Joint Amazon River Plume Mixotrophy Study

• Applicants: Professor Dr. Thorsten Dittmar; Professor Dr. Rainer Kiko; Professorin Dr. Andrea Koschinsky; Dr. Natalie Loick-Wilde
• Subject Area: Oceanography
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564898126

Carbon sequestration and fisheries are closely linked ecosystem services of large tropical river plumes in a heterotrophic, oligotrophic tropical ocean, but the controls on the processes regulating these services are largely unclear. There is an urgent need for a fundamental understanding of the function of large tropical river plumes in the global nitrogen and carbon cycle, before these ecosystems become degraded due to global warming and anthropogenic stressors such as dams, deforestation and eutrophication. Model results show that mixotrophy has a so far unconsidered key function compared to pure autotrophy, as it increases energy transfer to the higher trophic levels in marine food webs, favors carbon sequestration by converting dissolved organic matter (DOM) pools into refractory compounds, and promotes export production through increased primary and secondary production in marine ecosystems. Empirical data confirming the model results in the field are still lacking, as the identification of mixotrophy in the field is difficult. Trophic isotope proxies from seston now show for the first time a dominance of mixotrophy in the outer edge of the Amazon plume, where the river water is about 27 days old. Here, mixotrophy appears to be the optimal strategy for growth and part of the succession of functional diversity of phytoplankton along the aging plume. The JAmaMix project will provide crucial insights into how physical processes and biogeochemical gradients at small, submesoscale and mesoscale levels promote mixotrophy of various planktonic organisms, including marine fungi. The ultimate goal is to show how mixotrophy influences primary, secondary and export production and thus carbon sequestration and fisheries in the Amazon plume.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 2520: Infrastructure area - Research Vessels
• Co-Investigators: Isabell Klawonn, Ph.D.; Dr. Volker Mohrholz