A geophysical, geochemical and microbiological study of a newly discovered pockmark with active gas seepage and submarine groundwater discharge (MET1-BH, central Gulf of Gdańsk, southern Baltic Sea) - Publikacja - MOST Wiedzy

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A geophysical, geochemical and microbiological study of a newly discovered pockmark with active gas seepage and submarine groundwater discharge (MET1-BH, central Gulf of Gdańsk, southern Baltic Sea)

Abstrakt

High-resolution bathymetric data were collected with a multi-beam echosounder in the southern part of the Baltic Sea (region MET1, Gulf of Gdańsk) revealing the presence of a 10 m deep and 50 m in diameter pockmark (MET1-BH) on the sea bottom (78.7 m). To date, no such structures have been observed to reach this size in the Baltic Sea. The salinity of the near-bottom water in the pockmark was about 2 PSU (about 31.22 mmol/l Cl), which clearly indicated the presence of a submarine groundwater discharge (SGD). Water column, sediments and the seabed structure were investigated in the MET1-BH area using various hydroacoustic devices: multi-beam and splitbeam echosounders and a sub-bottom profiler. Geochemical analyses of sediment pore waters (CH4, Cl, Br, F, SO42−, Ca2+, Mg2+, K+, Na+, ∑H2S, dP, dSi, NH4+, DIC, DOC) and microbiological analysis of sediments (16S rRNA) were performed. The content of CH4 and CO2 in the outflowing gas and its origin (δ13C-CH4 and δ2D-CH4) were determined. Hydroacoustic data showed that gas was emitted intensively from the inside of the structure. The height and intensity of the gas flares varied depending on the hydrostatic pressure. The gas contained 76.1% of CH4, 17.6% of CO2 and 0.39% of He. Methane source was microbial. Geophysical investigation revealed the presence of dislocations in sub-surface sediment layers in the MET1 region, which could have created a passage for groundwater and gas. Geochemical analyses pointed to intensive processes of organic matter decomposition in this area, active methanogenesis in the surface sediment layer, lack of the sulphate-methane transition, and freshwater seepage at a depth of ~88 m (bottom of the pockmark), probably from Upper Cretaceous deposits. The Prokaryota composition, atypical for marine surface sediments, resulted from the combination of freshwater and high organic matter content, and reflected active in situ methanogensis.

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Informacje szczegółowe

Kategoria:
Publikacja w czasopiśmie
Typ:
Publikacja w czasopiśmie
Opublikowano w:
SCIENCE OF THE TOTAL ENVIRONMENT nr 742,
ISSN: 0048-9697
ISSN:
0048-9697
Rok wydania:
2020
DOI:
Cyfrowy identyfikator dokumentu elektronicznego (otwiera się w nowej karcie) 10.1016/j.scitotenv.2020.140306
Weryfikacja:
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