Imprint of Indian Ocean Dipole on nitrous oxide dynamics

The northern Indian Ocean is a hotspot of nitrous oxide (N₂O) emissions, with strong seasonal monsoons and interannual Indian Ocean Dipole (IOD) variability. We examine the IOD influence on N₂O seasonality using a regional ocean model covering 1981–2020, with a focus on the coastal ocean where ∆pN₂O variability is more than threefold greater than in the open ocean. Positive IOD amplifies ∆pN₂O seasonality by a factor 2 to 5 in the east and dampens it by ∼ 30% in the west. Negative IOD reverses this pattern but changes are weaker (< 10%). This east/west contrast and asymmetry between positive and negative IOD arise from changes in transport of N₂O produced in subsurface by nitrification and denitrification, and significantly modulate local N₂O emissions (−40% to +130%). Sparse N₂O observations and systematic biases in IOD phase sampling compound seasonal and interannual variability, likely leading to underestimation of N₂O seasonality and emissions in observation-based reconstructions.