First study to quantify the total carbon sequestration for a region of the ocean

Researchers at Florida State University have analyzed the carbon exported from surface waters of the California Current ecosystem — the first-ever study to quantify the total carbon sequestration for a region of the ocean.

The study, published in Nature Communications, serves as a framework for assessing how the processes that sequester carbon might change in a warmer world, while also creating a blueprint for similar budgets in other ocean regions.

Understanding the carbon cycle — the sources and reservoirs of carbon — is an important focus of Earth sciences. Many studies have examined the carbon sequestered by sinking particles formed from algal production. Fewer studies have focused on plankton particles that move to the deep ocean through other methods, or marine life that migrates vertically through layers of the ocean.

"Our study is the first to put all of these different processes together to fully investigate the processes driving the biological carbon pump for a major ocean region," said lead author Michael Stukel.

Stukel and his team found that a host of processes contribute to the movement of organic carbon through the marine ecosystem. Their analysis confirmed that sinking particles are the dominant process transporting carbon, but they also found that particles transported by ocean currents and zooplankton that migrate down into the deep ocean every day contribute 30% to 40% of carbon sequestered in the deep ocean.

The data come from 15 years of research cruises by scientists affiliated with the U.S. National Science Foundation-supported California Current Ecosystem Long-Term Ecological Research site, an area that spans waters from San Diego to Monterey Bay. The researchers combined information collected during those trips with computer modeling.

Algae in the surface ocean perform about half the world's photosynthesis, but they live for a week, so the carbon dioxide they take in only gets sequestered when the bodies of these plankton sink to the deep ocean, part of a process known as the biological carbon pump. The main point of this study was to quantify all components of the biological pump, including algal sinking.

As climate change alters Earth, it's unclear how it might affect processes like the biological carbon pump.

"We don't know if the biological carbon pump will take up more or less carbon dioxide in the future," Stukel said. "The first step in answering that question is putting together a full 'budget' for what's happening now. We think our study is an important step in the process of understanding how the biological carbon pump works today and how it will change in the future."

Added Cynthia Suchman, a program director in NSF's Division of Ocean Sciences, "This research synthesizes the ways ocean biology can influence the carbon cycle of the California Current. It's a terrific example of how long-term studies help us predict how the ocean and earth system might respond to climate change."