Joint press release of Helmholtz Centre Hereon and GEOMAR Helmholtz Centre for Ocean Research Kiel
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-Zentrum 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 in the journal Nature Climate Change.
Seas and the ocean are one of our largest carbon sinks. Every year, they absorb around 30 per cent 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 Centre for Ocean Research Kiel and the Earth SURFACE System Research Center, Japan, the team of authors analysed 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 Prof. Dr. Kai Wirtz, lead author of the study and ecosystem modeller at the Hereon Institute of Coastal Systems – Analysis and Modelling. (Source: Press Release Hereon/GEOMAR)
Read the complete joint press release of Hereon/GEOMAR:
==> Do oceans absorb more CO2 than expected?
Wirtz, K., Smith, S.L., Mathis, M., & Taucher, J. (2022): Vertically migrating phytoplankton fuel high oceanic primary production. Nat. Clim. Chang. (2022), doi:10.1038/s41558-022-01430-5
Abstract:
Marine net primary production (NPP) is remarkably high given the typical vertical separation of 50–150 m between the depth zones of light and nutrient sufficiency, respectively. Here we present evidence that many autotrophs bridge this gap through downward and upward migration, thereby facilitating biological nutrient pumping and high rates of oceanic NPP. Our model suggests that phytoplankton vertical migration (PVM) fuels up to 40% (>28 tg yr−1 N) of new production and directly contributes 25% of total oceanic NPP (herein estimated at 56 PgC yr−1). Confidence in these estimates is supported by good reproduction of seasonal, vertical and geographic variations in NPP. In contrast to common predictions, a sensitivity study of the PVM model indicates higher NPP under global warming when enhanced stratification reduces physical nutrient transport into the surface ocean. Our findings suggest that PVM is a key mechanism driving marine biogeochemistry and therefore requires consideration in global carbon budgets.