TERMINUS Blog: The Science of Mud

August 21, 2024

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. This is the seventh dispatch on the mission. To see the rest, visit the TERMINUS mission blog.

It’s a cold, pale night on the deck of the research vessel Celtic Explorer. The deck crew guide a long, torpedo-like tube vertically over the side and into the near-freezing fjord below.

The crane unreels steadily for several minutes then stops. Hundreds of meters below, the gravity core slams into the seafloor sealing a perfect cylinder of mud into its six-meter-long steel body. The crane spins back to life and the core is hauled on deck.

With the precious seafloor cargo on board, the ship’s engines rumble to life and the vessel moves to its next site, the croak-croak of the seismic chirp announcing our passage across the fjord.

I’m with the night shift scientists of the TERMINUS expedition in Western Greenland. For the next eight hours we’ll travel back and forth over a submerged plateau facing the glacier Kangerlussuup Sermia, stopping at intervals to carve cores from the seafloor.

Mikayla Pascual, a graduate student at the Jackson School of Geosciences talks me through what happens after the cores are aboard.

Once on-deck, the core is cut into five-foot sections onto which Pascual etches a name and number on its plastic sleeve, identifying where it was gathered and when. The cores are then x-rayed and passed through a core logger — a machine with a small, built-in capsule of cesium that it uses to record the density and magnetic properties of the mud and sand inside the core. They’re then stacked and stored for transportation to onshore laboratories.

Back home in Austin, Texas, Pascual works with computer models that simulate the advance and retreat of icesheets. It’s a far cry from hauling muddy cores around a research vessel in subzero temperatures, but what’s inside the cores could be essential information for better understanding future sea level rise, she said.

“Greenland is a rapidly changing ice sheet, it’s losing ice and raising sea levels a lot faster than Antarctica,” she said. “And so to understand how much ice it’s losing by the end of the century will be really important for coastal communities all over the world, especially if it’s losing ice at a faster rate than we thought.”

The data Pascual needs for her models is an accurate sedimentation rate. In other words how much mud gets dumped into the fjord by the glacier, where it goes and what that might say about future sea level rise.

Seeing the mud and cores up close is especially important for students who spend most of their time working on computational models, Pascual said.

“It helps me put my models into perspective,” she said.

University of Florida Professor John Jaeger, who heads the TERMINUS expedition’s marine geology team told me that the cores are also an important record of the glacier’s advance and retreat over the last few hundred years.

“It’s interesting because it’s kind of tied in with Viking history,” he said. “Around 1,000AD we had the medieval warm period, which is when the Vikings colonized Southern Greenland because the glaciers had retreated. And then about 400 years later, the Northern Hemisphere goes into the Little Ice Age, the ice re-advanced and they all left.”

During that period of global cooling, the glacier built a large moraine in front of it, like a submerged sandbank, which the TERMINUS surveys suggest was formed by the mud spewing out from under the ice.

As glaciers slide downhill, they grind away at the bedrock turning it to a fine powder that turns to silky mud when mixed with water. Curiously, the finest sediment particles cluster together like snowflakes when they’re ejected into the fjord from under the ice, Jaeger said. The sediment torrent is so thick and strong near the ice it’s like being in an underwater blizzard, he said.

But nearest the ice is where the most valuable seafloor samples are to be found.

“It’s the mystery zone that we’ve never been able to get to with ships,” Jaeger said.

That’s where the expedition’s robot submersible, Nereid Under Ice (NUI) comes in. Designed to navigate treacherous conditions like those in front of a glacier, NUI was recruited to the project to conduct surveys and retrieve samples, including seafloor cores, within just a few feet of the ice.

For NUI’s pilots however, the sediment plumes pouring out of Kangerlussuup Sermia were an unexpected challenge, leaving the submersible blind at the underwater coring sites. With zero visibility at the seafloor, the pilots came up with a novel approach, a maneuver they nicknamed ‘bumblebee coring.’ It works by having NUI rise to clearer waters where the pilots could see enough to position a coring tube, and then having all of NUI’s 5,000 pounds drop to the seafloor. They then directed NUI’s robot arm to push the coring tube into the dirt.

The approach has delivered samples of seafloor layers from the very foot of the glacier to the TERMINUS scientists’ on-board labs.

Back on the Celtic Explorer, Pascual is grinding up and organizing pieces of the NUI cores. Once the vessel returns to port, these will be sent off to labs where they’ll be dated and examined. The age of that mud will help fill in important pieces of a  glacial sediment puzzle that could help reveal the fate of Greenland’s ice sheet in a warming world.

The weary crew have hauled the last core on deck just as Greenland’s morning sun rises over the glacier. Soon the day shift will be on duty, the night shift will go to bed, and the vessel’s deck will prepare NUI for another voyage to the deep.