This is a dispatch from Constantino Panagopulos, a science writer at the Jackson School of Geosciences, who is documenting the TERMINUS mission to explore Greenland glaciers from underwater. The mission is led by Professor Ginny Catania and collaborators. Learn more about it here.
Greenland’s sea-facing glaciers are in constant motion. They’re the outlets through which the ice cap drains. Each year these glaciers shed about 100 billion tons of ice into the sea as icebergs, which calve from the glacier, often with much drama and a lot of ice debris.
It’s what makes glacial fjords so treacherous. Last Friday, for the scientists of TERMINUS, a research expedition in West Greenland led by The University of Texas at Austin, it very nearly spelled disaster.
The science deck was abuzz with activity. After waiting for the drone team to finish their aerial sweep, the expedition’s robot submersible, Nereid Under Ice (NUI), was finally in the water. I watched as the plucky submersible spun up its thrusters, ready to dive down to the glacier’s southern edge a mile and a half away.
Chief scientist Ginny Catania, a professor at UT Jackson School of Geosciences, was outside the bridge watching the drone reconnaissance surveys. The glacier, she said, had been rumbling all morning like an angry volcano. Then, at 2:19pm it let loose a giant iceberg.
Second officer Paddy Kenny was on the bridge when he heard Catania tapping on the window and pointing at the glacier.
“We looked round and saw what looked like the whole front of it collapsing,” he said. “Big lumps of it started breaking off, other bits started coming up from under the water. There was lots of movement, lots of ice, it sounded like thunder and lighting. But at the same time, it looked like it was happening in slow motion. It was quite the thing to see something that size moving and tumbling.”
Kenny and NUI’s expedition leader Molly Curran made the decision to pull NUI from the water.
With NUI back on deck, the TERMINUS team launched a drone to examine the carnage from above. The birds eye video showed that a section of ice 16 acres across had sheared from the glacier, split in two and spilled icy white debris across the fjord. The two icebergs had settled on their sides, exposing hundreds of meters of glacial layers, from their snowy tops to their dark, glassy base.
The deep blue color of the ice left an impression on the second officer.
“It’s the same turquoise as the eyes of those White Walkers from Game of Thrones,” Kenny said.
Back in science operations, Catania, Curran and the other TERMINUS scientists had pivoted the day’s science plan. Curran’s team would reconfigure NUI for a dive to another part of the glacier the following day. Meanwhile, the other scientists would use the day to fill in gaps in their surveys of the fjord’s seafloor and ocean.
In the field, the science never stops. And for Catania, the event was a chance to match what NUI’s underwater surveys had seen with the evidence now bobbing around on the fjord’s surface.
Previous NUI dives had revealed rows of submerged ice caves along much of the glacier’s face. Large holes in the ice face had been hypothesized before but they weren’t expected to be so numerous.
“My guess is that surface crevasses are bringing water down and eroding out this area (the ice caves) that then creates a weakness that allows calving to happen,” she said.
Undermining the ice from below is one of several ways to split icebergs from glaciers. Other ways include fractures, faults and meltwater channels carving indentations in the ice. Scientists don’t yet know which of these processes is most influential overall, but the data the TERMINUS project is capturing from both underwater and above could help them reach a consensus.
Ice caves and icebergs are just part of the picture, revealed in detail by NUI, of how glaciers lose their ice at the ocean. The submersible also found sheer, cliff-like surfaces hundreds of meters tall.
According to the expedition’s oceanographer, Bridget Ovall, these were likely shaped by meltwater spraying out from under the glacier and rolling up the face in eddies, like smoke from a chimney stack, wearing the ice down to a flat surface as it mixed with warmer ocean water.
With the fjord now glassy-still again, the Celtic Explorer gently nudged aside bits of icy flotsam as it passed slowly back and forth across the fjord. A distant rumble rolled down the valley from somewhere unseen. In the environment of the glacial fjord, the ice bergs arrival had been a dramatic reminder that though the landscape maybe frozen, it’s never still.
This is the sixth dispatch on the mission. To see the rest, visit the TERMINUS mission blog.