British Organic Geochemistry Meeting 2012, Leeds University, Oral Presentation
1. Multidisciplinary Characterization of fluid
seepage features in Irish Waters
Shane O’ Reilly
Dr. Andre Simpson, Dr. Christopher Allen, Dr. Brian Kelleher
2. Seabed fluid seepage
What?
Subseabed migration of:
• Methane
• Higher hydrocarbons
• Pore water
• Groundwater
Importance?
• Global warming
• Unique biodiversity
• Petroleum & gas prospecting
• Marine industrial safety
• Formation of dramatic geological features
Bayon, 2009
i
1m
ii. Methane-derived authigenic carbonate
(MDAC) nodules and mounds
i. Pockmarks
- Seafloor depressions
- Most are dormant/low activity
ii
Seepage features
4. Malin Shelf pockmark
• Large composite pockmark, 180m water depth
• Located in isolated fine grained muddy sediments
• Located in region of gas and petroleum resource interest
• Seismic data indicates gas pocket at 20mbsf
• Geophysics and underwater video indicates currently dormant or
low activity feature
• Previous work (Szpak, 2012) lateral migration of gas around
crater and decreased activity within
5. Malin Pockmark Archaeal Diversity
-Mixed community present
-Known anaerobic
methanotrophic (ANME)
groups not dominant
- Suggests processes other
than AOM occuring
7. Codling Fault MDAC mounds
• 23 mounds along the Codling Fault Zone
• 250m long, 80m wide and 5-10m in relief
• Dynamic erosional setting
• Extensive areas covered by sand waves
Xavier Monteys, Geological Survey of Ireland
10. Western Irish Sea pockmarks
• >15 pockmarks mapped in 40 – 50m water depth
• Extensive regional sub-seabed gas signatures evident, not isolated at pockmarks
• Water column eco-facies indicate widespread but minor seepage to water column
• Video investigation - no MDAC, bacterial mats, seep-associated macrofauna
New pockmarks
Xavier Monteys, Geological Survey of Ireland
12. Dunmanus Bay pockmarks
Vicinity
Crater
Control
PO4
3- (μM)NH4
+ (mM)H2S(mM)SO4
2- (mM)Particle Size CH4(μM)
• Elevated CH4, H2S, PO4
3- and NH4
+ at and in vicinity of pockmark
• Evident lithological control on geochemical processes
• Greater activity in vicinity of craters suggests divergence of flow after formation
Sand
Sandy Mud
Mud
Gravel
13. Conclusions & Future Work
Extensive seepage features within Irish waters.
- Malin pockmark: Subsurface gas present but no water column
seepage recorded. Microbial populations indicate hydrocarbons other
than methane are significant.
- Irish Sea mudbelts: Subsurface gas present throughout region,
pockmarks currently low activity settings
- Codling Fault Mounds: An active seepage setting, distinct microbial
communities and evidence of anaerobic oxidation of methane.
- Dunmanus Bay pockmarks: Active but minor seepage. Lithological
controls on seepage and microbial processes evident.
Future work
Archaeal lipid biomarkers
Pyrosequencing (Dunmanus& Codling Fault)
Pore water and solid phaseNMR(Dunmanus)