Marine Biogeochemistry

Nitrogen fixation

The marine nitrogen inventory is determined by a balance between nitrogen fixation and nitrogen loss via denitrification and ANAMMOX. While nitrogen loss occurs primarily in low oxygen waters, the distribution of nitrogen fixation in the global ocean seems to be determined by various factors, including the availability of excess phosphorus and iron, surface layer mixing depth and temperature. Nitrogen-fixing (diazotrophic) cyanobacteria also seem highly sensitive to ocean acidification, with increasing rates of carbon and nitrogen fixation and higher cellular C:N:P ratios at elevated pCO2. Rising surface ocean temperature, ocean acidification and the enhanced loss of bioavailable nitrogen in a deoxygenating ocean together may widen the ecological niche for N-fixing cyanobacteria in the ocean. Our research in this area focuses on the distribution of diazotrophic cyanobacteria in relation to the environmental conditions, on their responses to ocean change and their regional to global contribution to nitrogen cycling, using a range of observational, experimental and modeling approaches (SFB754SOPRANBIOACID)