The Arctic Ocean is highly susceptible to climate change as evidenced by rapid warming and the drastic loss of sea ice during summer. The consequences of these environmental changes for the microbial cycling of organic matter are largely unexplored. Here, we investigated the distribution and composition of dissolved organic matter (DOM) along with heterotrophic bacterial activity in seawater and sea ice of the Eurasian Basin at the time of the record ice minimum in 2012. Bacteria in seawater were highly responsive to fresh organic matter and remineralized on average 55% of primary production in the upper mixed layer. Correlation analysis showed that the accumulation of dissolved combined carbohydrates (DCCHO) and dissolved amino acids (DAA), two major components of fresh organic matter, was related to the drawdown of nitrate. Nitrate‐depleted surface waters at stations adjacent to the Laptev Sea showed about 25% higher concentrations of DAA than stations adjacent to the Barents Sea and in the central Arctic basin. Carbohydrate concentration was the best predictor of heterotrophic bacterial activity in sea ice. In contrast, variability in sea‐ice bacterial biomass was largely driven by differences in ice thickness. This decoupling of bacterial biomass and activity may mitigate the negative effects of biomass loss due to ice melting on heterotrophic bacterial functions. Overall, our results reveal that changes in DOM production and inventories induced by sea‐ice loss have a high potential to enhance the bacterial remineralization of organic matter in seawater and sea ice of the Arctic Ocean.

中文翻译：

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北冰洋中部夏季海冰减少的有机质组成和异养细菌活动

北冰洋极易受到气候变化的影响，夏季迅速变暖和海冰急剧减少就证明了这一点。这些环境变化对有机物质微生物循环的影响在很大程度上尚未得到探索。在这里，我们调查了 2012 年冰量最低时欧亚盆地海水和海冰中溶解有机物 (DOM) 的分布和组成以及异养细菌活动。海水中的细菌对新鲜有机物高度敏感上混合层中平均 55% 的初级产品再矿化。相关性分析表明，溶解结合碳水化合物（DCCHO）和溶解氨基酸（DAA）这两个新鲜有机物质的主要成分的积累与硝酸盐的下降有关。与靠近巴伦支海和北极中部盆地的站点相比，拉普捷夫海附近站点的贫硝酸盐地表水的 DAA 浓度高出约 25%。碳水化合物浓度是海冰中异养细菌活动的最佳预测指标。相比之下，海冰细菌生物量的变化主要是由冰厚度的差异驱动的。细菌生物量和活性的这种脱钩可以减轻由于冰融化对异养细菌功能造成的生物量损失的负面影响。总体而言，我们的研究结果表明，海冰损失引起的 DOM 生产和库存变化具有很大的潜力，可以增强北冰洋海水和海冰中有机物的细菌再矿化。