Phytoplankton blooms can be an important source of autochthonous chromophoric dissolved organic matter (CDOM) in surface oceans. Here we report the first detection and optical characterization of CDOM produced during a Dictyocha fibula bloom occurring in the western central Bohai Sea in mid-summer 2019. The mean CDOM absorption coefficient at 330 nm (a_CDOM(330)) in the surface water of the bloom area (3.16 ± 0.48 m⁻¹) was 2.5 times higher than that of the adjacent bloom-absent area (1.26 ± 0.34 m⁻¹). The a_CDOM(330) increased exponentially to a maximum with increasing chlorophyll a and cell abundance of D. fibula, indicating a steady state was reached between production and consumption of CDOM. The biological index (BIX) of the fluorescent DOM (FDOM) showed little variation between bloom and background areas. The combination of these observations points to an extensive production of autochthonous CDOM by D. fibula in the bloom area. Mass budgeting indicates that the net production of CDOM by D. fibula (a_CDOM(330): 1.98 ± 0.48 m⁻¹) accounted for 63% of the total net accumulation of CDOM in the bloom area (a_CDOM(330): 3.16 ± 0.48 m⁻¹) since the onset of the bloom event. The spectral slope coefficients over 275–295 nm (S_275–295) in the bloom area (range: 0.0228–0.0241 nm⁻¹; mean: 0.0235 nm⁻¹) were substantially lower than those in the bloom-absent area (range: 0.0240–0.0311 nm⁻¹; mean: 0.0271 nm⁻¹), suggesting a high-molecular-weight nature of the D. fibula-derived CDOM. The freshly produced CDOM contained two humic-like FDOM components and one protein-like FDOM component, and the three FDOM components were depleted in fresh CDOM relative to their counterparts in CDOM within the background area. Owing to the episodic nature of algal bloom-driven CDOM production, future attention should be paid to accelerated biogeochemical cycles (e.g., spiked oceanic trace gas emission) associated with CDOM photochemistry during algal blooms which can be easily missed for pre-scheduled field surveys.

浮游植物大量繁殖可能是表层海洋中本土发色溶解有机物 (CDOM) 的重要来源。在这里，我们报告了2019 年仲夏渤海中西部发生的腓骨盘藻水华期间产生的 CDOM 的首次检测和光学表征。在 330 nm 处的平均 CDOM 吸收系数 ( a _CDOM (330)) 在地表水中绽放区域（3.16 ± 0.48 m ^-1）比相邻的没有绽放区域（1.26 ± 0.34 m ^-1）高2.5倍。随着叶绿素a和D. fibula细胞丰度的增加，a _{CDOM (330) 呈指数增加至最大值}, 表明 CDOM 的生产和消费之间达到了稳定状态。荧光 DOM (FDOM) 的生物指数 (BIX) 在绽放区域和背景区域之间几乎没有变化。这些观察结果的结合表明D. fibula在开花区大量生产了本土 CDOM。质量预算表明D. fibula的 CDOM 净产量（a _CDOM (330): 1.98 ± 0.48 m ^-1）占开花区 CDOM 总净积累量的 63%（a _CDOM (330): 3.16） ± 0.48 m ^-1 ) 自开花事件开始以来。光谱斜率系数超过 275–295 nm ( S _275–295) 在开花区（范围：0.0228–0.0241 nm ^-1；平均值：0.0235 nm ^-1）明显低于没有开花区（范围：0.0240–0.0311 nm ^-1；平均值：0.0271 nm ^-1） ，表明D. fibula的高分子量性质-派生的CDOM。新鲜生产的 CDOM 含有两种类腐殖质 FDOM 成分和一种类蛋白质 FDOM 成分，并且三种 FDOM 成分在新鲜 CDOM 中相对于它们在背景区域内的 CDOM 对应物被耗尽。由于藻华驱动的 CDOM 产生的偶发性，未来应关注与藻华期间 CDOM 光化学相关的加速生物地球化学循环（例如，海洋微量气体排放的尖峰），这对于预先安排的实地调查很容易错过。