Aboard a drilling rig in the Mediterranean, scientists seek to understand Earth’s past climates

UChicago geologist spent two months at sea extracting rock cores to recreate history of climate

Editor’s note: This story is part of Dispatches from Abroad, a series highlighting UChicago community members who are researching, studying and working around the world.

Aboard the ship JOIDES Resolution are 30 scientists, 85 crew members, 460 pounds of coffee, hundreds of pieces of million-year-old rock, and one very big drill.

The mission: Catalogue the history written into the layers of rock below the Mediterranean Sea and the Atlantic Ocean to understand how our world changes over time.

“So much of our understanding of the world comes from these cores of rock from the seafloor,” said University of Chicago geologist Clara Blättler. “They even helped prove the theory of plate tectonics itself. They are really invaluable.”

The oceans that cover the vast majority of Earth play a huge role in the climate, but their depths hold information about more than just the sea.

The story of the world is recorded at the bottoms of the oceans: the fall of mountains as they’re washed down rivers a pebble at a time, the rise of new species as their dead fossilize, the changing of major ocean currents and the advance and retreat of glaciers.

That’s why Blättler spent two months at sea aboard the JOIDES Resolution last winter, crammed into a tiny cabin and working 12-hour shifts alongside several dozen other scientists from around the world. With the drill, the scientists can retrieve long, thin cores of the mud and rock below the ocean, each a little over two inches in diameter. Each one is a cross-section of the seafloor, with layers deposited bit by bit over the last several million years that can tell scientists what happened there. 

There are many questions that these cores can help answer, but for this particular JOIDES Resolution expedition, the first one in line is an event known as the Messinian Salinity Crisis.

A story in salt

Six million years ago, the Mediterranean Sea suddenly became a lake. The strait normally connecting it to the Atlantic Ocean was cut off: maybe by tectonic plates moving, changes in global sea level, or some combination.

What’s indisputable is that things got hairy for everything living in the newly minted lake. Without regular water flow from the ocean, the whole sea slowly began to evaporate—and what was left behind got saltier and saltier.

“You can see it in the cores—you come to a layer nearly a kilometer thick that’s just salt,” said Blättler, an assistant professor of geophysical sciences. “There are no fossils in this layer; much like the Dead Sea today, nothing bigger than a microbe could survive in these waters.”

The Messinian Salinity Crisis killed a lot of fish locally, but scientists think it likely affected the global climate as well.

“The water that flows out of the Mediterranean today is saltier than the Atlantic, and that contributes to the North Atlantic being saltier and denser than it otherwise would be—which contributes to the global ocean circulation,” explained Blättler.

Eventually, after about half a million years, the strait opened up again—possibly in one huge flood—and normal marine life returned. But the saga is particularly of interest to scientists right now because the entire Mediterranean region is forecast to become more arid as climate change progresses. The sea is already measuring a little saltier than it was two decades ago, Blättler said.

“So as this changes, we want to be prepared to understand all the processes and implications,” Blättler said. “By understanding this really extreme event, we can learn more about how these processes influence climate as a whole.”

Midnight to noon

When the JOIDES Resolution drill gets going, there’s no time for anything else.

For virtually the entire two months the ship is at sea, the drill is working. That’s round the clock. Everyone pulls a twelve-hour shift, sharing a tiny cabin with someone on the opposite shift.

When the cores come off the drill, technicians cut them into five-foot sections that are carried into the ship to the lab. There, the scientists scan and measure the properties of each core, split the rock in half to describe everything they see, and check for fossils to get a sense of the age of the core. (They’ll be more precisely dated later.)

At its fastest, the scientists have just 45 minutes to get the cores safely stored and recorded before the next one comes up from the drill. 

“I was on the midnight to noon shift,” Blättler said. “You get up, eat breakfast before you go on shift—then there’s a few meal breaks over the course of the shift, but otherwise, it’s usually pretty nonstop. Then afterwards, you have about an hour to yourself to maybe take a quick walk on the deck, check your email, or call your family before you have to go to sleep again.

“It’s pretty intense. But it’s worth it because this is the only way we have to answer a lot of these scientific questions.”

‘People will be learning from these for generations’

Even though they only got a cursory look at the cores during the expedition, the scientists can already tell it was worth it.

“We still have to run a lot more analysis, but we can already say the mission was extremely successful,” said Blättler. “We were able to get much more continuous records of the timeline than we’d even hoped for.”

Now, months later, scientists can start analyzing the cores in earnest. They will be dated and the overlaps matched up, to create a comprehensive timeline going back millions of years.

Some of the material will be pulverized and analyzed; for example, Blättler’s lab will investigate the composition of the carbonate minerals in the cores to see how the makeup of the sea inside and the ocean outside changed over time.

But just as NASA has saved part of the precious moon rock samples from the Apollo missions for future studies, half of the sediment cores will be set aside for the future when new technologies will be invented.

“People will be learning from these for generations,” Blättler said. She herself recently analyzed samples from the 1970s as part of a scientific study, using techniques that didn’t exist yet when those cores were collected.  

This is Blättler’s second turn aboard the JOIDES Resolution. Each mission is different, she said, but it’s worth it.

“Aboard this ship you have 30 scientists from different countries, with different expertise, and we’re always learning from each other,” she said. “And we’ll be working together for years to come to interpret the results. It’s a wonderful international collaboration.”