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Discovery of a natural CO2 seep in the German North Sea: Implications for shallow dissolved gas and seep detection

Published inJournal of geophysical research, vol. 116, no. C3
Publication date2011
Abstract

A natural carbon dioxide (CO 2) seep was discovered during an expedition to the southern German North Sea (October 2008). Elevated CO 2 levels of ∼10–20 times above background were detected in seawater above a natural salt dome ∼30 km north of the East‐Frisian Island Juist. A single elevated value 53 times higher than background was measured, indicating a possible CO 2 point source from the seafloor. Measured pH values of around 6.8 support modeled pH values for the observed high CO 2 concentration. These results are presented in the context of CO 2 seepage detection, in light of proposed subsurface CO 2 sequestering and growing concern of ocean acidification. We explore the boundary conditions of CO 2 bubble and plume seepage and potential flux paths to the atmosphere. Shallow bubble release experiments conducted in a lake combined with discrete‐bubble modeling suggest that shallow CO 2 outgassing will be difficult to detect as bubbles dissolve very rapidly (within meters). Bubble‐plume modeling further shows that a CO 2 plume will lose buoyancy quickly because of rapid bubble dissolution while the newly CO 2 ‐enriched water tends to sink toward the seabed. Results suggest that released CO 2 will tend to stay near the bottom in shallow systems (<200 m) and will vent to the atmosphere only during deep water convection (water column turnover). While isotope signatures point to a biogenic source, the exact origin is inconclusive because of dilution. This site could serve as a natural laboratory to further study the effects of carbon sequestration below the seafloor.

Affiliation Not a UNIGE publication
Citation (ISO format)
MCGINNIS, Daniel Frank et al. Discovery of a natural CO<sub>2</sub> seep in the German North Sea: Implications for shallow dissolved gas and seep detection. In: Journal of geophysical research, 2011, vol. 116, n° C3. doi: 10.1029/2010JC006557
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ISSN of the journal0148-0227
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