Methane dynamics in the coastal – Continental shelf transition zone of the Gulf of Cadiz

Sierra, A.; Jiménez-López, D.; Ortega, T.; Fernández-Puga, M.C.; Huertas, António Delgado; Forja, Jesús M.

doi:10.1016/j.ecss.2020.106653

Cited by 14 publications

(10 citation statements)

References 156 publications

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“…According to the authors, the lower DOC-normalized fluorescence in the MVs, compared to those found in a reference site (without MVs), may be due to the thermal quenching of the fluorophores. Based on stable carbon isotope composition of dissolved methane in the column water above the MVs studied here, Sierra et al 31 found that methane emissions in AN and PT are of thermogenic origin, while in PI, it seems to be of biogeochemical origin. Unfortunately, we did not measure DOM composition of other pore water sediments in the zone to use as a reference site, and similar values of DOC-normalized fluorescence were observed between AN, PT and PI.…”

Section: Discussionmentioning

confidence: 80%

“…The Mg:Cl ratio indicated a higher fraction of MVs fluid in AN than in the other MVs (Fig. 4 ) and Sierra et al 31 found an increase of methane with depth in the water column above AN (100–125 nmol L −1 ) and PT (10–15 nmol L −1 ), whereas in PI this trend was not observed. This is in agreement with a previous work analyzing benthic fauna associated with seepage of MVs fluids, suggesting locally elevated gas fluxes that reach the seafloor surface, and higher activity in AN than PI 17 .…”

Section: Discussionmentioning

confidence: 86%

“…The study was carried out in three MVs: Anastasya and Pipoca, situated in the Guadalquivir Diapiric Ridge Field, and St. Petersburg, in the deeper Tasyo field, located between 457 and 860 m depth (Table S1 ). Recent work found that bottom waters at these MVs exhibit high methane concentrations, especially in AN 31 . Based on cold seep fauna at the summit of these MVs and the characteristic of the mud breccia sediments (e.g., gas bubbles, smell of H 2 S), AN seems to be the more active one among the three MVs studied here 17 .…”

Section: Methodsmentioning

confidence: 99%

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Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz

Amaral

Romera‐Castillo

Forja

2021

Sci Rep

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Seafloor structures related to the emission of different fluids, such as submarine mud volcanoes (MVs), have been recently reported to largely contribute with dissolved organic matter (DOM) into the oceans. Submarine MVs are common structures in the Gulf of Cádiz. However, little is known about the biogeochemical processes that occur in these peculiar environments, especially those involving DOM. Here, we report DOM characterization in the sediment pore water of three MVs of the Gulf of Cádiz. Estimated benthic fluxes of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) were higher than in other marine sediments with an average of 0.11 ± 0.04 mmol m−2 d−1 for DOC and ranging between 0.11 and 2.86 m−1 L m−2 d−1, for CDOM. Protein-like components represented ~ 70% of the total fluorescent DOM (FDOM). We found that deep fluids migration from MVs (cold seeps) and anaerobic production via sulfate-reducing bacteria represent a source of DOC and FDOM to the overlying water column. Our results also indicate that fluorescent components can have many diverse sources not captured by common classifications. Overall, MVs act as a source of DOC, CDOM, and FDOM to the deep waters of the Gulf of Cádiz, providing energy to the microbial communities living there.

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Section: Discussionmentioning

confidence: 80%

Section: Discussionmentioning

confidence: 86%

Section: Methodsmentioning

confidence: 99%

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Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz

Amaral

Romera‐Castillo

Forja

2021

Sci Rep

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“…Since seeps are mostly located with water depth >50 m, MOx rates were not impacted by seeps in shallow waters (0-50 m). To exclude seeps for waters depths between 50-200 m, data were filtered based on the methane concentrations: seep ≥10 nM CH 4 and non-seep <10 nM CH 4 , as methane concentrations were typically <10 nM in nonseep areas based on this study and a number of previous observations 15,27,55,56 . The average MOx rates from different depths throughout water column in the near-shore and out-shelf waters were also predicted using vertical profiles of methane and other variables from the database (Fig.…”

Section: Machine-learning Prediction Of Global Mox Ratesmentioning

confidence: 99%

Aerobic oxidation of methane significantly reduces global diffusive methane emissions from shallow marine waters

et al. 2022

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Methane is supersaturated in surface seawater and shallow coastal waters dominate global ocean methane emissions to the atmosphere. Aerobic methane oxidation (MOx) can reduce atmospheric evasion, but the magnitude and control of MOx remain poorly understood. Here we investigate methane sources and fates in the East China Sea and map global MOx rates in shallow waters by training machine-learning models. We show methane is produced during methylphosphonate decomposition under phosphate-limiting conditions and sedimentary release is also source of methane. High MOx rates observed in these productive coastal waters are correlated with methanotrophic activity and biomass. By merging the measured MOx rates with methane concentrations and other variables from a global database, we predict MOx rates and estimate that half of methane, amounting to 1.8 ± 2.7 Tg, is consumed annually in near-shore waters (<50 m), suggesting that aerobic methanotrophy is an important sink that significantly constrains global methane emissions.

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“…We measured CH 4 and N 2 O by duplicate using headspace equilibration. A quantity of 25 g (± 0.01 g) of water samples was taken using a 50 mL glass syringe (Agilent P/N 5190-1547) (Sierra et al 2017(Sierra et al , 2020. A volume of 25 mL with the standard gas mixture of CH 4 and N 2 O concentrations similar to atmospheric values (1952 and 304 ppbv, respectively) was used to complete the volume of the syringe.…”

Section: Determination Of Dissolved Ch 4 and N 2 Omentioning

confidence: 99%

Linkages between greenhouse gases (CO2, CH4, and N2O) and dissolved organic matter composition in a shallow estuary

Amaral

Ortega

Romera‐Castillo

et al. 2021

Science of The Total Environment

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Methane dynamics in the coastal – Continental shelf transition zone of the Gulf of Cadiz

Cited by 14 publications

References 156 publications

Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz

Submarine mud volcanoes as a source of chromophoric dissolved organic matter to the deep waters of the Gulf of Cádiz

Aerobic oxidation of methane significantly reduces global diffusive methane emissions from shallow marine waters

Linkages between greenhouse gases (CO2, CH4, and N2O) and dissolved organic matter composition in a shallow estuary

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