EXPAND

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 21st 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 21st 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.

The EXPAND project (“will nitrogEn fiXation offset nitrogen dePletion in expAnding oceaN Deserts?”) aims to provide a mechanistic and quantitative understanding of how nitrogen fixation responds to the seasonal expansion of ocean gyres and how this affects primary productivity and export. By delivering much-needed observations from one of the most severely undersampled regions of the ocean, EXPAND will supply critical data to improve the parameterisation of nitrogen fixation in models and enhance predictions of future biological productivity.

As global warming drives further gyre expansion, the ocean’s reliance on N₂ fixation as a primary nitrogen source is expected to increase, making EXPAND a priority for oceanographic and climate research. The project integrates physical oceanography, biogeochemistry, molecular biology, and data science to quantify the variability of nitrogen fixation associated with seasonal gyre expansion and to assess its impact on primary productivity and carbon sequestration. Ultimately, EXPAND seeks to resolve the full spatial extent and seasonal variability of gyre expansion, providing a holistic view of nitrogen fixation dynamics in the Indian Ocean desert.