We report on the spatial distributions and optical characteristics of chromophoric dissolved organic matter (CDOM) in the sea surface microlayer (SML), subsurface seawater (SSW), and water column profiles down to 500 m across a range of Atlantic Ocean biogeochemical provinces during two cruises of the UK Atlantic Meridional Transect program (AMT24 and AMT25). We measured the CDOM absorption coefficient at 300 nm, aCDOM(300), and determined CDOM spectral slopes across two UV wavelength ranges: S1 (275-295 nm) and S2 (350-400 nm). We used spectral slope ratios (SR: S1/S2) to infer CDOM source characteristics and transformation history. During both cruises, SML aCDOM(300) was highest in the Northern Hemisphere, particularly in the North Atlantic Drift Region (NADR). CDOM was always enriched in the SML, with enrichment factors (SML aCDOM(300) / SSW aCDOM(300)) ranging from 1.03 to 2.00, reflecting preferential accumulation of CDOM in the SML. We also found a significant inverse correlation between aCDOM(300) and S1 in both the SML (Spearman’s rank correlation coefficient, r2 = -0.75, p < 0.001, n = 114) and water column profiles (r2 = -0.74, p < 0.001, n = 845). Biogeochemical province-dependent variations in the relationships between CDOM and chlorophyll a were also observed. In high-latitude regions, elevated aCDOM(300) and low SR values indicated a dominance of terrestrially-derived CDOM, whereas oligotrophic subtropical areas showed lower aCDOM(300) and higher SR values, suggestive of aged, refractory, and photodegraded biologically-derived CDOM. Taken together, these findings reveal a complexity of drivers affecting CDOM distributions and spectral properties, which may limit the use of CDOM in predictive relationships in the oceans. However, the potential use of chlorophyll a as a CDOM proxy may prove most successful in open ocean regions devoid of terrestrial inputs, where biological production predominates.

中文翻译：

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“大西洋中发色溶解有机物的动力学：揭示省份依赖性关系、光学复杂性和环境影响”


我们报告了两个时期大西洋一系列生物地球化学区海面微层 (SML)、地下海水 (SSW) 和深至 500 m 的水柱剖面中发色溶解有机物 (CDOM) 的空间分布和光学特征。英国大西洋经线断面计划（AMT24 和 AMT25）的巡航。我们测量了 300 nm 处的 CDOM 吸收系数 aCDOM(300)，并确定了两个 UV 波长范围内的 CDOM 光谱斜率：S1 (275-295 nm) 和 S2 (350-400 nm)。我们使用光谱斜率（SR：S1/S2）来推断 CDOM 源特征和转换历史。在两次航行期间，SML aCDOM(300) 在北半球最高，特别是在北大西洋漂移区 (NADR)。 CDOM始终在SML中富集，富集因子（SML aCDOM（300）/SSW aCDOM（300））范围为1.03至2.00，反映了CDOM在SML中的优先积累。我们还在 SML（斯皮尔曼等级相关系数，r2 = -0.75，p < 0.001，n = 114）和水柱剖面（r2 = -0.74，p < 0.001）中发现 aCDOM（300）和 S1 之间存在显着的负相关，n = 845）。还观察到 CDOM 和叶绿素 a 之间关系的生物地球化学省依赖性变化。在高纬度地区，较高的aCDOM（300）和较低的SR值表明陆地来源的CDOM占主导地位，而贫营养亚热带地区则表现出较低的aCDOM（300）和较高的SR值，表明老化、难治和光降解的生物来源CDOM。总而言之，这些发现揭示了影响 CDOM 分布和光谱特性的驱动因素的复杂性，这可能会限制 CDOM 在海洋预测关系中的使用。 然而，叶绿素 a 作为 CDOM 替代物的潜在用途可能在缺乏陆地输入、生物生产占主导地位的公海区域最为成功。