will nitrogEn fiXaTion offset nitrogen dePletion in expAnding oceaN Deserts? (EXPAND)

Summary of the project

The warming and nutrient depleted conditions induced by climate change are bound to force changes in resource supply to fuel primary productivity. Biological nitrogen fixation provides the largest source of reactive nitrogen in oligotrophic regions and responds positively to experimental temperature and CO₂ increases expected towards the end of the 21^st century.

A comparison of the two last generations of Earth system models indicates that the parametrisation of nitrogen fixation has a profound impact in net primary productivity predictions towards the end of the 21^st century. Among the global ocean regions, this increased global uncertainty is significantly driven by the Indian Ocean. However, the Indian Ocean represents only ~1% of the nitrogen fixation data available to date. Hence, constraining nitrogen fixation in the Indian Ocean gyre is crucial to improve the predictability of net primary productivity and the future role of the ocean as a climate change regulator.

EXPAND will provide mechanistic and quantitative understanding on how nitrogen fixation changes with gyre expansion seasonally, and its impact on primary productivity and export. This information will provide precious data coverage in this severely undersampled region, feeding models for a better parametrisation of nitrogen fixation and improved predictability of biological productivity in the future ocean.

Area of study

Indian Ocean subtropical gyre (see Fig. 1).