Nitric oxide supersaturation in the surface waters of the oligotrophic Atlantic Ocean

Atmospheric nitric oxide (NO) is a pollutant and climate-relevant trace gas. Dissolved NO accumulates in the surface ocean and therefore the ocean is a natural source of atmospheric NO. It is generally assumed that NO in the surface ocean is produced photochemically from nitrite (NO₂⁻). Here, we present the first dissolved NO measurements in the oligotrophic North Atlantic Ocean during an east-to-west transect (December 2021/January 2022). NO concentrations and mean saturations ranged from 9.4 to 48.2 pM and 10,355% to 19,484%, respectively, indicating that the study site was indeed a significant source of atmospheric NO despite extremely low NO₂⁻ concentrations. NO concentrations correlated significantly with phytoplankton pigment concentrations, indicating that NO variability may be influenced by phytoplankton-related processes rather than photochemical pathways alone. These findings highlight the need to further investigate the production mechanism of NO in nutrient-poor oceanic environments.