Tapping into the ocean to combat climate change

Chloe Dean traces her decision to go to graduate school to the day a wildfire blazed through southern Oregon.

At the time, Dean was working as a lab technician at a hemp-processing startup in Oregon. She had studied environmental science as an undergraduate at the Oregon Institute of Technology but fell in love with chemistry. Working at the company was a good way to keep her lab skills sharp.

Meanwhile, Oregon was experiencing its worst forest fire season in living memory. On September 8, 2020, the Almeda fire swept through Rogue Valley, destroying 2,600 homes in a single morning. Dean was living 15 miles down the road.

For her, the fire was a wake-up call. It became “really hard for me to justify continuing working at this cannabis company,” she says. She’d been considering grad school, and that clinched it. So she ramped up her search for a program that would let her use her chemistry background to help combat climate change. She found it at Adam Subhas’s lab at the Woods Hole Oceanographic Institution (WHOI) in Falmouth, Massachusetts, and in 2021 she signed on as the lab’s first graduate student.

Dean is now in her third year in the joint MIT-WHOI program, where she is studying ocean chemistry and working toward her lab’s lofty goal: turning the ocean into a weapon against climate change.

Ocean acidification

The ocean serves as a vast reservoir of carbon, holding about 50 times more than the atmosphere does. And it plays a crucial role in the way carbon moves around on our planet. For example, seawater absorbs carbon dioxide from the atmosphere through molecular diffusion in colder waters such as those at high latitudes and releases it from warmer tropical waters. Biological mechanisms are also in play as photosynthetic plankton take in carbon dioxide and as dead organisms sink to the ocean floor and turn into carbon-rich sediment. All these processes, and many others, make up the oceanic carbon cycle.

Around 31% of all the carbon humans have emitted has dissolved into the ocean, and this dissolved carbon has driven up the ocean’s acidity by 30% in the last 200 years. Ocean acidification, as this phenomenon is called, dissolves shells, limits growth of coral reefs, and ultimately threatens to disrupt food chains on a massive scale. And it’s feared that when the ocean becomes overly acidic, its ability to absorb carbon could diminish—and the ocean might even begin to release more into the atmosphere.

But the ocean has ways of fighting back.

Dean first began studying ocean acidification as an undergrad when she spent a summer at the University of California, Santa Barbara, researching how the phenomenon affects kelp. To her surprise, she found that the geochemistry of kelp forests makes them naturally resistant to acidification. The sediment around the seaweed is full of alkaline minerals that, when dissolved in the carbon-rich water, increase the water’s alkalinity to offset the acidity of the carbon.

Dean (left) works with WHOI colleagues Kate Morkowski and Lukas Marx onboard a research vessel to set up an experiment that will incubate phytoplankton in seawater with different levels of alkalinity. The goal is to understand how adding alkaline materials to the ocean would affect them.COURTESY PHOTO

This neutralization process forms the basis of Dean’s research today. The Subhas lab studies the oceanic carbon cycle, which includes this “canceling out” of dissolved carbon by dissolved alkaline minerals. As sediment dissolves and alkalinity increases, the ocean is able to pull more carbon dioxide from the atmosphere. Over millions of years, this keeps atmospheric carbon in check.

“The ocean has a bad case of heartburn,” Subhas says. “What we’re talking about is giving it Tums.”

But what if you could accelerate that process on a large scale by introducing vast quantities of alkaline substances like lime to the ocean? Theoretically, it could help mitigate acidification. Researchers are now giving the idea, first proposed in the 1990s, serious consideration. “The ocean has a bad case of heartburn,” Subhas says. “What we’re talking

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By: William von Herff, SM ’23
Title: Tapping into the ocean to combat climate change
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Published Date: Tue, 24 Oct 2023 21:00:00 +0000

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