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.

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. 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. 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. This process is key to the “biological carbon pump,” an important part of the global carbon cycle.

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. Like plants, these single-celled floating organisms use photosynthesis to turn light into energy, consuming carbon dioxide and releasing oxygen in the process. Every spring in the Northern Hemisphere, the ocean surface erupts in a massive bloom of phytoplankton.

Carbon cycle ocean