Data from the inter-comparison of the spatial distribution of methane in the water column from seafloor emissions at two sites in the Western Black Sea, using a multi-technique approach

Date 2019-04
Temporal extent 2019-04-03 -2019-04-07
Author(s) Grilli RobertoORCID1, Birot Dominique2, Schumacher Mia3, Paris Jean-Daniel4, Blouzon Camille1, Donval Jean-Pierre2, Leau Helene2, Giunta Thomas2, Delmotte Marc4, Radulescu Vlad5, Balan Sorin5, 6, Greinert Jens3, Ruffine LivioORCID2
Affiliation(s) 1 : CNRS, Univ Grenoble Alpes, IRD, Grenoble INP, Grenoble, France
2 : Département Ressources Physiques et Ecosystèmes de Fond de Mer (REM), IFREMER, Plouzané, France
3 : GEOMAR Helmholtz Centre for Ocean Research, Kiel, Germany
4 : Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
5 : National Institute of Marine Geology and Geoecology–GeoEcoMar, Bucharest, Romania,
6 : Faculty of Geology and Geophysics, Doctoral School of Geology, University of Bucharest, Bucharest, Romania
DOI 10.17882/85836
Publisher SEANOE
Keyword(s) dissolved gas, methane, black sea, in situ measurements, gas seepages, instrumental inter-comparison
Abstract

Understanding the dynamics and fate of methane (CH4) release from oceanic seepages on margins and shelves into the water column, and quantifying the budget of its total discharge at different spatial and temporal scales, currently represents a major scientific undertaking. Previous works on the fate of methane escaping from the seafloor underlined the challenge in both, estimating its concentration distribution and identifying gradients.

In April 2019, the Envri Methane Cruise has been conducted onboard the R/V Mare Nigrum in the Western Black Sea to investigate two shallow methane seep sites at ∼120 m and ∼55 m water depth. Dissolved CH4 measurements were conducted with two continuous in-situ sensors: a membrane inlet laser spectrometer (MILS) and a commercial methane sensor (METS) from Franatech GmbH. Additionally, discrete water samples were collected from CTD-Rosette deployment and standard laboratory methane analysis was performed by gas chromatography coupled with either purge-and-trap or headspace techniques.

The resulting vertical profiles (from both in situ and discrete water sample measurements) of dissolved methane concentration follow an expected exponential dissolution function at both sites. At the deeper site, high dissolved methane concentrations are detected up to ∼45 m from the seabed, while at the sea surface dissolved methane was in equilibrium with the atmospheric concentration. At the shallower site, sea surface CH4 concentrations were four times higher than the expected equilibrium value. Our results seem to support that methane may be transferred from the sea to the atmosphere, depending on local water depths.

In accordance with previous studies, the shallower the water, the more likely is a sea-to-atmosphere transport of methane. High spatial resolution surface data also support this hypothesis. Well localized methane enriched waters were found near the surface at both sites, but their locations appear to be decoupled with the ones of the seafloor seepages. This highlights the need of better understanding the processes responsible for the transport and transformation of the dissolved methane in the water column, especially in stratified water masses like in the Black Sea.

© DOI: 10.3389/feart.2021.626372

Licence CC-BY-NC
Acknowledgements The research leading to these results has received funding from the ENVRIPlusH2020 project (call 597 Environment, project number 654182) the European Community’s Seventh Framework Programme 598 ERC-2015-PoC under grant agreement no. 713619 (ERC OCEAN-IDs) and from the Agence 599 Nationale de la Recherche (ANR) under grant agreement ANR-18-CE04-0003-01. The authors would like to thank all members of the team who took part in the cruise, colleagues from INGV-Palermo for their fruitful discussions and exchanges during the cruise, the captain and staff of the R/V Mare Nigrum and all the logistic support from the Romanian GeoEcoMar
Sensor metadata

A fast response membrane inlet laser spectrometer (MILS) prototype (t90 < 30 s, Grilli et al., 2018) and a commercial Franatech METS sensor were used. Data from laboratory analysis by Purgeand-trap (PT) and head-space (HS) technique on water samples are also reported.

Data
File Size Format Processing Access
Data from the MILS and MET sensor during the atmopsheric near-surface profile HP01 5 MB ASC Processed data Open access
Data from the MILS sensor during the atmopsheric near-surface profile HP03 1 MB ASC Processed data Open access
Data from the MILS sensor during the horizontal near-surface profile HP04 197 KB ASC Processed data Open access
Data from the MILS sensor during the horizontal near-surface profile HP05 323 KB ASC Processed data Open access
Data from the MILS sensor during the horizontal near-surface profile HP06 4 MB ASC Processed data Open access
Data from the MILS sensor during the vertical profile VP01 163 KB ASC Processed data Open access
Data from the MILS sensor during the vertical profile VP02 1 MB ASC Processed data Open access
Data from the MILS sensor during the vertical profile VP03 260 KB ASC Processed data Open access
Data from the MILS sensor during the vertical profile VP04 312 KB ASC Processed data Open access
Data from the MILS sensor during the vertical profile VP05 750 KB ASC Processed data Open access
Data from the discrete measurements using PT and HS techniques on the hydrocast HY02 475 bytes ASC Processed data Open access
Data from the discrete measurements using PT and HS techniques on the hydrocast HY04 424 bytes ASC Processed data Open access
Data from the discrete measurements using PT and HS techniques on the hydrocast HY05 450 bytes ASC Processed data Open access
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How to cite 

Grilli Roberto, Birot Dominique, Schumacher Mia, Paris Jean-Daniel, Blouzon Camille, Donval Jean-Pierre, Leau Helene, Giunta Thomas, Delmotte Marc, Radulescu Vlad, Balan Sorin, Greinert Jens, Ruffine Livio (2019). Data from the inter-comparison of the spatial distribution of methane in the water column from seafloor emissions at two sites in the Western Black Sea, using a multi-technique approach. SEANOE. https://doi.org/10.17882/85836