New seabed geological map of the Porcupine Bank & seabed ...

Seabed geology and
geomorphology of the
Porcupine Bank
Xavier Monteys & Ronan O’Toole (GSI)
INFOMAR

Acknowledgments
• David Hardy & Charise McKeon (GSI)
• Silvia Caloca (GSI)
• Glenn Nolan & MI oceanographic team
• Colm Lordan (MI)
• Eimear O'Keeffe (MI)
• Peter Croker (PAD)
• Anthony Grehan (NUIG)
• Shipboard party of a number of expeditions from 2000 to 2010

Outline
• Background
– The backbones: INSS, INFOMAR,…
– Large-scale deep-water issues
• Physical seabed characterization
– Objectives & Strategy
– Challenges
– Setting
• Results
– Geomorphological maps
– Seabed sediment type maps
• Discussion & Conclusions

The skeleton
Billions & Billions of Deep Echoes
RT
PB
IRELA ND
PR
P
WEST PORCUPINE
P: PORCUPINE BASIN
PB: PORCUPINE BANK
PR: PORCUPINE RIDGE
RT: ROCKALL TROUGH

Goals
Top objective: to develop a comprehensive
Physical Seabed Geo-database for the
Porcupine Bank for multidisciplinary
applications.
1. From acoustic properties to seabed sed. classes
2. Derive geomorphological features from acoustic
datasets
3. Ground-truth & characterize the Geo-database

Data challenges
• Pros:
– Consistency:1 ship, 1
system, short survey time
– Survey Planning
MBES
EM 1002 95 kHz
• Cons:
–System settings (2)
–Different years (2)
–Depth range (scales)
–Scattering domains
–The weather! (QC)
10-25m
Penetration: 0-~m
SBP

Ocean

Geology
Modified from Haughton et al, 2005
E–W cross section of the Porcupine Basin (modified from Ziegler 1982 & VanRenbsergen 2007 )

Recent environment (~LGM)
After Sejrup et al,. 2005

Seabed
Indurated clay-sand
contourites

Geomorphology

Iceberg Keel marks
Track
7.6Km Long
250-300m wide
10-12m deep
Berms: 1-2m

Overview: Bedrock

Overview: Mounds

Overview:Ridges

Overview: Escarpments

Overview: Iceberg
keelmarks

From the raw backscatter data…

…To the Seabed Geology
G Cl Lit
ho
Coarse Medium
A 1 sG
2 sG
3 sG
B 4 S
5 S
C 6 mS
fines
7 sM
8 M
9 M
10 M

Seabed geology
G Cl Litho
Coarse Medium
A 1 sG
2 sG
3 sG
B 4 S
5 S

B
C 6 mS
7 sM
fines
8 M
9 M
10 M

Summary
• Seabed and geomorphological maps have been produced
and disseminated in a public geodatabase for a range of
multidisciplinary applications (e.g. site survey, nephrops,…)
• Multiapproach backscatter processing strategy key to obtain
good discrimination between sediment classes and to explore
variability within each class
• Statistical analysis show good correlation patterns between
backscatter levels and sediment properties
– Backscatter analysis discriminates a large number of soft fine-grained seabed
types on the slopes, 250-500m (good correlation with % sand)
– But not as good discriminator on hard seabeds (and not grain size correlated)
• Interpretation of lineaments suggests a more complex glacial history of the
Bank

•Future work: Porcupine Bank expedition in 2011?
After Sejrup et al,. 2005