1338 / 2024-09-24 08:33:43

Nitrous oxide production in expanding oxygen minimum zones

nitrous oxide,oxygen minimum zones,Ocean deoxygenation

Session 15 - Ocean deoxygenation: drivers, trends, and biogeochemical-ecosystem impacts

Oxygen minimum zones are a major source of nitrous oxide (N2O), a potent greenhouse gas. Net N2O accumulation reflects a balance between nitrification in oxygenated waters and both production and consumption by denitrification in low-oxygen and anoxic waters. However, the exact sensitivity of net N2O production to environmental gradients and future changes remains uncertain. Here, we combine a global reconstruction of oceanic N2O distribution with an ocean circulation inverse model to infer patterns of N2O production and consumption. Our results show N2O consumption below oxygen concentrations of 5 mmol/m3, peak production around 20 mmol/m3, and a gradual decline in production as oxygen levels rise. The reconstructed N2O source from aerobic remineralization exceeds nitrification yields from field measurements, suggesting eddy amplification at oxygen minimum zone boundaries and particle-bound denitrification in low-oxygen, non-anoxic waters. N2O production is projected to increase with expanding low-oxygen waters and shrinking anoxic zones, but this is partially offset by reduced organic matter export in a more stratified low-latitude ocean.