Dissolved methane in the East China Sea: Distribution, seasonal variation and emission

Sun, Miao; Zhang, G.-L.; Ma, Xiao; Cao, Xihua; Mao, Xinyan; Li, J.; Ye, W.-W.; Liu, S.-M.

doi:10.1016/j.marchem.2018.03.001

Cited by 32 publications

(22 citation statements)

References 67 publications

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“…Previous studies have indicated that in situ CH 4 formation in oxygenated waters might be an important source of CH 4 in the marginal seas of the WNP (Ye et al 2016(Ye et al , 2019Sun et al 2018); however, the potential precursor for this process remains ambiguous. Our results showed that MPn addition resulted in enhanced CH 4 production in coastal water, thereby suggesting the relevance of CH 4 production and microbial MPn degradation.…”

Section: Mpn-dependent Ch 4 Production In the Eutrophic Yellow Seamentioning

confidence: 99%

“…Although Pi is the major form (70%) of dissolved P, the concentration of dissolved organic phosphorus (DOP) is generally higher than that of Pi in surface waters (Fang 2004). Studies have shown that surface CH 4 supersaturation is ubiquitous in the coastal seas of the WNP (Ye et al 2016(Ye et al , 2019Sun et al 2018). However, the mechanism of CH 4 accumulation in oxygenated surface water and the connections between the P cycle and CH 4 paradox are poorly understood.…”

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confidence: 99%

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Methane production in oxic seawater of the western North Pacific and its marginal seas

Wang

Zhang

et al. 2020

Limnology & Oceanography

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The oceans are natural sources of atmospheric methane (CH 4), but the origin of excess CH 4 at the surface remains enigmatic. Incubation experiments were conducted in the western North Pacific (WNP) and its marginal seas (i.e., Yellow Sea and South China Sea [SCS]) to identify the degradation of methylphosphonate (MPn) to CH 4 in the oceans and the microbes associated with MPn-driven CH 4 production. In the coastal seawater of the Yellow Sea, CH 4 was observed to accumulate after MPn enrichment with a high MPn to CH 4 conversion efficiency (approximately 60%). Dissolved inorganic phosphorus (Pi) did not effectively restrict the microbial utilization of MPn in the eutrophic coastal waters. The results of 16S rRNA gene sequencing showed that Vibrio spp. were the dominant bacteria in the MPn-amended treatments. Moreover, several Vibrio isolates isolated from the coastal waters were found to produce CH 4 while growing in culture using MPn as the sole P source, thereby indicating that Vibrio spp. might be the major contributors to MPn-dependent CH 4 production. In oligotrophic areas, such as the SCS and WNP, CH 4 production from MPn metabolism was also observed in the surface seawater. In contrast to coastal waters, this pathway in oligotrophic areas is regulated by dissolved Pi availability. This work confirms that aerobic CH 4 formation from MPn degradation can occur both in eutrophic coastal waters and oligotrophic oceans driven by MPn-utilizing microorganisms (especially heterotrophic bacteria), which may have a significant impact on our understanding of the CH 4 and P cycles in global oceans. Methane (CH 4) is a greenhouse gas that plays an important role in global warming. Oceans are a natural source of atmospheric CH 4 and contribute 1-4% of the annual global emissions (IPCC 2013). Studies have shown that the oxygenated surface waters throughout the majority of the global oceans are supersaturated with CH 4 with respect to the atmosphere, thereby implying a local CH 4 source. However, the origin of oceanic surface CH 4 is not sufficiently understood (Reeburgh 2007). Traditional CH 4 production is thought to be a strictly anaerobic process mediated by methanogenic archaea, which are outperformed by sulfate-reducing bacteria when competing for potential substrates (such as H 2 and acetate) (Sorokin et al. 2017). Methanogenesis appears to be inhibited by the presence of well-mixed oxygen and sulfate in the ocean surface. However, recent studies have shown that methylated compounds, such as

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Section: Mpn-dependent Ch 4 Production In the Eutrophic Yellow Seamentioning

confidence: 99%

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confidence: 99%

Methane production in oxic seawater of the western North Pacific and its marginal seas

Wang

Zhang

et al. 2020

Limnology & Oceanography

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“…The CH 4 concentrations of the P2 and P3 transects unveiled a noticeable shelf-to-slope trend, which increased and then decreased with distance from the shelf. On the continental shelf with shallow water depth, all sites were characterized by relatively high CH 4 concentration, with the value > 10 nM, especially in surface waters, which may be influenced by shelf mixed water (Ye et al, 2016;Sun et al, 2018). However, the maximum values in both transects appeared on the slope.…”

Section: Distribution Of Ch 4 Across the Shelf And Slopementioning

confidence: 90%

“…The SMW distributed in the shelf edge zone included Changjiang Diluted Water (CDW), TWCW, and Kuroshio Surface Water (KSW) (Zhang et al, 2007;Ye et al, 2016). Previous studies reported that a small number of large rivers in East Asia (Sieburth, 1987) were transporting huge amounts of freshwater along with high concentrations of dissolved CH 4 to the ECS, e.g., about 70.6 × 10 6 mol yr −1 CH 4 , were imported from the Changjiang (112-190 nM in the surface water in spring) to the ECS (Tsurushima et al, 1996;Zhang et al, 2004;Ye et al, 2016;Sun et al, 2018). It is noteworthy that dissolved CH 4 in the river water is almost 2 orders of magnitude higher than that found in the continental shelf edge (Sun et al, 2018), and in summer, this river water mass extends further to the continental shelf, which may justify the relatively high CH 4 concentration in this area.…”

Section: Distribution Of Ch 4 Across the Shelf And Slopementioning

confidence: 99%

Distribution and Discharge of Dissolved Methane in the Middle Okinawa Trough, East China Sea

et al. 2020

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Widespread seepage of methane from seafloor sediments on continental margins are released into seawater, a portion of which may escape to the atmosphere. To assess the water column distribution characteristics of methane and its input to the atmosphere, we investigated methane emissions from the shelf and west slope of the back-arc Okinawa Trough (OT), East China Sea. Our results showed a heterogeneity distribution of methane within the water column. The highest value, which was more than 10 times of the background concentration, occurred near a cold seep in the north of the study area which was discovered by a remotely operated underwater vehicle (ROV). Other sources of methane to the water column of the OT, besides cold seepage input, probably also include in situ aerobic methane production, advective transport from the continental shelf, and/or hydrothermal venting. Furthermore, the sea-to-air flux of methane throughout the study area was up to 116 µmol m −2 d −1 , noticeably higher than that in many other continental shelf waters and seep sites globally, indicating that this region is an active CH 4 emission area. Our findings demonstrate that methane discharged from both cold seeps and hydrothermal vents have a significant influence on the methane cycle in the OT, providing a new insight for the methane budget of back-arc basins.

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“…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). In addition, anthropogenic eutrophication (e.g., Naqvi et al, 2010;Borges et al, 2016) and episodic oil-gas leakages (e.g., Zhang et al, 2014;Zhang and Zhai, 2015) can enhance the CH 4 concentration in the overlying water column.…”

Section: Introductionmentioning

confidence: 99%

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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Dissolved methane in the East China Sea: Distribution, seasonal variation and emission

Cited by 32 publications

References 67 publications

Methane production in oxic seawater of the western North Pacific and its marginal seas

Methane production in oxic seawater of the western North Pacific and its marginal seas

Distribution and Discharge of Dissolved Methane in the Middle Okinawa Trough, East China Sea

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

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