Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water

Zhang, Yong; Xie, Huixiang

doi:10.5194/bg-12-6823-2015

Cited by 37 publications

(44 citation statements)

References 79 publications

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“…To our knowledge, the potential influence of irradiation history on the DOC loss-to-CDOM loss ratio for open oceans has not been evaluated. Terrestrial CDOM has shown rather constancy of the DOC-to-CDOM ratio up to 55-80% absorbance losses but displayed significant increases under further photobleaching (Qi et al, 2018;Zhang & Xie, 2015), which underestimates our photomineralization fluxes if deep-ocean CDOM behaves similarly. This underestimation, if any, is plausibly inconsequential, since the rate of photomineralization decreases with increasing photobleaching of CDOM in marine waters (Powers et al, 2017).…”

Section: Implications For Deep-ocean Rdom Cyclingmentioning

confidence: 54%

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

et al. 2020

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Water samples collected from various depths of the offshore South China and Philippine Seas were exposed to solar‐simulated radiation. Photomineralization of dissolved organic carbon (DOC) and photobleaching of chromophoric dissolved organic matter (CDOM) and its humic‐like fluorescent constituent (FDOM) were observed in all samples. Protein‐like FDOM was, however, either photo‐decomposed or photo‐produced, depending on the sample's depth. The photobleaching of CDOM and humic‐like FDOM was much faster in deep than in shallow water samples while photomineralization displayed a weaker vertical zonation. Prior‐irradiated deep water inoculated with surface‐water bacteria showed enhanced microbial DOC removal but CDOM production. Results from this study suggest that deep‐ocean CDOM and FDOM can barely survive photobleaching during one ocean mixing cycle, but photochemical turnover of the bio‐refractory deep DOC is considerably longer than its average radiocarbon age. Coupled photochemical‐microbial processes can not only remove part of the bio‐refractory deep DOM but also regenerate part of it during ocean overturning circulation.

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Section: Implications For Deep-ocean Rdom Cyclingmentioning

confidence: 54%

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

et al. 2020

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“…It has been suggested that some methanogens might be active under oxic conditions by being equipped with enzymes to counteract the effects of molecular oxygen during methanogenesis (Angel et al, 2011). Potential substrates for methylotrophic methanogens in such micro-niches are the algae metabolites dimethylsulfoniopropionate (DMSP) and their degradation products dimethyl sulfide (DMS) or dimethyl sulfoxide (DMSO) (Zindler et al, 2013;Damm et al, 2008;Florez-Leiva et al, 2013). Furthermore, DMSP might also be converted to CH 4 by nitrogenlimited bacteria (Damm et al, 2010(Damm et al, , 2015.…”

Section: Introductionmentioning

confidence: 99%

Methane production by three widespread marine phytoplankton species: release rates, precursor compounds, and potential relevance for the environment

et al. 2019

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Abstract. Methane (CH4) production within the oceanic mixed layer is a widespread phenomenon, but the underlying mechanisms are still under debate. Marine algae might contribute to the observed CH4 oversaturation in oxic waters, but so far direct evidence for CH4 production by marine algae has only been provided for the coccolithophore Emiliania huxleyi. In the present study we investigated, next to E. huxleyi, other widespread haptophytes, i.e., Phaeocystis globosa and Chrysochromulina sp. We performed CH4 production and stable carbon isotope measurements and provide unambiguous evidence that all three investigated marine algae are involved in the production of CH4 under oxic conditions. Rates ranged from 1.9±0.6 to 3.1±0.4 µg of CH4 per gram of POC (particulate organic carbon) per day, with Chrysochromulina sp. and E. huxleyi showing the lowest and highest rates, respectively. Cellular CH4 production rates ranged from 16.8±6.5 (P. globosa) to 62.3±6.4 ag CH4 cell−1 d−1 (E. huxleyi; ag = 10−18 g). In cultures that were treated with 13C-labeled hydrogen carbonate, δ13CH4 values increased with incubation time, resulting from the conversion of 13C–hydrogen carbonate to 13CH4. The addition of 13C-labeled dimethyl sulfide, dimethyl sulfoxide, and methionine sulfoxide – known algal metabolites that are ubiquitous in marine surface layers – resulted in the occurrence of 13C-enriched CH4 in cultures of E. huxleyi, clearly indicating that methylated sulfur compounds are also precursors of CH4. By comparing the algal CH4 production rates from our laboratory experiments with results previously reported in two field studies of the Pacific Ocean and the Baltic Sea, we might conclude that algae-mediated CH4 release is contributing to CH4 oversaturation in oxic waters. Therefore, we propose that haptophyte mediated CH4 production could be a common and important process in marine surface waters.

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“…Analyses [CH 4 ] in seawater was measured onboard immediately after sampling at a rate of 6-8 samples per hour. A static headspace method was adopted (Zhang and Xie, 2015). Briefly, water samples were transferred to a 50-mL glass syringe fitted with three-way valves (glass fiber reinforced polypropylene, GFPP).…”

Section: Samplingmentioning

confidence: 99%

“…Bange and Uher (2005) assessed the possibility of this source from CDOM in river and estuarine systems and concluded that this pathway is significant only under anoxia in the presence of added methyl radical precursor (acetone). By irradiating water samples under simulated sunlight and then measuring the increase rate of [CH 4 ] with prolonged irradiation time, Zhang and Xie (2015) found that photomethanification in river water occurred under both suboxic and oxic conditions, with the rate under suboxic conditions being 7-8 times higher than that under oxic conditions, and that an addition of micromolar levels of methyl radical precursor (DMS) greatly accelerated this process. However, no information is yet available on the photoproduction of CH 4 in the Bohai Sea.…”

Section: The Variation In Depth-integrated [Ch 4 ] Over a Certain Timmentioning

confidence: 99%

“…Sources of CH 4 in coastal waters can be roughly divided into in situ processes (within the water column) and ex situ processes (outside of the water column). In situ processes include (1) biological CH 4 production (methanogenesis) under anoxic conditions and subsequent release from the fecal pellet microenvironment (Karl and Tilbrook, 1994;Tilbrook and Karl, 1995) and/or, under oxic conditions, through decomposition of methylated precursors, such as methylphosphonates (Karl et al, 2008;Metcalf et al, 2012) and dimethylsulfoniopropionate (DMSP) and/or dimethylsulfoxide (DMSO) (Damm et al, 2008(Damm et al, , 2015Weller et al, 2013;Zindler et al, 2013) and (2) photochemical production from precursors of methyl radical (Bange and Uher, 2005;Zhang and Xie, 2015). Ex situ processes usually refer to (1) CH 4 release from the seafloor, including release from sediment due to diagenesis of buried organic matter Sun et al, 2018) and release from other natural geological settings such as submarine hydrocarbon seeps (e.g., Boles et al, 2001;Reeburgh, 2007) and (2) CH 4 addition from river runoffs, which is significant in estuarine areas (e.g., Ye et al, 2016;Sun et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

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Exploring Sources and Biogeochemical Dynamics of Dissolved Methane in the Central Bohai Sea in Summer

2020

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To clarify the sources and biogeochemical dynamics of dissolved methane (CH 4 ) in shallow-water coastal oceans, we investigated the concentrations, sea-to-air fluxes, and net cycling rate of CH 4 in the central Bohai Sea in summer 2018. During the survey, both summertime stratification and dissolved oxygen (DO) deficit were observed. In the surface layer, CH 4 concentration ([CH 4 ]) ranged from 3.08 to 10.27 nmol kg −1 . The average sea-to-air flux was estimated at 6.46 ± 3.32 µmol m −2 d −1 , indicating that the Bohai Sea serves as a source of atmospheric CH 4 . In the bottom layer, [CH 4 ] ranged from 4.29 to 31.04 nmol kg −1 . The downward increase in [CH 4 ] within the water column indicated substantial sources of CH 4 in the seafloor. Based on the complex relationship between the saturation ratio of CH 4 and DO, three types of CH 4 release from the seafloor were identified, including diagenesis of buried organic matter, natural leakage from geological settings, and anthropogenic release from offshore oil/gas development. The saturation ratios of CH 4 in bottom waters were positively correlated with the degree of stratification of the water column. Using a two-layer box model, sedimentary CH 4 release rates at two oxygen-deficient stations were estimated to be 56.0-60.8 µmol m −2 d −1 , which was much higher than the sea-to-air fluxes. The modeling results also indicated that the majority of seafloor released CH 4 (>90%) was consumed in the water column of this shallow-water coastal sea. This is the first comprehensive study on CH 4 cycling in the Bohai Sea. This work shows the indicative role of DO in identifying multiple CH 4 sources and highlights the dominance of water stratification and microbial consumption in local CH 4 dynamics. KEY POINTS -Dissolved CH 4 exhibited complex relations with oxygen in the Bohai Sea. -Three types of CH 4 sources from seafloor were identified. -Stratification hampered the upward transport of dissolved CH 4 . -Strengths of CH 4 cycling terms are quantified.

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Photomineralization and photomethanification of dissolved organic matter in Saguenay River surface water

Cited by 37 publications

References 79 publications

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

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

Methane production by three widespread marine phytoplankton species: release rates, precursor compounds, and potential relevance for the environment

Exploring Sources and Biogeochemical Dynamics of Dissolved Methane in the Central Bohai Sea in Summer

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