The Southern Ocean stores 40 percent of the carbon dioxide that we humans produce - more than any other ocean on Earth. Phytoplankton is one of the main reasons for that: The microorganisms take up CO2 during photosynthesis. But although the Southern Ocean is rich in nutrients that support their growth, there is little phytoplankton there. One reason for this is a lack of iron in the water. However, a recent study by the Alfred Wegener Institute, the University of Bremen and Bremerhaven in the journal Nature Communications Biology, now shows that manganese also plays a crucial role for phytoplankton in the Southern Ocean.
Oceans are among the largest carbon sinks on our planet. Just below the water surface, phytoplankton, absorb carbon dioxide from the atmosphere through photosynthesis. In addition to light and nutrients such as nitrates or phosphates, trace elements also influence the growth and species composition of phytoplankton. How the presence or lack of elements like iron and manganese affect microorganisms in the Southern Ocean, has been studied by a research team led by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). In the Drake Passage, the scientists took water samples and observed how phytoplankton developed when iron, manganese and a combination of both trace elements were added.
"The organisms responded quite differently," says Jenna Balaguer, a doctoral student at AWI and lead author of the study. "Most phytoplankton species grew the most when iron was added. However, the two species most prevalent in the Drake Passage responded the most to the combination of iron and manganese." This highlights that not all phytoplankton species need the same amount trace elements for growth. Rather, each species has specific requirements, so the lack of single trace elements has different effects. "The effects of possible co-limitation of iron and manganese on specific microorganisms have been poorly studied," says Jenna Balaguer. "However, this is a key factor in understanding the structure of the phytoplankton community in the Southern Ocean." This is important because the Southern Ocean is experiencing drastic climatic changes in the future. The ability to store carbon would then depend on how much iron and manganese are available and this would have consequence on phytoplankton community structure and therefore how much carbon is taken from the surface to the bottom of the ocean. “Therefore, the influence of manganese on phytoplankton must definitely be considered in the assessment of future changes in the Southern Ocean, because this region is of great importance for climate regulation," emphasizes Jenna Balaguer.
Originalpublikation
Balaguer, J., Koch, F., Hassler, C. et al. Iron and manganese co-limit the growth of two phytoplankton groups dominant at two locations of the Drake Passage. Commun Biol 5, 207 (2022). https://doi.org/10.1038/s42003-022-03148-8