The removal of carbon dioxide from the atmosphere by the marine biological pump is a key regulator of Earth’s climate; however, the ocean also serves as a large source of nitrous oxide, a potent greenhouse gas and ozone-depleting substance. Although biological carbon sequestration and nitrous oxide production have been individually studied in the ocean, their combined impacts on net greenhouse forcing remain uncertain. Here we show that the magnitude of nitrous oxide production in the epipelagic zone of the subtropical ocean covaries with remineralization processes and thus acts antagonistically to weaken the radiative benefit of carbon removal by the marine biological pump. Carbon and nitrogen isotope tracer incubation experiments and nitrogen isotope natural abundance data indicate enhanced biological activity promotes nitrogen recycling, leading to substantial nitrous oxide production via both oxidative and reductive pathways. These shallow-water nitrous oxide sources account for nearly half of the air–sea flux and counteract 6–27% (median 9%) of the greenhouse warming mitigation achieved by carbon export via the biological pump.

海洋生物泵从大气中去除二氧化碳是调节地球气候的关键；然而，海洋也是一氧化二氮、一种强效温室气体和消耗臭氧层物质的大量来源。尽管已经在海洋中分别研究了生物碳封存和一氧化二氮的产生，但它们对净温室效应的综合影响仍不确定。在这里，我们表明亚热带海洋表层带的一氧化二氮产生量与再矿化过程相关，因此起到对抗作用，削弱海洋生物泵去除碳的辐射效益。碳氮同位素示踪孵化实验和氮同位素自然丰度数据表明生物活性增强促进氮循环，通过氧化和还原途径导致大量一氧化二氮的产生。这些浅水一氧化二氮来源占空气-海洋通量的近一半，抵消了通过生物泵输出碳实现的 6-27%（中位数 9%）的温室效应减缓。