The marine N cycle is driven mainly by microorganisms whose distribution can be shaped by mesoscale eddies. Recently, eddies containing oxygen minimum zones (OMZs) have been recognised as N-loss hotspots, complicating even more the calculations of the marine N budgets. As a contribution to this understanding, we investigated the effect of a cyclonic eddy confined in an oxygen-depleted basin on the distribution of the N-cycling communities. We measured hydrographic properties of the water column, nutrient concentrations, and the abundance of key genes involved in the processes of nitrification (archaeal and bacterial amoA), denitrification (nirS and nirK), dissimilatory nitrate reduction to ammonia (DNRA; nrfA) and anammox (hzo) within the eddy. Our results indicated that the cyclonic circulation affected the distribution of nutrients and the abundance of amoA and nirS genes, whereas oxygen influenced the distribution of nirK, nrfA, and hzo genes. Additionally, the aerobic ammonium oxidation by archaea seems to be an important source of nitrite, which might fuel denitrifier, DNRA, and anammox communities in this basin. These findings along with the high N deficit in the OMZ suggest the existence of an active N cycling that might enhance the N-loss in this oxygen-depleted basin.

海洋氮循环主要是由微生物驱动的，这些微生物的分布可以由中等规模的涡旋形成。最近，包含氧气最小区域（OMZ）的涡流已被认为是N损失热点，这使海洋N预算的计算更加复杂。为了促进这种理解，我们研究了在缺氧的盆地中局限的旋风涡流对N循环群落分布的影响。我们测量了水柱的水文特性，养分浓度以及涉及硝化作用（古细菌和细菌amo A），反硝化作用（nir S和nir K），异化硝酸盐还原为氨水（DNRA; nrf）的关键基因的丰度A）和厌氧氨水（hzo）在涡流中。我们的结果表明，气旋循环影响营养物的分布以及amo A和nir S基因的丰度，而氧气影响nir K，nrf A和hzo基因的分布。此外，古细菌的需氧铵氧化似乎是亚硝酸盐的重要来源，可能为该盆地的反硝化，DNRA和厌氧氨氮群落提供燃料。这些发现以及OMZ中的高N亏缺表明存在活跃的N循环，这可能会增加该缺氧盆地中N的损失。