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<p>Seawater samples collected from the continental shelf, continental slope, and Ulleung Basin were fractionated using 0.45&#xa0;μm, 0.2&#xa0;μm, 100&#xa0;kDa, and 1&#xa0;kDa cutoffs and analyzed for dissolved organic carbon (DOC) and fluorescence excitation-emission matrices to investigate the size-dependent distribution and behavior of colloidal dissolved organic matter (DOM) in the East Sea (Sea of Japan). The four-component Parallel Factor Analysis model resolved two protein-like components (C1, tyrosine-like; C2, tryptophan-like) and two humic-like components (C3, terrestrial humic-like; C4, marine humic-like). The protein-like components showed maxima at the subsurface chlorophyll maximum and were positively correlated with chlorophyll a (C1: r<sup>2</sup> = 0.66; C2: r<sup>2</sup> = 0.61), whereas humic-like components increased with apparent oxygen utilization (AOU; C3: r<sup>2</sup> = 0.55; C4: r<sup>2</sup> = 0.75). Size fractionation revealed that protein-like fluorescence was relatively enriched in the larger colloidal fractions, whereas humic-like fluorescence persisted strongly in the &lt; 100&#xa0;kDa and &lt; 1&#xa0;kDa pools. When operational size classes were defined using the 1&#xa0;kDa cutoff, the high-molecular-weight (HMW) DOC fraction decreased with AOU (r<sup>2</sup> = 0.90). In contrast, the low-molecular-weight (LMW) DOC remained nearly constant, indicating a preferential remineralization of larger and more reactive DOM during water-mass aging. Surface DOC was highest in low-salinity shelf-influenced water, suggesting lateral inputs from continental shelf waters and/or terrestrial sources. Together, these results show that the combined effects of source mixing, biological production, and size-dependent microbial reworking govern DOM dynamics in the East Sea (Sea of Japan). That coupling bulk DOC with fluorescence signatures provides a useful framework for distinguishing reactive and persistent colloidal DOM pools.</p>

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Distribution of Composition of Colloidal Organic Matter in the East Sea (Sea of Japan) Revealed by Fluorescence Spectroscopy

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  • 发表日期：

    2026年6月24日

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  • Jiyoung Lee,
  • Jeonghyun Kim

摘要

Seawater samples collected from the continental shelf, continental slope, and Ulleung Basin were fractionated using 0.45 μm, 0.2 μm, 100 kDa, and 1 kDa cutoffs and analyzed for dissolved organic carbon (DOC) and fluorescence excitation-emission matrices to investigate the size-dependent distribution and behavior of colloidal dissolved organic matter (DOM) in the East Sea (Sea of Japan). The four-component Parallel Factor Analysis model resolved two protein-like components (C1, tyrosine-like; C2, tryptophan-like) and two humic-like components (C3, terrestrial humic-like; C4, marine humic-like). The protein-like components showed maxima at the subsurface chlorophyll maximum and were positively correlated with chlorophyll a (C1: r2 = 0.66; C2: r2 = 0.61), whereas humic-like components increased with apparent oxygen utilization (AOU; C3: r2 = 0.55; C4: r2 = 0.75). Size fractionation revealed that protein-like fluorescence was relatively enriched in the larger colloidal fractions, whereas humic-like fluorescence persisted strongly in the < 100 kDa and < 1 kDa pools. When operational size classes were defined using the 1 kDa cutoff, the high-molecular-weight (HMW) DOC fraction decreased with AOU (r2 = 0.90). In contrast, the low-molecular-weight (LMW) DOC remained nearly constant, indicating a preferential remineralization of larger and more reactive DOM during water-mass aging. Surface DOC was highest in low-salinity shelf-influenced water, suggesting lateral inputs from continental shelf waters and/or terrestrial sources. Together, these results show that the combined effects of source mixing, biological production, and size-dependent microbial reworking govern DOM dynamics in the East Sea (Sea of Japan). That coupling bulk DOC with fluorescence signatures provides a useful framework for distinguishing reactive and persistent colloidal DOM pools.