Depth‐Resolved Photochemical Lability of Dissolved Organic Matter in the Western Tropical Pacific Ocean

Yang, Fangming; Song, Guisheng; Massicotte, Philippe; Wei, Hao; Xie, Huixiang

doi:10.1029/2019jg005425

Cited by 17 publications

(13 citation statements)

References 65 publications

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“…There are some stations with higher humic-like components (C2-C4) in bottom water than in surface water in Jiaozhou Bay, although there is higher DOM abundance in surface water than in bottom water in most stations of Jiaozhou Bay. These results are consistent with that humic-like components are more susceptible to photodegradation (Lønborg et al, 2015;Yang et al, 2020). Moreover, there are higher S 275-295 in surface water than that in bottom water in most stations of Sishili Bay, indicating photobleaching is an important factor influencing surface DOM.…”

Section: Multiple Mechanisms Controlling the Vertical Distribution Of Dissolved Organic Mattersupporting

confidence: 85%

Anthropogenic Influences on Dissolved Organic Matter in Three Coastal Bays, North China

Zhao

Liu

et al. 2021

Front. Earth Sci.

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Coastal bays bear anthropogenic influence strongly, and thus dissolved organic matter (DOM) in coastal bays, which is an important component of global carbon cycling, could be heavily affected by anthropogenic inputs. Utilizing absorbance, fluorescence spectroscopy, and stable carbon isotope (δ13C), this study analyzed the characteristics and distribution of DOM in three coastal bays (Jiaozhou Bay, Sishili Bay, and Taozi Bay), located in North China. The results showed that there was always a high concentration of DOM near the river mouth in all three bays and the DOM concentration decreased along the salinity gradient in Jiaozhou Bay, indicating the riverine inputs are the main factor that causes the variation of DOM in these coastal bays. The effects of inflowing rivers on DOM in coastal bays differed with their watershed characteristics (i.e., agricultural/urban). In addition, humic-like DOM components were found to be positively correlated with the apparent oxygen utilization, suggesting microbial activities could contribute to the DOM in this region. There was generally a higher averaged concentration of fluorescent DOM in surface water than that in bottom water in Jiaozhou Bay. In contrast, higher humic-like DOM was found in bottom water than that in surface water in Sishili Bay and Taozi Bay, which could be attributed to aquaculture activities and biological production. Moreover, photodegradation/photobleaching, dumping, and sewage discharge had their effects on DOM in coastal bays. This study demonstrates that DOM in coastal bays is regulated by multiple sources (rivers, aquaculture, dumping, and sewage) and processes (biological production and photodegradation), and anthropogenic activities have their influences on optical and isotopic characteristics of DOM in coastal bays.

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Section: Multiple Mechanisms Controlling the Vertical Distribution Of Dissolved Organic Mattersupporting

confidence: 85%

Anthropogenic Influences on Dissolved Organic Matter in Three Coastal Bays, North China

Zhao

Liu

et al. 2021

Front. Earth Sci.

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“…However, the short turnover of humic-like FDOM implied a short life of its fluorophore, without reflecting the behaviors of organic carbon. Photobleached FDOM has been reported to undergo different processes after sunlight exposure: mineralization (Mopper et al, 1991), formation of low-molecular DOM, including oxygenated volatile organic compounds (Kieber et al, 1990;Mopper et al, 1991;Zhou and Mopper, 1997), transformation to biological labile DOM to be consumed by bacteria (Moran et al, 2000;Yang et al, 2020), and remaining as RDOM without the fluorescent property (Kramer and Herndl, 2004). Although no method exists for measuring FDOM lost fluorophore, it has been considered that it may remain as organic substances as post-FDOM (Omori et al, 2015).…”

Section: Importance Of Photobleached Humic-like Fdom In Biogeochemicamentioning

confidence: 99%

Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater

et al. 2020

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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 humiclike 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 humiclike 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 × 10 17 R.U. year −1 , contributing to 75% of its production in the entire ocean.

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“…Thus, we conclude that DOM in the high-salinity water of the northern Beibu Gulf is dominated by terrestrial input and microbial reworking. Cultural experiments confirm that both terrestrial and microbialderived DOM with low S 275−295 can be easily degraded by light radiation (Helms et al, 2013;Yang et al, 2020). It can be expected that DOM in the high-salinity water of the northern Beibu Gulf also has a large potential for photodegradation, when it was transported into the upper stratified layer of the adjacent South China Sea (Chen et al, 2011).…”

Section: Sources Of Dom In Northern Beibu Gulfmentioning

confidence: 97%

Distribution, spectral characteristics, and seasonal variation of dissolved organic matter in the northern Beibu Gulf, South China Sea

Zhu

Wei²,

Guan³

et al. 2022

Front. Mar. Sci.

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Dissolved organic matter (DOM) in the land–ocean interface plays a critical role in the global carbon cycle, yet its dynamic is not well understood. Dissolved organic carbon (DOC) in the northern Beibu Gulf was measured seasonally from April 2020 to January 2021. Chromophoric and fluorescent DOM (CDOM and FDOM) were synchronously characterized by absorption and fluorescence spectroscopy. Three fluorescent components were identified from 597 samples using parallel factor analysis, including two humic-like and one protein-like component. DOC displays a significant seasonality with the average level being highest in summer (177 μmol/L) and lowest in winter (107 μmol/L). CDOM and FDOM levels in summer are also higher than those in winter. Although the variation ranges of DOC, CDOM, and FDOM in surface water are generally greater than in bottom water, the difference between the two layers is statistically insignificant. River discharge and anthropogenic input are important external sources of DOM in the low-salinity nearshore waters (i.e., estuaries and coast), whereas DOM in offshore waters is mainly produced by in situ biological activity. The mixing behavior of DOM in the northern Beibu Gulf varies spatially but minimally on a seasonal scale. Two distinct conservative mixing behaviors of DOC, CDOM, and humic-like FDOM occur in the nearshore waters from Tieshangang Bay and excluding Tieshangang Bay, respectively. The removal of protein-like FDOM along the salinity gradient and the negative correlation between protein-like FDOM intensity and apparent oxygen utilization are pronounced in the nearshore waters excluding Tieshangang Bay, jointly indicating that oxygen is consumed by microbial communities. In contrast, a net addition of DOC occurs in the high-salinity offshore waters, whereas the CDOM and humic-like FDOM undergoes quasi-conservative mixing. Overall, this study reveals notable spatial and seasonal variations in the concentration, source, and mixing of DOM at the land–ocean interface and highlights the importance of sources and processes in shaping the amount and composition of DOM exported to the ocean margin.

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Depth‐Resolved Photochemical Lability of Dissolved Organic Matter in the Western Tropical Pacific Ocean

Cited by 17 publications

References 65 publications

Anthropogenic Influences on Dissolved Organic Matter in Three Coastal Bays, North China

Anthropogenic Influences on Dissolved Organic Matter in Three Coastal Bays, North China

Experimental Analysis of Diurnal Variations in Humic-Like Fluorescent Dissolved Organic Matter in Surface Seawater

Distribution, spectral characteristics, and seasonal variation of dissolved organic matter in the northern Beibu Gulf, South China Sea

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