Climate change models predict increasing uncertainty in biological productivity by the end of the 21st century, especially in the Indian Ocean (IO), which currently holds just 1% of the global nitrogen fixation data. While much of the existing knowledge about nitrogen fixation (N2) is based on "bottom-up" factors such as temperature and nutrients, emerging research suggests that "top-down" factors, including grazing and species interactions, may also significantly impact nitrogen fixation. However, these dynamics have yet to be studied in the Indian Ocean, one of the least explored regions in oceanographic research.

This PhD project, part of the ERC-funded EXPAND project, provides a unique opportunity to investigate the role of top-down controls on nitrogen fixation in the IO gyre. The selected candidate will participate in two oceanographic expeditions aboard the Research Vessel Marion Dufresne, exploring both the minimum and maximum seasonal expansions of the Indian Ocean gyre. The candidate will employ state-of-the-art techniques such as nanoscale secondary ion mass spectrometry (nanoSIMS) at the IOW (Germany) and advanced genetic and bioinformatic analyses at the University of Southampton (UK) to study the impact of grazing and species interactions on nitrogen fixation.

Key project aspects include:

• Measuring top-down controls on N2 fixation during at-sea experiments
• Bridging the gap between ocean desert expansion and N2 fixation
• Multidisciplinary training in microbiology, oceanography, mass spectrometry, molecular and bioinformatic techniques

The successful candidate will receive hands-on experience in oceanographic cruises, experimental design for nitrogen fixation measurements, stable isotope tracing, molecular sampling, omics analyses, flow cytometry, and nanoSIMS.