Shifts in the Isotopic Composition of Nitrous Oxide Between El Niño and La Niña in the Eastern Tropical South Pacific

IF 5.4 2区 地球科学 Q1 ENVIRONMENTAL SCIENCES Global Biogeochemical Cycles Pub Date : 2023-10-19 DOI:10.1029/2023GB007959
Noah Gluschankoff, Alyson E. Santoro, Carolyn Buchwald, Karen L. Casciotti
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Abstract

The El Niño-Southern Oscillation (ENSO) is a natural climate phenomenon that alters the biogeochemical and physical dynamics of the Eastern Tropical Pacific Ocean. Its two phases, El Niño and La Niña, are characterized by decreased and increased coastal upwelling, respectively, which have cascading effects on primary productivity, organic matter supply, and ocean-atmosphere interactions. The Eastern Tropical South Pacific oxygen minimum zone is a source of nitrous oxide (N2O), a potent greenhouse gas, to the atmosphere. Here, we present the first study to directly compare N2O sources during opposing ENSO phases using N2O isotopocule analyses. Our data show that during La Niña, N2O accumulation increased six-fold in the upper 100 m of the water column, and N2O fluxes to the atmosphere increased up to 20-fold. N2O isotopocule data demonstrated substantial increases in δ18O up to 60.5‰ and decreases in δ15Nβ down to −10.3‰ in the oxycline, signaling a shift in N2O cycling during La Niña compared to El Niño. During El Niño, N2O production was primarily due to ammonia-oxidizing archaea, whereas during La Niña, N2O production by incomplete denitrification supplemented that from ammonia-oxidation, with N2O consumption likely maintaining the high site preference values (up to 26.7‰). Ultimately, our results illustrate a strong connection between upwelling intensity, biogeochemistry, and N2O flux to the atmosphere. Additionally, they highlight the combined power of N2O isotopocule analysis and repeat measurements in the same region to constrain N2O interannual variability and cycling dynamics under different climate scenarios.

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热带南太平洋东部厄尔尼诺和拉尼娜之间一氧化二氮同位素组成的变化
厄尔尼诺-南方涛动(ENSO)是一种自然气候现象,它改变了东热带太平洋的生物地球化学和物理动力学。它的两个阶段,厄尔尼诺和拉尼娜,分别以海岸上升流减少和增加为特征,这对初级生产力、有机物供应和海洋-大气相互作用产生了级联效应。热带南太平洋东部的氧气最低区是大气中一氧化二氮(N2O)的来源,这是一种强效温室气体。在这里,我们首次使用N2O同位素分析直接比较ENSO相反阶段的N2O来源。我们的数据显示,在拉尼娜期间,水柱上部100米的N2O积累增加了6倍,向大气的N2O通量增加了20倍。N2O同位素数据显示,羟脯氨酸中δ18O显著增加至60.5‰,δ15Nβ显著减少至−10.3‰,这表明与厄尔尼诺相比,拉尼娜期间N2O循环发生了变化。在厄尔尼诺期间,N2O的产生主要是由于氨氧化古菌,而在拉尼娜期间,不完全反硝化产生的N2O补充了氨氧化产生的N2O,N2O消耗可能保持较高的位点偏好值(高达26.7‰)。最终,我们的结果表明,上升流强度、生物地球化学,以及N2O向大气的通量。此外,他们强调了N2O同位素分析和同一地区重复测量的综合能力,以约束不同气候情景下的N2O年际变化和循环动力学。
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来源期刊
Global Biogeochemical Cycles
Global Biogeochemical Cycles 环境科学-地球科学综合
CiteScore
8.90
自引率
7.70%
发文量
141
审稿时长
8-16 weeks
期刊介绍: Global Biogeochemical Cycles (GBC) features research on regional to global biogeochemical interactions, as well as more local studies that demonstrate fundamental implications for biogeochemical processing at regional or global scales. Published papers draw on a wide array of methods and knowledge and extend in time from the deep geologic past to recent historical and potential future interactions. This broad scope includes studies that elucidate human activities as interactive components of biogeochemical cycles and physical Earth Systems including climate. Authors are required to make their work accessible to a broad interdisciplinary range of scientists.
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