Fronts divide diazotroph communities in the Southern Indian Ocean

• DOI: 10.1093/femsec/fiae095
• Publication Date: 2024-07-10T20:30:10Z
• Authors: Subhadeep Chowdhury; Hugo Berthelot; Corentin Baudet; David González-Sa...; Christian Furbo R...; Stéphane L'Helguen; Jean-François Maguer; Carolin R Löscher; Arvind Singh; Stéphane Blain; Nicolas Cassar; Sophie Bonnet; Hélène Planquette; Mar Benavides
• Keywords: N 2 fixation; 0303 health sciences; 550; trace metals; noncyanobacterial diazotrophs; Noncyanobacterial diazotrophs; 03 medical and health sciences; Hnlc; fronts; N-2 fixation; Trace metals; HNLC; [SDE]Environmental Sciences; 251001 Oceanografía biológica; Fronts; subtropical gyre; N fixation; Subtropical gyre; fronts HNLC N 2 fixation noncyanobacterial diazotrophs subtropical gyre trace metals; Research Article

AbstractDinitrogen (N2) fixation represents a key source of reactive nitrogen in marine ecosystems. While the process has been rather well-explored in low latitudes of the Atlantic and Pacific Oceans, other higher latitude regions and particularly the Indian Ocean have been chronically overlooked. Here, we characterize N2 fixation and diazotroph community composition across nutrient and trace metals gradients spanning the multifrontal system separating the oligotrophic waters of the Indian Ocean subtropical gyre from the high nutrient low chlorophyll waters of the Southern Ocean. We found a sharp contrasting distribution of diazotroph groups across the frontal system. Notably, cyanobacterial diazotrophs dominated north of fronts, driving high N2 fixation rates (up to 13.96 nmol N l−1 d−1) with notable peaks near the South African coast. South of the fronts non-cyanobacterial diazotrophs prevailed without significant N2 fixation activity being detected. Our results provide new crucial insights into high latitude diazotrophy in the Indian Ocean, which should contribute to improved climate model parameterization and enhanced constraints on global net primary productivity projections.