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).

Autor: Idczak J; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland., Brodecka-Goluch A; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland. Electronic address: aleksandra.brodecka-goluch@ug.edu.pl., Łukawska-Matuszewska K; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland., Graca B; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland., Gorska N; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland., Klusek Z; Institute of Oceanology, Polish Academy of Sciences, Powstanców Warszawy 55, 81-712 Sopot, Poland., Pezacki PD; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland., Bolałek J; Faculty of Oceanography and Geography, Institute of Oceanography, University of Gdańsk, Al. Marszałka Piłsudskiego 46, 81-378 Gdynia, Poland.
Jazyk: angličtina
Zdroj: The Science of the total environment [Sci Total Environ] 2020 Nov 10; Vol. 742, pp. 140306. Date of Electronic Publication: 2020 Jun 18.
DOI: 10.1016/j.scitotenv.2020.140306
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 (CH 4 , Cl - , Br - , F - , SO 4 2- , Ca 2+ , Mg 2+ , K + , Na + , ∑H 2 S, dP, dSi, NH 4 + , DIC, DOC) and microbiological analysis of sediments (16S rRNA) were performed. The content of CH 4 and CO 2 in the outflowing gas and its origin (δ 13 C-CH 4 and δ 2 D-CH 4 ) 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 CH 4 , 17.6% of CO 2 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.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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