Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater
Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater
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DOI：
10.3389/fmars.2020.589064
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发表时间：
2020-11
期刊：
影响因子：
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通讯作者：
Yuko Omori;A. Saeki;S. Wada;Y. Inagaki;T. Hama
中科院分区：
文献类型：
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作者：
Yuko Omori;A. Saeki;S. Wada;Y. Inagaki;T. Hama
腐殖类荧光溶解性有机物（FDOM）已被广泛用作生物难降解溶解性有机物（RDOM）的示踪剂，以了解其在海洋中的动态。腐殖类FDOM的垂直分布是由海洋内部的微生物生产和表层的光漂白控制的。虽然腐殖类FDOM预计将积极产生在表层具有高细菌活性，其生产在表层海水还没有得到很好的理解。为了研究腐殖类FDOM的日变化，由于微生物的生产和表面海水中的光漂白，我们进行了七个实验，从晚上到白天，在亚热带太平洋和沿海地区的表面海水。平行因子分析（PARAFAC）确定，在培养的海水中的FDOM是由三个组成部分：两种类型的腐殖类FDOM和蛋白质类FDOM。类腐殖酸FDOM的荧光强度在夜间增加到初始强度的104.0 ± 2.5%，在白天的阳光照射下下降到101.2 ± 2.5%。相反，在白天黑暗条件下，其强度显著增加至114.0 ± 2.7%。腐殖类FDOM的周转率的增加和减少其强度估计分别为0.14和0.11天-1。这些可比的周转率表明，生产和光漂白的腐殖类FDOM几乎处于平衡状态，在表层，与低水平的腐殖类FDOM。在黑暗条件下，在所有实验中的腐殖类FDOM的强度和溶解氧（DO）的浓度之间的线性相关性表明，腐殖类FDOM产生的微生物呼吸过程的副产品在表层海水。利用全球细菌呼吸速率估算全球透光层类腐殖酸FDOM的净产生速率为4.2-5.5 × 10 ~（17）R. U。第一年，占整个海洋产量的75%。
Humic-like fluorescent dissolved organic matter (FDOM) has been widely used as tracers for bio-refractory dissolved organic matter (RDOM) to understand its dynamics in the oceans. Vertical distributions of humic-like FDOM are controlled by microbial production in the ocean interiors and photobleaching in surface layers. Although humic-like FDOM is expected to be actively produced in surface layers with high bacterial activity, its production in surface seawater is not well understood. To examine the diurnal variations in humic-like FDOM due to microbial production and photobleaching in surface seawater, we conducted seven experiments from night to day using surface seawater in the subtropical Pacific and coastal regions. Parallel factor analysis (PARAFAC) determined that FDOM in the incubated seawater was composed of three components: two types of humic-like FDOM and a protein-like FDOM. The fluorescence intensity of humic-like FDOM increased to 104.0 ± 2.5% of the initial intensity during the night and decreased to 101.2 ± 2.5% under sunlight exposure during the day. Conversely, its intensity significantly increased to 114.0 ± 2.7% under dark conditions during the day. The turnover rates of humic-like FDOM by the increase and decrease in its intensity were estimated to be 0.14 and 0.11 day–1, respectively. These comparable turnover rates indicated that the production and photobleaching of humic-like FDOM were almost in equilibrium in the surface layer, with a low level of humic-like FDOM. Linear correlations between the intensity of humic-like FDOM and concentrations of dissolved oxygen (DO) in all experiments under dark conditions indicated that humic-like FDOM were produced as the by-products of microbial respiration processes in the surface seawater. Using global bacterial respiration rates, the net production rate of humic-like FDOM in the global photic layer was estimated as 4.2–5.5 × 1017 R.U. year–1, contributing to 75% of its production in the entire ocean.