Hidden biological processes slow the ocean's carbon storage

New research led by Stanford University reveals a previously unknown factor that could change how we understand the ocean's role in fighting climate change. The study, published on October 11 in 'Science', identifies mucus "parachutes" created by microscopic marine organisms that dramatically slow their sinking, a key process in the ocean's ability to remove carbon dioxide from the atmosphere. This discovery suggests earlier estimates of the ocean's carbon sequestration may have been overestimated but also opens the door to improving climate models and guiding policymakers in tackling climate change.

"We haven't been looking the right way," said Manu Prakash, senior author of the study and associate professor of bioengineering at Stanford. "What we found underscores the importance of fundamental scientific observation and the need to study natural processes in their true environments. It's critical to our ability to mitigate climate change."

The biological pump
Marine snow, a blend of dead phytoplankton, bacteria, and organic material, helps absorb roughly one-third of human-made carbon dioxide and sinks it to the ocean floor, where it remains for thousands of years. This process, known as the biological pump, is essential to the ocean's carbon storage, yet how these particles fall through the ocean's vast depths has been largely unknown - until now.

Using a rotating microscope developed in Prakash's lab, which simulates the natural movement of these organisms in water, researchers were able to observe this process in real-time at sea. By collecting marine snow in traps and analyzing it immediately, they observed a surprising effect - mucus parachutes formed by the organisms slowed their sinking and kept them longer in the ocean's upper layers, giving microbes more time to break down the carbon they carry. This slows the absorption of carbon dioxide into the ocean.

Complex natural processes
Study lead author Rahul Chajwa, a postdoctoral scholar in Prakash's lab, explained, "Theory tells you how a flow around a small particle looks like, but what we saw on the boat was dramatically different. We are at the beginning of understanding these complex dynamics."

The researchers emphasize the importance of conducting observations in natural environments. "We cannot even ask the fundamental question of what life does without emulating the environment that it evolved with," Prakash noted. He urged scientific funding organizations to prioritize research that focuses on observing life as it exists in nature, not just in controlled lab environments.

The study highlights how seemingly simple natural processes, like the descent of marine snow, can have a profound impact on our world, much like how sugar dissolves in coffee.

Looking ahead, the team is refining their models and integrating their findings into larger Earth-scale models. Their data, collected over six global expeditions, will form the largest dataset on marine snow sedimentation, contributing significantly to future research on ocean carbon sequestration.

Despite the challenges this discovery presents, Prakash remains hopeful. "Every time I observe the world of plankton via our tools, I learn something new," he said, pointing to recent findings off Northern California that suggest other processes might accelerate carbon sequestration.

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