Rare-earth metal reveals ancient ocean currents linked to climate triggers

Rare-earth metal reveals ancient ocean currents linked to climate triggers

By Marisa Sloan, Dec. 18, 2020 –

Despite the sci-fi name of this rare-earth element, neodymium is actually pretty common. The silvery metal is used in everything from cell phones and wind turbines to tanning booths and electric guitars.

But it’s the neodymium found thousands of meters below the ocean’s surface that captured the interest of Dr. Sophie Hines, a postdoctoral research fellow at Columbia University’s Lamont-Doherty Earth Observatory.

Hines traced the metal trapped within ancient marine sediments to reconstruct changes in ocean circulation reaching as far back as one million years ago. She presented her research at the Comer Climate Conference, an annual meeting of climate scientists that was held virtually this October.

“The ocean neodymium cycle is something that people have been studying for a long time,” she said. “But there are still parts that we’re learning.”

Because the global ocean circulation system brings water from the surface down to the deep ocean, it is thought to play an important role in trapping atmospheric carbon dioxide and triggering global climate changes.

According to Hines, different forms of neodymium wind up in the ocean through the weathering of various rocks and minerals. The neodymium composition of the North Atlantic Ocean, which is characterized by older continental crust, is distinct from that of the Pacific Ocean, which has more volcanoes and newly erupted material. These differences make it easier for climate scientists to trace the movement of seawater away from its sources and reconstruct changes in deep ocean currents.

“Trying to figure out how the ocean impacted climate in the past is interesting in and of itself,” Hines said. “But it also serves as an important calibration data set to make sure that the models we’re using to look at future climate change are accurate.”

Right now, the oceans provide a huge “carbon sink,” absorbing much of the carbon dioxide emissions from fossil fuels that are warming the planet at a threatening pace. The less carbon dioxide there is in the atmosphere, the colder the planet becomes.

According to a 2019 report by the Intergovernmental Panel on Climate Change, smaller glaciers will melt by more than 80% by the end of the century if greenhouse gas emissions continue on their current trajectory. The resulting influx of fresh water will likely disrupt ocean currents and, by extension, the climate in a way humans have yet to see.

Even if emissions were stabilized tomorrow, it would take many years for the oceans to adjust to the 1° C rise in global temperatures that has already occurred.

In 2016, Hines joined a two month-long deep-sea drilling expedition to South Africa’s Cape Basin on a whim when another researcher couldn’t make the trip. Although she was wrapping up the final year of her PhD program, she had yet to work in the field and didn’t know what to expect.

Location map of Integrated Ocean Drilling Program Site U1479, approximately 85 nautical miles southwest of Cape Town, South Africa
Location map of Integrated Ocean Drilling Program Site U1479, approximately 85 nautical miles southwest of Cape Town, South Africa. Water in this region comes from a complex mix of sources, including the North Atlantic, Indian and Southern Oceans. (Marisa Sloan/MEDILL)

“I was on the day shift, which [was] from noon until midnight,” Hines said. “Every day we did all this science, and then in the time we had off we hung out and watched movies and watched the stars at night.”

The first few weeks were new and exciting, she said. Each scientist onboard had his or her own tasks to do, ranging from dating the 9-meter-long sediment cores by their micro-fossils to squeezing water out of them with a hydraulic press.

By the time the sixth week rolled around, however, everyone was stepping on each other’s toes.

“Then we made it to Cape Town and had a big party,” she said, laughing. “I remember being most excited to have a beer and eat a salad by the end.”

The Cape Basin, where Hines traveled in search of ancient sediment cores, lies in The South Atlantic Ocean between the North Atlantic and the Pacific. Her chemical analysis shows a shift toward more Pacific-like water in the area during the last glacial period, from approximately 110,000 to 12,000 years ago⁠, perhaps revealing an ocean circulation that sequestered carbon dioxide-rich water in the Pacific and stored it in the South Atlantic.

Bob Anderson, a founder of the international program GEOTRACES and professor at Columbia’s Lamont-Doherty Earth Observatory, said her results correlate well with similar studies on carbon and carbonate ions.

“I agree [with Hines], but I don’t think we can make that as a final conclusion yet,” he said. “We know from a lot of neodymium data coming out right now that it’s more complicated than people used to think.”

In fact, another study published earlier this year posits an opposite conclusion. It suggests the changes in neodymium concentration in the South Atlantic may actually be a result of changes in the North Atlantic, rather than a switch to water from the Pacific.

“What I think we need are more records from the shallow to mid-depth North Atlantic and from the Pacific,” Hines said.

That’s the goal of Anderson’s program GEOTRACES, which is designed to study traces of neodymium and a barrage of other elements found within all of the earth’s major ocean basins. So far, scientists from approximately 35 nations have been involved in the expeditions to better understand how the chemical environment affects ecosystem function and vice versa.

Anderson said he expects those mysteries will be better understood in the next few decades, although he will likely be cheering on scientists like Hines from the sidelines by then.

“It will take combining the data that I collected with other people’s data to try and get a more holistic understanding of what happened,” Hines said. “That’s the hard part. And it’s also the fun part.”

Marisa Sloan is a health, environment and science reporter at Medill. You can follow her on Twitter at @sloan_marisa.

56-million-year-old algae could shed light on future climate change

56-million-year-old algae could shed light on future climate change

By Marisa Sloan, Dec. 17, 2020 –

Faced with a challenge as mammoth as climate change, scientists are turning to some very tiny organisms for insight — coccolithophores, the single-celled algae that are smaller than a grain of sand.

In order to grow, algae use sunlight to convert carbon dioxide and water into energy in a process called photosynthesis that all plants employ. The algae prefer to take up the lightest of two different forms of carbon, but sometimes resort to the heavier form when carbon dioxide levels in the surrounding water are low.

Louis Claxton, a Ph.D. student at the University of Oxford, uses the ratio of light to heavy carbon trapped in the algae’s fossilized shell to approximate the amount of carbon dioxide in the ocean when it lived. He presented his research at the Comer Climate Conference, an annual conference of global climate scientists that was held virtually this October.

“These things are gorgeous to look at under the microscope,” Claxton said. “And something so small, something that no one really pays much attention to, can hold so much information about our past.”

Right now he examines algae from a period in Earth’s history called the Eocene, which lasted from approximately 34 to 56 million years ago. It was a time marked by hot temperatures, rapid changes in climate and a lack of permanent ice sheets. This was the last such extreme heat spell Earth experienced and scientists believe the period could hold important implications for where today’s warming climate is heading.

“If we can understand how biology responded to changes in carbon dioxide over this period, we may be in a better place to understand how it may change in the future,” Claxton said.

And it is changing.

According to the Intergovernmental Panel on Climate Change, the current amount of atmospheric carbon dioxide exceeds measurements from at least the past 800,000 years. That increase, at a rate unprecedented in modern history, has largely been caused by the burning of fossil fuels and led to surging global temperatures, rising sea levels and severe weather patterns.

“In dealing with these big issues, the history of climate is absolutely essential,” Dr. Richard Alley, a geoscientist at Pennsylvania State University, said during the conference. “History gives us a way to test models.”

By growing algae in his lab and subjecting them to various levels of carbon dioxide, Claxton can create models that predict how ancient algae reacted to similar changes in carbon dioxide levels.

“They are nightmare pets because they are very sensitive to temperature and all sorts of things,” he said. “But I’ve been looking after them for about three or four years, and I’ve gotten quite attached to them.”

Sophie Gill, another Ph.D. student within Claxton’s research group, knows all about that.

“I work on slightly different species because some of the species I work on weren’t evolved during the time that he works on,” she said. “But we’re able to see a common ground [in that] some coccolithophores are not able to cope with very high levels of dissolved [carbon dioxide].”

Gill is currently trying to find the perfect oceanic conditions that will allow the algae to take up more carbon dioxide through photosynthesis than they produce via their calcium carbonate shells. She hopes the algae may someday be used as a more effective carbon sink, absorbing large amounts of carbon dioxide from the ocean’s surface and trapping it within their fossils when they die.

The concept seems ideal on the surface, but Claxton is digging into the past — literally — for any unintended consequences it could have.

“The samples come from about 1,500 meters deep off the coast of Namibia,” he said. “If you were to hold some of the sediment that I was working with in your hand, it looks like… slimy mud that someone’s dug up from the bottom of a puddle.”

Hidden within that mud, however, are the fossilized remains of algae that lived tens of millions of years ago. When Claxton compares their carbon composition to his models, he is able to estimate the carbon dioxide levels in the ocean, and by extent the atmosphere, at the time the algae lived.

So far, his calculations correspond well with existing data from various other methods. Now that Claxton has proven the concept works, he’s ready to jump into the unknown: time periods in the even farther past for which there are no well-constrained data.

“The method that I’m working on to reconstruct carbon dioxide could potentially go back about 200 million years,” he said, referring to how long ago this particular type of algae evolved.

In comparison, ice core records extend to only about 800,000 years.

“We may be missing analogs in Earth’s history that are almost identical to today,” Claxton said. “By identifying those periods, we can perhaps understand what the future may hold.”

Marisa Sloan is a health, environment and science reporter at Medill. You can follow her on Twitter at @sloan_marisa.

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