Equatorial upwelling enhances nitrogen fixation in the Atlantic Ocean
Equatorial upwelling enhances nitrogen fixation in the Atlantic Ocean
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DOI：
10.1002/grl.50250
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发表时间：
2013-05
影响因子：
5.2
通讯作者：
A. Subramaniam;C. Mahaffey;W. Johns;N. Mahowald
中科院分区：
文献类型：
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作者：
A. Subramaniam;C. Mahaffey;W. Johns;N. Mahowald
上升流区的表层沃茨被认为是营养丰富的，因此抑制固氮（固氮），因为固氮生物可以优先同化硝酸盐和氨，而不是消耗能量来固定二氮。我们发现，在赤道东大西洋的上升流区域的表面沃茨中，平均固氮率比在非上升流期间通常测量的要高2到7倍。我们认为，在这一地区，低硝酸盐-磷酸盐比例的沃茨是上升的，和非固氮浮游植物的初始水华删除最近上升的硝酸盐。因此，固氮是由残留的磷酸盐和风成和涌上的铁源的组合。每年，我们估计，约47 Gmol的新氮是由固氮引进单独的涌上沃茨和195 Gmol N是固定在赤道大西洋地区。我们的研究结果挑战了最高固氮率发生在贫营养环流中的范式，而是提供了其在上涌制度中的重要性的证据，其中富含磷酸盐和铁的沃茨丰富的上涌。
Surface waters in upwelling regions are thought to be nutrient rich and hence inhibit nitrogen fixation (diazotrophy) because diazotrophs can preferentially assimilate nitrate and ammonia instead of expending energy to fix dinitrogen. We found average nitrogen fixation rates to be two to seven times higher in the surface waters of the upwelling region of the eastern equatorial Atlantic than typically measured here during non‐upwelling periods. We posit that in this region, low nitrate‐phosphate ratio waters are upwelled, and an initial bloom of non‐diazotrophic phytoplankton removes recently upwelled nitrate. Thereby, diazotrophy is fuelled by residual phosphate and by a combination of aeolian and upwelled sources of iron. Annually, we estimate that approximately 47 Gmol of new nitrogen is introduced by diazotrophy in upwelled waters alone and 195 Gmol N is fixed in the equatorial Atlantic region. Our findings challenge the paradigm that the highest nitrogen fixation rates occur in oligotrophic gyres and instead provide evidence of its importance in upwelling regimes where phosphate‐ and iron‐rich waters rich are upwelled.