Science, Tech & Environment

Tracing the Ocean's Ingredients

You can think of the world's oceans as a kind of rich broth. They're full of salt, of course, but they also contain other ingredients, many of them vital to marine life and to the processes that control the Earth's climate. Reporter Ari Daniel Shapiro of our partner program NOVA met up with a French scientist who's studying the chemistry of seawater for clues to our planet's future.

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Catherine Jeandel leads me into a narrow cellar. It's cold. She secures her turquoise scarf and admires the bottles of liquid lining the walls. "It looks like wine," she says.

Ocean Vintage

Although we're in Toulouse, France — a region of vineyards — this is no wine cellar. These bottles are filled with ocean water.

"We have vintage from the Atlantic, vintage from the Pacific, vintage from the Indian Ocean," she says with a smile. "Vintage from everywhere in the world."

Jeandel is an oceanographer at CNRS — the French national research labs. She shows me a water sample collected almost 4,000 miles off Papua New Guinea. Another was taken off Mexico from a mile below the surface.

To the untrained eye, the water all looks the same, but Jeandel sees things differently.

Back in her office, she shows me her coffee mug. It displays the periodic table of the elements.

"Each element has its own life, own behavior," she says. "They are all different. And some of them can tell you a story, and some of them cannot."
Clues from Neodymium

Jeandel works with elements that tell her stories about how the ocean works.

She spends a lot of time these days focusing on neodymium. It's a silvery metal — number 60 on the periodic table — and it offers Jeandel clues to where ocean water has been, and how it got there.

Traces of neodymium can be found in rocks all over the world, but depending on where you look, you find different types of neodymium. Some of it is just a little heavier, some of it is just a little lighter. To Jeandel, the different neodymium isotopes are like pigments of paint.

"You have to imagine that the Earth is like a mosaic of different colors," she says.

And these different colors get swept into the ocean. "It's like painting the seawater."

Jeandel is trying to piece together where all that "paint" came from.

Oceanographers already knew that the chemistry of the ocean is influenced by what washes off the land from rivers and what blows out to sea as dust. But when Jeandel studied the neodymium in her collection of seawater, she arrived at a kind of eureka moment.
A Eureka Moment

"The big surprise was when we realized that the seawater, when it was going close to the coast, was changing color."

Jeandel discovered that the bottom of the ocean, extending up to 100 miles from shore, is also contributing to the chemistry of our seas. Vast swaths of the seafloor close to shore are slowly dissolving into the ocean and liberating neodymium into the water.

And it's not just neodymium being released. This section of the sea bottom is contributing other elements into the sea as well — like iron and silicon, which are critical to many forms of marine life.

Jeandel's finding is also forcing a reevaluation of toxic waste that's been buried just offshore. Her discovery suggests these contaminants could end up getting released into the ocean.

Jeandel's work with neodymium and a growing list of other elements is also helping to improve computer models of ocean circulation and the movement of carbon around the Earth. Those models are crucial for understanding how climate change and ocean acidification will affect our planet.

Jeandel says there are still a lot of questions to answer. "We took just a small part of the curtain and we lifted it."

She intends to continue pulling back that curtain, uncorking more of her bottles that contain the world's oceans.

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    Marine geochemist Catherine Jeandel. (Photo: Ari Daniel Shapiro)

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    The oceans 'painted' with neodymium. Heavier neodymium (from older rocks) is shown in blue and purple. Lighter neodymium (from younger rocks) is red. (Photo: Courtesy of Thomas Arsouze)