Absract: Dissolved black carbon (DBC) can be transported from land to the ocean, representing a significant slow-cycling component in the global carbon cycle. However, the source, distribution, and degradation of DBC in the ocean are not well understood. In this study, water samples were collected from the East China Sea (ECS) shelf to the Northwest Pacific Ocean. The benzene polycarboxylic acid (BPCA) method and ultraviolet–visible spectroscopy were used to analyze DBC and dissolved organic matter, respectively. The concentration of DBC and the (B6CA + B5CA)/BPCAs ratio in surface water showed a decreasing trend from the ECS inner shelf towards the open ocean. This trend indicates the preferential removal of condensed aromatic compounds by photodegradation, while also implicating dilution by open ocean water as a significant factor contributing to the reduction of DBC concentrations. A significant negative correlation between DBC concentration and salinity was observed in surface water samples (r = − 0.88; p < 0.01). However, this relationship weakened and disappeared in offshore samples, suggesting a reduced influence of riverine inputs. Furthermore, vertical profiles of water samples (0 – 1000 m) revealed a decrease in DBC concentrations and an increase in the ratio of (B6CA + B5CA)/BPCAs, indicating the preferential photodegradation of condensed aromatic DBC molecules in the euphotic zone and the selective accumulation of these molecules in the ocean interior. The DBC flux into the Northwest Pacific Ocean was estimated to be 1.46 Tg/year with 51.7 to 73.1 % removed through photodegradation, while the remaining DBC was either transported into the deep ocean or biodegraded. Given the important role of photodegradation in regulating the DBC flux in the Northwest Pacific Ocean, we recommend further research into its impact on the refractory carbon cycle in global oceans.

中文翻译：

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从东海大陆架到西北太平洋公海溶解黑碳的非均相来源、分布和去除过程


吸收：溶解的黑碳 （DBC） 可以从陆地运输到海洋，是全球碳循环中重要的慢循环组成部分。然而，DBC 在海洋中的来源、分布和降解尚不清楚。在这项研究中，从东海 （ECS） 大陆架收集了到西北太平洋的水样。苯聚羧酸 （BPCA） 法和紫外-可见光谱法分别用于分析 DBC 和溶解有机物。表层水中 DBC 浓度和 （B6CA + B5CA）/BPCAs 比率从 ECS 内陆架向开阔海洋呈下降趋势。这一趋势表明，通过光降解优先去除缩合芳香族化合物，同时也意味着开阔海水的稀释是导致 DBC 浓度降低的重要因素。在地表水样品中观察到 DBC 浓度和盐度之间呈显著负相关 （r = − 0.88;p < 0.01）。然而，这种关系在海上样本中减弱并消失，表明河流输入的影响减弱。此外，水样 （0 – 1000 m） 的垂直剖面显示 DBC 浓度降低，（B6CA + B5CA）/BPCA 比率增加，表明浓缩芳香族 DBC 分子在真光区优先光降解，并且这些分子在海洋内部选择性积累。流入西北太平洋的 DBC 通量估计为 1.46 Tg/年，其中 51.7% 至 73.1% 通过光降解去除，而剩余的 DBC 要么被输送到深海中，要么被生物降解。 鉴于光降解在调节西北太平洋 DBC 通量中的重要作用，我们建议进一步研究其对全球海洋难降解碳循环的影响。