Publication Date:
2022-05-25
Description:
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q01011, doi:10.1029/2011GC003787.
Description:
Marine pockmarks are a specific type of seabed geological setting resembling craters or pits and are considered seabed surface expressions of fluid flow in the subsurface. A large composite pockmark on the Malin Shelf, off the northern coast of Ireland was surveyed and ground truthed to assess its activity and investigate fluid related processes in the subsurface. Geophysical (including acoustic and electromagnetic) data confirmed the subsurface presence of signatures typical of fluids within the sediment. Shallow seismic profiling revealed a large shallow gas pocket and typical gas related indicators such as acoustic blanking and enhanced reflectors present underneath and around the large pockmark. Sulphate profiles indicate that gas from the shallow reservoir has been migrating upwards, at least recently. However, there are no chimney structures observed in the sub-bottom data and the migration pathways are not apparent. Electromagnetic data show slightly elevated electrical conductivity on the edges of the pockmarks and a drop below regional levels within the confines of the pockmark, suggesting changes in physical properties of the sediment. Nuclear Magnetic Resonance (NMR) experiments were employed to characterize the organic component of sediments from selected depths. Very strong microbial signatures were evident in all NMR spectra but microbes outside the pockmark appear to be much more active than inside. These observations coincide with spikes in conductivity and the lateral gas bearing body suggesting that there is an increase in microbial activity and biomass when gas is present.
Description:
We wish to thank the Geological Survey of Ireland, the
INtegrated Mapping FOr the Sustainable Development of Ireland’s MArine Resource (INFOMAR) program, the Irish
Environmental Protection Agency, Science Foundation of
Ireland, QUESTOR (Queens University Belfast) and the Irish
Council for Science, engineering and technology for funding
this research. AJS thanks NSERC, (Strategic and Discovery
Programs), the Canada Foundation for Innovation (CFI), and
the Ministry of Research and Innovation (MRI) for providing
Canadian funding. The survey data utilized in the research has
been co‐funded by the Geological Survey of Ireland and the Offshore
Irish Petroleum Infrastructure Programme (PIP; Ref. No:
IS05/16 Malin Basin EM).
Description:
2012-07-19
Keywords:
Malin Shelf
;
NMR
;
Electromagnetic
;
Microbial
;
Organic matter
;
Pockmark
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
