Convergent estimates of marine nitrogen fixation
Convergent estimates of marine nitrogen fixation
复制标题
DOI：
10.1038/s41586-019-0911-2
复制
发表时间：
2019-02-14
期刊：
影响因子：
64.8
通讯作者：
Primeau, Francois W.
中科院分区：
文献类型：
--
作者：
Wang, Wei-Lei;Moore, J. Keith;Primeau, Francois W.
海洋固氮全球模式的不确定性限制了我们对海洋氮和碳循环对环境变化响应的理解。由于原位测量有限，固氮的地理分布和生态控制难以确定。在此，我们通过一个生物地球化学反演模型和一个预测性海洋模型给出了固氮的趋同估计。我们的结果表明，输出有机物的氮磷比存在很强的空间变异性，这极大地提高了全球固氮率（因为在磷供应短缺时，浮游植物可以用更少的磷维持生存）。我们发现，来自微生物固氮以及外部输入（大气沉降和河流通量）的新固定氮的输入，在亚热带环流中占碳输出的比例高达50%。我们还发现，固氮和反硝化在空间上是解耦的，但在过去几十年中，氮的源和汇似乎是平衡的。此外，我们提出了自上而下的浮游动物捕食控制在塑造全球固氮模式中的作用。我们的研究结果表明，海洋中的生物碳输出比预期的要高，而稳定氮循环的反馈比之前认为的要弱。
Uncertainty in the global patterns of marine nitrogen fixation limits our understanding of the response of the ocean's nitrogen and carbon cycles to environmental change. The geographical distribution of and ecological controls on nitrogen fixation are difficult to constrain with limited in situ measurements. Here we present convergent estimates of nitrogen fixation from an inverse biogeochemical and a prognostic ocean model. Our results demonstrate strong spatial variability in the nitrogen-to-phosphorus ratio of exported organic matter that greatly increases the global nitrogen-fixation rate (because phytoplankton manage with less phosphorus when it is in short supply). We find that the input of newly fixed nitrogen from microbial fixation and external inputs (atmospheric deposition and river fluxes) accounts for up to 50 per cent of carbon export in subtropical gyres. We also find that nitrogen fixation and denitrification are spatially decoupled but that nevertheless nitrogen sources and sinks appear to be balanced over the past few decades. Moreover, we propose a role for top-down zooplankton grazing control in shaping the global patterns of nitrogen fixation. Our findings suggest that biological carbon export in the ocean is higher than expected and that stabilizing nitrogen-cycle feedbacks are weaker than previously thought.