The Eastern South Pacific coastal zone is characterized by seasonal and interannual variability, driven by upwelling and El Niño Southern Oscillation (ENSO), respectively. These oceanographical conditions influence microbial communities and their contribution to nutrient and greenhouse gases recycling, especially in bottom waters due to oxygenation. This article addresses the seasonal hydrographic and biogeochemical conditions in the water and sediments during El Niño 2015. Bottom water active microbial communities, including nitrifiers, were studied using amplicon sequencing of 16S rRNA (cDNA) and RT-qPCR, respectively. The results of the hydrographic analysis showed changes in the water column associated with the predominance of sub-Antarctic Waters characterized by warmed and low nutrients in the surface and more oxygenated conditions at the bottom in comparison with El Niño 2014. The organic matter quantity and quality decreased during fall and winter. The bottom water active microbial assemblages were dominated by archaea (Ca. Poseidoniales) and putative ammonia oxidizing archaea. Active bacteria affiliated to SAR11, Marinimicrobia and Nitrospina, and oxygen deficient realms (Desulfobacterales, SUP05 clade and anammox) suffered variations, possibly associated with oxygen and redox conditions in the benthic boundary layer. Nitrifying functional groups contributed significantly more during late fall and winter which was consistent with higher bottom water oxygenation. Relationships between apparent oxygen utilization nitrate and nitrous oxide in the water support the contribution of nitrification to this greenhouse gas distribution in the water. In general, our study suggests that seasonal oceanographic variability during an El Niño year influences the microbial community and thus remineralization potential, which supports the need to carry out longer time series to identify the relevance of seasonality under ENSO in Eastern Boundary Upwelling Systems (EBUS) areas.

中文翻译：

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2015年厄尔尼诺事件期间东部边界上升系统中底栖边界层微生物群落的生物地球化学响应和季节动态

南太平洋东部沿海地区的特征是季节变化和年际变化，分别由上升流和厄尔尼诺南方涛动（ENSO）驱动。这些海洋条件会影响微生物群落及其对养分和温室气体再循环的贡献，尤其是在由于氧合作用而导致的底水中。本文介绍了2015年厄尔尼诺现象期间水和沉积物的季节性水文和生物地球化学条件。分别使用16S rRNA（cDNA）和RT-qPCR的扩增子测序研究了包括硝化剂在内的底水活性微生物群落。水文分析的结果表明，与厄尔尼诺（ElNiño）2014年相比，南极亚水域的水柱变化主要表现为地表温度低，营养少，底部含氧量高等特点。有机质的数量和质量在秋季和冬季减少。底水活性微生物组合以古细菌为主（钙Poseidoniales）和推定的氨氧化古细菌。隶属于SAR11，Marinimicrobia和Nitrospina的活性细菌以及缺氧领域（脱硫细菌，SUP05进化枝和厌氧氨氧化菌）遭受变异，可能与底栖边界层的氧气和氧化还原条件有关。硝化官能团在深秋和冬季的贡献更大，这与较高的底部水氧合相一致。水中的表观氧气利用率硝酸盐和一氧化二氮之间的关系支持了硝化作用对水中温室气体分布的贡献。总体而言，我们的研究表明，厄尔尼诺现象期间的季节性海洋变化会影响微生物群落，从而影响再矿化的潜力，