The Ocean’s ‘Biological Pump’ Captures More Carbon Than Expected

Every spring in the Northern Hemisphere, the ocean surface erupts in a massive bloom of phytoplankton. Like plants, these single-celled floating organisms use photosynthesis to turn light into energy, consuming carbon dioxide and releasing oxygen in the process. When phytoplankton die or are eaten by zooplankton, the carbon-rich fragments sinks deeper into the ocean, where it is, in turn, eaten by other creatures or buried in sediments. This process is key to the “biological carbon pump,” an important part of the global carbon cycle.

Scientists have long known that the ocean plays an essential role in capturing carbon from the atmosphere, but a new study from Woods Hole Oceanographic Institution (WHOI) shows that the efficiency of the ocean’s “biological carbon pump” has been drastically underestimated, with implications for future climate assessments.

In a paper published April 6 in Proceedings of the National Academy of Sciences, WHOI geochemist Ken Buesseler and colleagues demonstrated that the depth of the sunlit area where photosynthesis occurs varies significantly throughout the ocean. This matters because the phytoplankton’s ability to take up carbon depends on amount of sunlight that’s able to penetrate the ocean’s upper layer. By taking account of the depth of the euphotic, or sunlit zone, the authors found that about twice as much carbon sinks into the ocean per year than previously estimated.

Read more at Woods Hole Oceanographic Institution

Image: Marine chemist Ken Buesseler (right) deploys a sediment trap from the research vessel Roger Revelle during a 2018 expedition in the Gulf of Alaska. Buesseler's research focuses on how carbon moves through the ocean. Buesseler and co-authors of a new study found that the ocean's biological carbon pump may be twice as efficient as previously estimated, with implications for future climate assessments. (Credit: Photo by Alyssa Santoro, © Woods Hole Oceanographic Institution)