2024 Articles

Nitrate Uptake and Primary Production Along the Amazon River Plume Continuum

Umbricht, Jacqueline; Burmeister, Christian; Dippner, Joachim W.; Liskow, Iris; Montoya, Joseph P.; Subramaniam, Ajit; Voss, Maren

The Amazon River is thought to deliver important nutrients to the Western Tropical North Atlantic, which enable high phytoplankton growth and especially favor nitrogen fixers. Previous studies have focused on nitrogen fixation, but we propose that other nitrogen sources could also be important in the river plume to support the high phytoplankton growth there. In this study, we measured the uptake of nitrate by phytoplankton in the plume for the first time. We found that nitrate uptake is of variable importance for phytoplankton growth in the Amazon River plume; it seems to be more important close to the river mouth, where diatoms and dinoflagellates dominate, compared to the northern plume, where nitrogen fixers are dominant. Investigations like this will help us to better understand, which nitrogen sources are important for the growth of different phytoplankton species in the plume. With this information, we can improve predictions of competition of phytoplankton species for nitrogen and their general growth in the future. Some phytoplankton groups have a higher potential to contribute to oceanic CO2 storage than others, so understanding the future of these phytoplankton groups is critical to any assessment of the amount of CO2 that can be stored by the ocean.