Arctic rivers are sensitive to climate and environmental change, but the biogeochemical response remains poorly understood. Monthly size-fractionated dissolved organic matter (DOM) samples from the lower Yukon River were characterized using UV–visible, fluorescence, and Fourier transform-infrared (FT-IR) spectroscopy techniques. The EEM-PARAFAC analysis revealed three major fluorescent DOM components, including two humic-like components (C₄₈₀ and C₄₀₀) and one protein-like component (C₃₁₀), with their relative importance following the order of C₄₈₀ ≥ C₄₀₀ > C₃₁₀ in the high-molecular-weight DOM (1 kDa–0.4 μm) and C₄₀₀ > C₄₈₀ > C₃₁₀ in the low-molecular-weight DOM pool (< 1 kDa). Transformation in DOM and change in sources were manifested in major fluorescent components and optical properties, including biological index (BIX), humification index (HIX), spectral slope (S_275–295) and specific UV absorbance at 254 nm (SUVA₂₅₄). These changes occurred within different DOM size-fractions and among ice-covered, spring freshet, and open seasons. Joint analysis of EEM and FT-IR spectra using a data fusion technique showed that humic-like DOM is mostly associated with C─H, C═C, and C─O bonds, while protein-like DOM is correlated more with C─N and N─H related structures. DOM aromaticity and the ratios of HIX to BIX and protein-like to humic-like components may be used as a compelling proxy to measure change in source waters and to infer permafrost dynamics. Our results provide insight into the seasonal variation in DOM composition for different size-fractions in the lower Yukon River, and a baseline dataset against which future changes can be understood in the context of arctic basin biogeochemical cycling.

中文翻译：

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季节性冰层覆盖的北极河流中粒度分馏溶解有机物组成的动态变化

北极河流对气候和环境变化很敏感，但对其生物地球化学反应知之甚少。使用紫外-可见光、荧光和傅里叶变换红外 (FT-IR) 光谱技术对来自育空河下游的每月粒度分级溶解有机物 (DOM) 样品进行了表征。EEM-PARAFAC 分析揭示了三种主要的荧光 DOM 组分，包括两种类腐殖质组分（C ₄₈₀和 C ₄₀₀）和一种类蛋白质组分（C ₃₁₀），它们的相对重要性遵循 C ₄₈₀  ≥ C ₄₀₀  > ç ₃₁₀在高分子量DOM（1 kDa的-0.4  μ M）和C ₄₀₀  >ç低分子量 DOM 池中的₄₈₀  > C ₃₁₀ (< 1 kDa)。DOM 的转变和来源的变化体现在主要的荧光成分和光学特性上，包括生物指数 (BIX)、腐殖化指数 (HIX)、光谱斜率 ( S _275–295 ) 和 254 nm 处的比紫外吸光度 (SUVA ₂₅₄₎）。这些变化发生在不同的 DOM 大小部分以及冰覆盖、春季新鲜和开放季节之间。使用数据融合技术对 EEM 和 FT-IR 光谱的联合分析表明，类腐殖质 DOM 主要与 C─H、C=C 和 C─O 键相关，而类蛋白质 DOM 与 C─N 相关性更高和 N─H 相关结构。DOM 芳香性和 HIX 与 BIX 的比率以及类蛋白质与类腐殖质组分的比率可用作衡量源水变化和推断永久冻土动态的引人注目的代理。我们的结果提供了对育空河下游不同尺寸部分 DOM 组成的季节性变化的洞察，以及一个基线数据集，可以在北极盆地生物地球化学循环的背景下了解未来的变化。