The marine biological pump removes atmospheric carbon dioxide, but the ocean also releases nitrous oxide (N2O), a potent greenhouse gas. This study shows that epipelagic N2O production, linked to remineralization processes, counteracts the climate benefits of carbon sequestration by the biological pump. Experiments and isotopic data indicate enhanced biological activity promotes nitrogen recycling, leading to significant N2O production via oxidative and reductive pathways. Shallow-water N2O sources account for nearly half of the air-sea flux, offsetting 6–27% (median 9%) of the carbon export's climate mitigation effect.

Xianhui S. Wan, Hua-Xia Sheng, Minhan Dai, Karen L. Casciotti, Matthew J. Church, Wenbin Zou, Li Liu, Hui Shen, Kuanbo Zhou, Bess B. Ward, Shuh-Ji Kao