Open AccessDiscovery of a natural CO 2 seep in the German North Sea: Implications for shallow dissolved gas and seep detection
Author(s) -
McGinnis Daniel F.,
Schmidt Mark,
DelSontro Tonya,
Themann Sören,
Rovelli Lorenzo,
Reitz Anja,
Linke Peter
Publication year - 2011
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jc006557
Subject(s) - petroleum seep , plume , seafloor spreading , seawater , geology , sink (geography) , oceanography , carbon dioxide , atmosphere (unit) , context (archaeology) , salt dome , flux (metallurgy) , methane , geochemistry , meteorology , chemistry , paleontology , geography , physics , cartography , organic chemistry
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.