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

Sun, Mingshuang, Zhang, G.-L., Ma, X., Cao, X.-P., Mao, X.-Y., Li, J., Ye, W.-W. and Liu, S.-M. (2018) Dissolved methane in the East China Sea: Distribution, seasonal variation and emission. Marine Chemistry, 202 . pp. 12-26. DOI 10.1016/j.marchem.2018.03.001.

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Abstract

We present a dataset of dissolved methane (CH4) in the East China Sea (ECS) during five cruises in March, May, August, October and December 2011. CH4 distribution in this region showed pronounced spatial and seasonal variability due to the complex mixing of different water masses and other variables. Surface CH4 concentrations gradually decreased from the coast to the open sea, with maximum values occurring near Changjiang estuary or outside the Hangzhou Bay. The annual mean CH4 concentration of the surface layer was 9.1 ± 1.6 nmol L-1 in the coastal area, which was nearly twice as large as that in the open sea (4.3 ± 1.3 nmol L-1). CH4 was distributed evenly from the surface to the bottom in the shelf region during March and December, while it increased gradually with depth during May and October. CH4 depth profiles exhibited various distribution features along the coast, in the middle and on the edge of continental shelf. CH4 levels at the bottom were generally higher than at the surface during all seasons, indicating obvious CH4 sources from sediments. Incubation experiments of sediment cores onboard suggested that sediment release was an important source of CH4 in the water column of the ECS. We estimated that the annual average CH4 release rate from sediments was about 1.11 μmol·m-2·d-1 on the continental shelf of the ECS. The maximum CH4 concentration and sediment-water CH4 flux both occurred in summer, which might be related with the occurrence of hypoxia in the bottom water. Surface seawater of the ECS was oversaturated with CH4 relative to the atmosphere over most of the five cruises, indicating that the ECS was a net source of atmospheric CH4. The annual mean area-weighted sea-air flux density of CH4 in the ECS was estimated to be about 10.7 μmol·m-2·d-1 in 2011. Accordingly, an area-weighted, seasonally adjusted annual rate of CH4 efflux was determined to be 2.98 × 109 mol yr-1 (∼0.05 Tg CH4 yr-1) from the ECS to the atmosphere.

Document Type: Article
Keywords: Greenhouse gas; Dissolved methane; Seasonal variations; Gas exchange; East China Sea
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Refereed: Yes
Open Access Journal?: No
Publisher: Elsevier
Date Deposited: 19 Mar 2018 08:47
Last Modified: 08 Feb 2021 07:40
URI: https://oceanrep.geomar.de/id/eprint/42280

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