Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater
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 photobleachi...
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2020-11-01
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| Series: | Frontiers in Marine Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fmars.2020.589064/full |
| _version_ | 1818936624432545792 |
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| author | Yuko Omori Akira Saeki Shigeki Wada Yuji Inagaki Takeo Hama Takeo Hama |
| author_facet | Yuko Omori Akira Saeki Shigeki Wada Yuji Inagaki Takeo Hama Takeo Hama |
| author_sort | Yuko Omori |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-12-20T05:39:01Z |
| format | Article |
| id | doaj.art-fb0bfde2092640029270c4d70ba073a1 |
| institution | Directory Open Access Journal |
| issn | 2296-7745 |
| language | English |
| last_indexed | 2024-12-20T05:39:01Z |
| publishDate | 2020-11-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Marine Science |
| spelling | doaj.art-fb0bfde2092640029270c4d70ba073a12022-12-21T19:51:31ZengFrontiers Media S.A.Frontiers in Marine Science2296-77452020-11-01710.3389/fmars.2020.589064589064Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface SeawaterYuko Omori0Akira Saeki1Shigeki Wada2Yuji Inagaki3Takeo Hama4Takeo Hama5Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, JapanGraduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, JapanShimoda Marine Research Center, University of Tsukuba, Shimoda, JapanCenter for Computational Sciences, University of Tsukuba, Tsukuba, JapanFaculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, JapanFaculty of Economics, Dokkyo University, Souka, JapanHumic-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.https://www.frontiersin.org/articles/10.3389/fmars.2020.589064/fullfluorescent dissolved organic matterPARAFACmicrobial productionphotobleachingsurface seawater |
| spellingShingle | Yuko Omori Akira Saeki Shigeki Wada Yuji Inagaki Takeo Hama Takeo Hama Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater Frontiers in Marine Science fluorescent dissolved organic matter PARAFAC microbial production photobleaching surface seawater |
| title | Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater |
| title_full | Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater |
| title_fullStr | Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater |
| title_full_unstemmed | Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater |
| title_short | Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater |
| title_sort | experimental analysis of diurnal variations in humic like fluorescent dissolved organic matter in surface seawater |
| topic | fluorescent dissolved organic matter PARAFAC microbial production photobleaching surface seawater |
| url | https://www.frontiersin.org/articles/10.3389/fmars.2020.589064/full |
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