Distribution and modulators of dissolved organic matter in the East China Sea during spring

doi:10.3969/j.issn.1000-5641.2026.03.003

Abstract

Abstract:

Dissolved organic matter (DOM) plays an essential role in marine carbon cycling by modulating carbon sequestration and ecosystem dynamics through its degradation and transformation. As the largest marginal sea in China, the East China Sea (ECS) is a critical pathway for export of terrestrially derived DOM to the Pacific Ocean. This dynamic system is influenced by multiple environmental factors, including Yangtze River inputs, Kuroshio intrusion, and anthropogenic activities, which collectively contribute to the complex sources and transformations of DOM. However, the distribution of DOM and its underlying driving factors remain understudied in the ECS. Here, measurements of dissolved organic carbon (DOC) and its optical properties (absorbance of chromophoric DOM, CDOM; excitation-emission matrices on the fluorescent DOM, EEMs on the FDOM) were made in ECS water during a cruise in spring 2023 to provide insights into the mechanisms modulating DOM variability. The results showed strong variations in both quantity and quality of DOM, with the highest DOC concentration and absorption coefficient of CDOM (a_CDOM(355)) close to the coast and decreasing offshore. DOC decreased from the surface to the bottom layer, whereas a_CDOM(355) values showed an increasing trend. Four fluorescent DOM components were resolved by parallel factor analysis: two autochthonous protein-like components, C1 and C2; one terrestrial humic-like component, C3, and one marine humic-like component, C4. The fluorescence intensity of each component decreased as distance offshore increased. Elevated fluorescence intensities of C1 and C2 were observed in the surface and bottom layers, whereas minimum values were observed in the middle layer. The fluorescence intensities of C3 and C4 decreased as water depth increased. Principal component analysis (PCA) enabled differentiation of water samples following hydrodynamic gradient. The penetrating front in the ECS resulted in enhanced cross-shelf transport of terrestrially derived DOM, while phytoplankton blooms significantly altered the amount and compositions of DOM. Overall, the DOM in the ECS in spring 2023 was primarily of terrestrial origin, while autochthonous production, microbial transformation, and bottom resuspension were collectively responsible for its variability. This study provides a fundamental framework for characterizing DOM distribution patterns in the ECS during spring.

Key words: dissolved organic matter, absorbance, fluorescence, East China Sea, penetrating front

CLC Number:

P734.2

Hongsheng CAO, Qi WU, Fang CAO. Distribution and modulators of dissolved organic matter in the East China Sea during spring[J]. J* E* C* N* U* N* S*, 2026, 2026(3): 30-43.

Figures/Tables 12

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水团名称	温度/℃	盐度
台湾暖流表层水^[14−15,17]	19.5~24.5	34.0~34.2
台湾暖流深层水^[14−15,17]	17.0~19.5	34.2~34.6
东海北部冷水^[16,19]	15.0~16.8	33.6~34.3
浙闽沿岸水^[15,18]	13.5~18.8	27.3~33.0

参数	DOC/(μmol·L^–1)		a_CDOM(355)/m^–1		S_275-295/nm^–1		SUVA₂₅₄/(L·mg^–1·m^–1)
参数	范围	平均值	范围	平均值	范围	平均值	范围	平均值
表层	63.92~122.83	85.55	0.15~0.89	0.38	0.0181~0.0359	0.0271	1.24~3.47	2.25
中层	61.57~108.58	78.78	0.16~0.88	0.39	0.0203~0.0370	0.0269	1.31~3.58	2.31
底层	62.08~100.58	76.96	0.13~1.03	0.42	0.0195~0.0309	0.0253	1.37~3.78	2.30

荧光组分	激发波长/nm	发射波长/nm	组分类型及意义	相似组分
C1	260	325	不同激发下的类色氨酸, 通常与微生物活动相关	C7^[27]
C2	280	325	不同激发下的类色氨酸, 通常与微生物活动相关	C3^[28], C5^[29]
C3	265/365	475	典型陆源类腐殖质, 具有较高分子量, 生物可利用性低	C3^[30], C2^[31]
C4	250/315	400	类腐殖质, 在海洋中原位生产, 废水中较为普遍	C1^[32], C3^[31]

荧光组分	表层荧光强度	表层平均荧光强度	中层荧光强度	中层平均荧光强度	底层荧光强度	底层平均荧光强度
C1	0.0509~0.1592	0.0873	0.0507~0.1407	0.0816	0.0506~0.1430	0.0877
C2	0.0204~0.2034	0.0706	0.0201~0.1478	0.0610	0.0278~0.1840	0.0745
C3	0.0056~0.0657	0.0259	0.0053~0.0715	0.0242	0.0068~0.0520	0.0216
C4	0.0061~0.0972	0.0258	0.0054~0.2071	0.0247	0.0105~0.0470	0.0202

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