Global reconstruction reduces the uncertainty of oceanic nitrous oxide emissions and reveals a vigorous seasonal cycle
Global reconstruction reduces the uncertainty of oceanic nitrous oxide emissions and reveals a vigorous seasonal cycle
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DOI：
10.1073/pnas.1921914117
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发表时间：
2020-05
期刊：
影响因子：
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通讯作者：
Simon Yang;B. Chang;M. Warner;T. Weber;A. Bourbonnais;A. Santoro;A. Kock;R. Sonnerup;J. L. Bull
中科院分区：
文献类型：
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作者：
Simon Yang;B. Chang;M. Warner;T. Weber;A. Bourbonnais;A. Santoro;A. Kock;R. Sonnerup;J. L. Bull
重要性N2 O是一种强有力的温室气体，其海洋排放仍然没有得到很好的限制。在这里，我们从迄今为止最大的观测合成中重建了海洋N2 O排放量，与以前的估计相比，大大降低了不确定性，并使这种气体的全球预算更加紧张。我们还揭示了一个充满活力的全球季节性循环，主要是生产，低氧热带地区，这表明N2 O循环的自然气候变率和人为气候变化的敏感性。由于对海洋N2 O向大气的通量知之甚少，对温室气体一氧化二氮（N2 O）的全球收支的评估受到限制，海洋N2 O通量的大小、空间分布和时间变化仍然高度不确定。在这里，我们通过训练一个监督学习算法来重建海洋的气候学N2 O排放，该算法使用了来自海洋表面的158，000多个N2 O测量值-这是迄今为止最大的合成。重建捕获观测到的纬度梯度和沿海热点的N2 O通量，并揭示了一个充满活力的全球季节循环。我们估计年平均N2 O通量为4.2 ± 1.0 Tg N y−1，其中64%发生在热带，20%发生在占海洋面积不到3%的沿海上升流系统。N2 O通量的范围从春季的3.3 ± 1.3 Tg N y−1到夏季的5.5 ± 2.0 Tg N y−1。全球N2 O排放的季节性变化大部分可追溯到热带海洋的季节性上升流和南大洋的冬季混合。生产性的，低氧的热带上升流系统（>75%）的季节性的主要贡献表明全球N2 O通量的敏感性厄尔尼诺-南方涛动和低纬度海洋的人为分层。这一海洋通量估计值与政府间气候变化专门委员会采用的范围一致，但将其不确定性降低了五倍以上，从而能够更精确地确定大气N2 O预算中的其他条款。
Significance N2O is a potent greenhouse gas whose oceanic emissions are still poorly constrained. Here, we reconstruct oceanic N2O emissions from the largest observational synthesis to date, substantially reducing the uncertainty compared to previous estimates and enabling a tightening of the global budget of this gas. We also reveal a vigorous global seasonal cycle, dominated by productive, low-oxygen tropical regions, which suggests sensitivity of the N2O cycle to natural climate variability and anthropogenic climate change. Assessment of the global budget of the greenhouse gas nitrous oxide (N2O) is limited by poor knowledge of the oceanic N2O flux to the atmosphere, of which the magnitude, spatial distribution, and temporal variability remain highly uncertain. Here, we reconstruct climatological N2O emissions from the ocean by training a supervised learning algorithm with over 158,000 N2O measurements from the surface ocean—the largest synthesis to date. The reconstruction captures observed latitudinal gradients and coastal hot spots of N2O flux and reveals a vigorous global seasonal cycle. We estimate an annual mean N2O flux of 4.2 ± 1.0 Tg N⋅y−1, 64% of which occurs in the tropics, and 20% in coastal upwelling systems that occupy less than 3% of the ocean area. This N2O flux ranges from a low of 3.3 ± 1.3 Tg N⋅y−1 in the boreal spring to a high of 5.5 ± 2.0 Tg N⋅y−1 in the boreal summer. Much of the seasonal variations in global N2O emissions can be traced to seasonal upwelling in the tropical ocean and winter mixing in the Southern Ocean. The dominant contribution to seasonality by productive, low-oxygen tropical upwelling systems (>75%) suggests a sensitivity of the global N2O flux to El Niño–Southern Oscillation and anthropogenic stratification of the low latitude ocean. This ocean flux estimate is consistent with the range adopted by the Intergovernmental Panel on Climate Change, but reduces its uncertainty by more than fivefold, enabling more precise determination of other terms in the atmospheric N2O budget.