Molecular underpinnings and biogeochemical consequences of enhanced diatom growth in a warming Southern Ocean

Significance Phytoplankton contribute to the Southern Ocean’s (SO) ability to absorb atmospheric CO 2 and shape the stoichiometry of northward macronutrient delivery. Climate change is altering the SO environment, yet we know little about how resident phytoplankton will react to these changes. Here, we studied a natural SO community and compared responses of two prevalent, bloom-forming diatom groups to changes in temperature and iron that are projected to occur by 2100 to 2300. We found that one group, Pseudo-nitzschia , grows better under warmer low-iron conditions by managing cellular iron demand and efficiently increasing photosynthetic capacity. This ability to grow and draw down nutrients in the face of warming, regardless of iron availability, has major implications for ocean ecosystems and global nutrient cycles.