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

3. Seepage features in Irish Waters
Recent discoveries:
• Malin Sea pockmarks – 2003
(Monteys, 2008, Szpak, 2012)
• Dunmanus Bay pockmarks – 2007
(CE07_02, CV09_23, CE11_017)
• Irish Sea
– Lambay Deep mud diapir -
1998
– Codling Fault MDAC mounds -
2001
– Irish Sea pockmarks - 2009
(Croker, 2005, Judd 2007
CV09_26, CV10_28)
Malin Sea pockmarks
Codling Fault
MDAC mounds
Irish Sea pockmarks
Dunmanus Bay pockmarks
N
40km
Lambay Deep mud diapir

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

6. Malin Clone Libraries dominated by
hydrocarbon-degrading bacteria
Psychrobactersp.
Sulfitobactersp.
Alcanivoraxborkumensis SK2
Uncultured actinobacterium
clone ANTXXIII_706-4_Bac69
Pseudoalteromonas sp. P29
Uncultured propane-utilizing
bacterium (SIP20-4-09)
Colwelliasp.
Oil contaminated polar & Arabian marine settings
(Deppe, 2005, Giudice 2010, Radwan, 2007, 2010)
Oil contaminated polar sediments & beach sands
(Kostka, 2011 Guibert, 2012)
Hydrocarbon-degrader, often dominant in oil spills
(Yakimov, 1998)
Cold Seep, Weddell Sea, Antarctica (Niemann, 2009)
Crude oil contaminated Arctic sediments
(Deppe, 2005, Lin, 2009)
Hydrocarbon seeps, off Santa Barbara (Redmond, 2010)
Deepwater Horizon oil spill (Redmond, 2011, Baelum, 2012)
SettingClosest OrganismLibrary
40 – 59%
18 – 37%
0-7%
2 – 5%
3 – 4%
1.5 - 2%
0 – 2%

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

8. Codling Fault MDAC mounds
25cm 2cm
Actively seeping mound Pavement stacking Anoxic surface sediment
Carbonate & pyrite encrusted quartz grain Microbial structures Fluid flow pores

9. Codling Fault MDAC Mounds
m/z 205
MAGEPLFA
16:0
16:1
14:0
i-15:0
17:0 18:0
18:1
16:016:1ω7
14:0
ai15:0
15:0
18:1ω9
18:2
18:0
Archaeal DGGE
15:0
17:0
10Me16:0
ai-15:0
i15:0
br16:0
• Diagnostic PLFA’s and mono-alkyl glyceryl ethers
(MAGE) for AOM-associated sulphate reducing
bacteria abundant.
(Hinrichs, 2000, Pancost, 2001, Elvert, 2003, Niemann, 2008)
• DGGE indicates distinct archaeal community present
16:1ω5

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

11. Acoustic turbidity
2009 sampling
2011 sampling
Acoustic turbidity
N
Dunmanus Bay pockmarks
6m vibrocores
30m

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)

14. Acknowledgements
Xavier Monteys (GSI)Paul Flanagan (QUB)Anna Kulakov (QUB)
Michal Szpak (DCU)INFOMARMarine InstituteIRCSET
Geological Survey of Ireland