and scale of the markings, riffed about glacial retreat and ocean currents. Several scientists worried that they were seeing on the screen were artifacts — deformities in the images caused by flawed data. One scientist joked that the marks looked like something left behind by aliens. Another retorted that they looked like they had been made by the Russian military. To which Wåhlin, who is always quick with a wry comment, joked, “Maybe it was Russian aliens!”

Within 24 hours, the buzz died down as scientists on the ship tried to digest the news and moved on to other experiments, as well as the upcoming finale of the ship’s ping-pong tournament. But nobody who saw those remarkable markings on the sea floor yesterday (including myself) doubted that something important had been revealed about how our world works.

“You come to a place with some ideas about what you might find — and then you find something entirely different or unexpected,” Graham told me later, sitting up on the bridge of the ship, surrounded by icebergs the size of aircraft carriers. “So you have to throw out all your old assumptions and start thinking again. That’s how science works.”


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