Thursday August 4, 2022


Phytoplankton need light and nutrients to grow. The microscopic algae rarely find both at the same time in sufficient quantities in the ocean. In the upper water layers, they usually lack nutrients, and further down, they lack light. A new study led by the Helmholtz Center Hereon now says: Phytoplankton can migrate back and forth between deeper layers and the water surface. If this were confirmed, it would have enormous consequences for the calculations of the natural carbon pump and thus for current calculations of the carbon budget. The study’s results were published today in the journal Nature Climate Change.

Seas and the ocean are one of our largest carbon sinks. Every year, they absorb about 30% of the CO2 produced by humans and thereby remove it from the atmosphere. This is mainly thanks to phytoplankton. With the help of light and nutrients, these microscopic plants take up the carbon dioxide and release oxygen. Until now, researchers assume that phytoplankton hardly move by themselves, but are driven along by currents. A study led by the Helmholtz-Zentrum Hereon now presents arguments that question this assumption. For this publication, which also involves GEOMAR Helmholtz Center for Ocean Research Kiel and the Earth SURFACE System Research Center, the team of authors analyzed numerous empirical research results. The conclusion: the measured data cannot be explained by the passive movement of phytoplankton. On this basis, the scientists developed a new model that includes the vertical migration of phytoplankton and can thus calculate the active “pumping up” of nutrients.

“Previous models treat phytoplankton as passive particles, while a lot of evidence suggests that it actively migrates to take up carbon in upper layers via photosynthesis and to store nutrients in lower layers,” says Kai Wirtz, lead author of the study and ecosystem modeler at the Hereon Institute of Coastal Systems, Analysis and Modeling.

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