Benthic fluxes of dissolved organic carbon from gas hydrate sediments in the northern South China Sea

Hung, Chia Wei; Huang, Ke; Shih, Yung Yen; Lin, Yu-Ju; Chen, Hsin Hung; Wang, Chau Chang; Ho, C.-Y.; Hung, Chin Chang; Burdige, David J.

doi:10.1038/srep29597

Cited by 16 publications

(6 citation statements)

References 39 publications

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“…As we mentioned above, carbon entering the seawater from the sediments in the form of DIC and DOM can also, to some extent, influence the deep ocean carbon cycling, especially the carbonate saturation state in the water column [82,83]. In the hydrate-bearing area of the northern SCS, DOM effluxes in the form of aqueous methane werẽ 5 mmol·m -2 ·yr -1 (see Figure 4).…”

Section: Influence Of Shallow Carbon Cycling On the Carbonmentioning

confidence: 95%

“…Irrespective of gaseous methane in the intensive gas seepage sites, such considerable amounts of DOM diffusing towards the bottom water may play an important role in the DOM cycling in the deep waters of the northern SCS. Recent studies have shown much greater DOM fluxes (0.1 mol·m -2 ·yr -1 ) by accounting for other forms of DOM species such as volatile fatty acids [80,83]. Thus, the widely distributed gas hydrates and cold seeps in the northern SCS could contribute far more than 9 × 10 −5 Tmol DOM/yr to the ocean if gaseous methane and other organic acids are incorporated into the flux calculation.…”

Section: Influence Of Shallow Carbon Cycling On the Carbonmentioning

confidence: 99%

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An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Zhang

Luo

et al. 2019

Geofluids

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Gas hydrates, acting as a dynamic methane reservoir, store methane in the form of a solid phase under high-pressure and low-temperature conditions and release methane through the sediment column into seawater when they are decomposed. The seepage of methane-rich fluid (i.e., cold hydrocarbon seeps) fuels the chemosynthetic biota-inhabited surface sediments and represents the major pathway to transfer carbon from sediments to the water column. Generally, the major biogeochemical reactions related to carbon cycling in the anoxic marine sediments include organic matter degradation via sulfate reduction (OSR), anaerobic oxidation of methane (AOM), methanogenesis (ME), and carbonate precipitation (CP). In order to better understand the carbon turnover in the cold seeps and gas hydrate-bearing areas of the northern South China Sea (SCS), we collected geochemical data of 358 cores from published literatures and retrieved 37 cores and corresponding pore water samples from three areas of interest (i.e., Xisha, Dongsha, and Shenhu areas). Reaction-transport simulations indicate that the rates of organic matter degradation and carbonate precipitation are comparable in the three areas, while the rates of AOM vary over several orders of magnitude (AOM: 8.3-37.5 mmol·m-2·yr-1 in Dongsha, AOM: 12.4-170.6 mmol·m-2·yr-1 in Xisha, and AOM: 9.4-30.5 mmol·m-2·yr-1 in Shenhu). Both the arithmetical mean and interpolation mean of the biogeochemical processes were calculated in each area. Averaging these two mean values suggested that the rates of organic matter degradation in Dongsha (25.7 mmol·m-2·yr-1) and Xisha (25.1 mmol·m-2·yr-1) are higher than that in Shenhu (12 mmol·m-2·yr-1) and the AOM rate in Xisha (135.2 mmol·m-2·yr-1) is greater than those in Dongsha (27.8 mmol·m-2·yr-1) and Shenhu (17.5 mmol·m-2·yr-1). In addition, the rate of carbonate precipitation (32.3 mmol·m-2·yr-1) in Xisha is far higher than those of the other two regions (5.3 mmol·m-2·yr-1 in Dongsha, 5.8 mmol·m-2·yr-1 in Shenhu) due to intense AOM sustained by gas dissolution. In comparison with other cold seeps around the world, the biogeochemical rates in the northern SCS are generally lower than those in active continental margins and special environments (e.g., the Black sea) but are comparable with those in passive continental margins. Collectively, ~2.8 Gmol organic matter was buried and at least ~0.82 Gmol dissolved organic and inorganic carbon was diffused out of sediments annually. This may, to some extent, have an impact on the long-term deep ocean carbon cycle in the northern SCS.

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Section: Influence Of Shallow Carbon Cycling On the Carbonmentioning

confidence: 95%

Section: Influence Of Shallow Carbon Cycling On the Carbonmentioning

confidence: 99%

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Zhang

Luo

et al. 2019

Geofluids

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“…Chl-a concentrations were measured with a Turner Designed 10-AU-005 fluorometer using the non-acidification method (Gong et al, 1996;Shih et al, 2019). Concentrations of TSM and POC were measured following the methods of Hung et al (2013) while DOC was measured by the method of Hung et al (2016). The ecological water quality state (European Commission, 2000) was used to classify the conditions of water in Negombo lagoon.…”

Section: Sampling Site and Hydrographic Parameter Analysismentioning

confidence: 99%

Eutrophication and Hypoxia in Tropical Negombo Lagoon, Sri Lanka

et al. 2021

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Hypoxic events are becoming frequent in some estuaries and coastal waters due to over-enrichment of anthropogenic nutrients, organic matter, and/or due to restricted water circulation. The coastal lagoons and estuaries of Sri Lanka are facing high population pressure and lacking sufficient infrastructure. Coastal lagoons may receive high anthropogenic inputs of natural or untreated nitrogen and phosphorus wastes, and consequently result in hypoxic conditions while sluggish circulation occurred. In this study, we examined the spatiotemporal variability of eutrophication and hypoxia in the Negombo Lagoon, one of the most productive and sensitive coastal ecosystems in Sri Lanka. Based on seasonal measurements of dissolved oxygen, nutrients, chlorophyll-a (Chl-a), particulate and dissolved organic carbon (POC and DOC), we concluded that eutrophication and hypoxia occurred in both the dry and wet seasons. The main contributing factors were high seawater temperature and poor water circulation in the dry season and high nutrient loading combined with elevated POC and DOC inputs in the wet season.

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“…In addition to POC mineralization, DOC production in seepimpacted sediments is closely associated with the anaerobic oxidation of methane (AOM; Pohlman et al, 2011). As a result, significantly higher DOC concentrations have been observed in seep sediments compared to non-seep deep sea sediments (Hung et al, 2016;Amaral et al, 2021). Valentine et al (2005) found that the proportion of methane-derived DOC increases with enhanced AOM rates and microbial activity in the cold seep sediments.…”

Section: Introductionmentioning

confidence: 99%

Production of Labile Protein-Like Dissolved Organic Carbon Associated With Anaerobic Methane Oxidization in the Haima Cold Seeps, South China Sea

Luo

et al. 2021

Front. Mar. Sci.

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Cold seeps where methane-rich fluids escape from the seafloor generally support enormous biomass of chemosynthetic organisms and associated fauna. In addition to transporting a great amount of methane toward the seafloor, cold seeps also contribute to the aged, dissolved organic carbon (DOC) pool in the deep ocean. Here, two sediment cores from the “Haima cold seeps,” northern South China Sea and a nearby reference core were analyzed for pore-water sulfate and DOC concentrations, δ13C of DOC, and optical properties of dissolved organic matter (DOM). High DOC concentrations (0.9–3.7 mM) accompanied by extremely low δ13C values (−43.9 to −76.2‰) suggest the conversion of methane into sedimentary DOC pool in the seep sediments. Parallel factor analysis (PARAFAC) of the fluorescence excitation-emission matrices shows higher fluorescent intensities of labile protein-like components (C2 and C4) and lower fluorescent intensities of refractory humic-like components (C1 and C3) in the seep cores compared to the reference core. The intensity of C2 is positively correlated with DOC concentrations and δ13C-DOC in the seep sediments, suggesting that the labile protein-like DOM was produced by the anaerobic oxidation of methane (AOM). Moreover, low humification index (HIX) and high biological index (BIX) values also indicate intensified production of relatively labile DOM with lower degradation degree in the seep cores compared to the reference core. Hence, we highlight that methane-derived DOC may serve as important carbon and energy sources for heterotrophic microbial communities due to its relatively labile nature.

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Benthic fluxes of dissolved organic carbon from gas hydrate sediments in the northern South China Sea

Cited by 16 publications

References 39 publications

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

An Areal Assessment of Subseafloor Carbon Cycling in Cold Seeps and Hydrate-Bearing Areas in the Northern South China Sea

Eutrophication and Hypoxia in Tropical Negombo Lagoon, Sri Lanka

Production of Labile Protein-Like Dissolved Organic Carbon Associated With Anaerobic Methane Oxidization in the Haima Cold Seeps, South China Sea

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