The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean
The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean
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DOI：
10.1038/s43247-022-00474-x
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发表时间：
2022-06
影响因子：
7.9
通讯作者：
Tanya A. Marshall;J. Granger;K. Casciotti;K. Dähnke;K. Emeis;D. Marconi;M. McIlvin;A. Noble;M. Saito;D. Sigman;S. Fawcett
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作者：
Tanya A. Marshall;J. Granger;K. Casciotti;K. Dähnke;K. Emeis;D. Marconi;M. McIlvin;A. Noble;M. Saito;D. Sigman;S. Fawcett
生物固氮是海洋系统新氮的主要来源，因此对海洋的生物泵是必不可少的。事实证明，限制固氮的分布和全球固氮率具有挑战性，这主要是由于围绕其控制的不确定性。现有的南大西洋氮固定速率估计值相差五倍，模型将大部分氮固定归因于西部盆地。从水文特征和硝酸盐同位素比值来看，热带南大西洋东部的安哥拉环流支持1.4Tg-5.4Tg N.A−1的固定，是现有(高度不确定的)估计的28%-108%。我们的观察与模型诊断相矛盾，揭示了新固定的氮大量输入到热带东部盆地，而在7.5˚W以西没有氮固定。我们提出，南大西洋的氮固定发生在热点地区，受边缘沉积物中过剩的磷与氮和生物有效铁的重叠生物地理控制。在类似的海洋区域，类似的条件可能会促进氮的固定。我们的分析表明，当地铁的可获得性导致磷驱动的海洋氮固定与氮损失的耦合在区域基础上有所不同。
Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the ocean’s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate estimates vary five-fold, with models attributing most dinitrogen fixation to the western basin. From hydrographic properties and nitrate isotope ratios, we show that the Angola Gyre in the eastern tropical South Atlantic supports the fixation of 1.4–5.4 Tg N.a−1, 28-108% of the existing (highly uncertain) estimates for the basin. Our observations contradict model diagnoses, revealing a substantial input of newly-fixed nitrogen to the tropical eastern basin and no dinitrogen fixation west of 7.5˚W. We propose that dinitrogen fixation in the South Atlantic occurs in hotspots controlled by the overlapping biogeography of excess phosphorus relative to nitrogen and bioavailable iron from margin sediments. Similar conditions may promote dinitrogen fixation in analogous ocean regions. Our analysis suggests that local iron availability causes the phosphorus-driven coupling of oceanic dinitrogen fixation to nitrogen loss to vary on a regional basis.