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Pockmark morphological attributes at the Aquitaine slope, GAZCOGNE1 (2013) and BOBGEO2 (2010) marine expeditions

Pockmarks are defined as depressions on the seabed and are usually formed by fluid expulsions. Recently discovered, pockmarks along the Aquitaine slope within the French EEZ, were manually mapped although two semi-automated methods were tested without convincing results. In order to potentially highlight different groups and possibly discriminate the nature of the fluids involved in their formation and evolution, a morphological study was conducted, mainly based on multibeam data and in particular bathymetry from the marine expedition GAZCOGNE1, 2013. Bathymetry and seafloor backscatter data, covering more than 3200 km², were acquired with the Kongsberg EM302 ship-borne multibeam echosounder of the R/V Le Suroît at a speed of ~8 knots, operated at a frequency of 30 kHz and calibrated with ©Sippican shots. Precision of seafloor backscatter amplitude is +/- 1 dB. Multibeam data, processed using Caraibes (©IFREMER), were gridded at 15x15 m and down to 10x10 m cells, for bathymetry and seafloor backscatter, respectively. The present table includes 11 morphological attributes extracted from a Geographical Information System project (Mercator 44°N conserved latitude in WGS84 Datum) and additional parameters related to seafloor backscatter amplitudes. Pockmark occurrence with regards to the different morphological domains is derived from a morphological analysis manually performed and based on GAZCOGNE1 and BOBGEO2 bathymetric datasets.

The pockmark area and its perimeter were calculated with the “Calculate Geometry” tool of Arcmap 10.2 (©ESRI) (https://desktop.arcgis.com/en/arcmap/10.3/manage-data/tables/calculating-area-length-and-other-geometric-properties.htm). A first method to calculate pockmark internal depth developed by Gafeira et al. was tested (Gafeira J, Long D, Diaz-Doce D (2012) Semi-automated characterisation of seabed pockmarks in the central North Sea. Near Surface Geophysics 10 (4):303-315, doi:10.3997/1873-0604.2012018). This method is based on the “Fill” function from the Hydrology toolset in Spatial Analyst Toolbox Arcmap 10.2 (©ESRI), (https://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/fill.htm) which fills the closed depressions. The difference between filled bathymetry and initial bathymetry produces a raster grid only highlighting filled depressions. Thus, only the maximum filling values which correspond to the internal depths at the apex of the pockmark were extracted. For the second method, the internal pockmark depth was calculated with the difference between minimum and maximum bathymetry within the pockmark.

Latitude and longitude of the pockmark centroid, minor and major axis lengths and major axis direction of the pockmarks were calculated inside each depression with the “Zonal Geometry as Table” tool from Spatial Analyst Toolbox in ArcGIS 10.2 (©ESRI) (https://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/zonal-statistics.htm). Pockmark elongation was calculated as the ratio between the major and minor axis length.

Cell count is the number of cells used inside each pockmark to calculate statistics (https://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/zonal-geometry.htm). Cell count and minimum, maximum and mean bathymetry, slope and seafloor backscatter values were calculated within each pockmark with “Zonal Statistics as Table” tool from Spatial Analyst Toolbox in ArcGIS 10.2 (©ESRI). Slope was calculated from bathymetry with “Slope” function from Spatial Analyst Toolbox in ArcGIS 10.2 (©ESRI) and preserves its 15 m grid size (https://pro.arcgis.com/en/pro-app/tool-reference/spatial-analyst/slope.htm). Seafloor backscatter amplitudes (minimum, maximum and mean values) of the surrounding sediments were calculated within a 100 m buffer around the pockmark rim.

 
Citation proposal
MICHEL Guillaume (IFREMER, Unité Géosciences Marines, France) - DUPRE Stephanie (IFREMER, Unité Géosciences Marines, France) - SAOUT Johan (IFREMER, Unité Géosciences Marines, France) - EHRHOLD Axel (IFREMER, Unité Géosciences Marines, France) - GUERIN Charline (IFREMER, Unité Géosciences Marines, France) - GAUTIER Emeric (IFREMER, Unité Géosciences Marines, France) - BRETON Cecile (E.C.C.O, Maison-Alfort, France) - BOURILLET Jean-Francois (IFREMER, Unité Géosciences Marines, France) - LOUBRIEU Benoit (IFREMER, Unité Géosciences Marines, France) (2017) . Pockmark morphological attributes at the Aquitaine slope, GAZCOGNE1 (2013) and BOBGEO2 (2010) marine expeditions. https://services.mspdata.eu:/geonetwork/srv/api/records/seanoe:48323

Simple

Date ( Publication )
2017-02-16
Date ( Revision )
2021-05-12
Other citation details
Michel Guillaume, Dupre Stephanie, Saout Johan, Ehrhold Axel, Guerin Charline, Gautier Emeric, Breton Cecile, Bourillet Jean-Francois, Loubrieu Benoit (2017). Pockmark morphological attributes at the Aquitaine slope, GAZCOGNE1 (2013) and BOBGEO2 (2010) marine expeditions. SEANOE. https://doi.org/10.17882/48323
Credit
The GAZCOGNE study as well as the marine expedition GAZCOGNE1 were co-funded by TOTAL and IFREMER as part of the PAMELA (Passive Margin Exploration Laboratories) scientific project (http://dx.doi.org/10.18142/236). The BOBGEO2 marine expedition was part of the FP7 EU Project CORALFISH.

  Author

IFREMER, Unité Géosciences Marines, France - MICHEL Guillaume  

  Author

IFREMER, Unité Géosciences Marines, France - DUPRE Stephanie  

  Author

IFREMER, Unité Géosciences Marines, France - SAOUT Johan  

  Author

IFREMER, Unité Géosciences Marines, France - EHRHOLD Axel  

  Author

IFREMER, Unité Géosciences Marines, France - GUERIN Charline  

  Author

IFREMER, Unité Géosciences Marines, France - GAUTIER Emeric  

  Author

E.C.C.O, Maison-Alfort, France - BRETON Cecile  

  Author

IFREMER, Unité Géosciences Marines, France - BOURILLET Jean-Francois  

  Author

IFREMER, Unité Géosciences Marines, France - LOUBRIEU Benoit  

  Publisher

SEANOE  
Keywords ( Theme )
  • pockmark , morphology , seafloor , bathymetry , backscatter , GIS , Marine geology , Physical oceanography
Keywords ( project )
  • FP7 CORALFISH (Agreement: 213144)
ODATIS aggregation parameters and Essential Variable names ( Theme )
  • Bathymetry
SeaDataNet Parameter Disciplines ( parameter )
  • Marine geology , Physical oceanography
Type de jeux de donnée ODATIS ( Theme )
  • Analysis data
Use constraints
Other restrictions
Other constraints
Date ( Publication )
2017

  Publisher

Elsevier BV  

  Author

MICHEL GUILLAUME  

  Author

DUPRE STEPHANIE  

  Author

BALTZER AGNES  

  Author

EHRHOLD AXEL  

  Author

IMBERT PATRICE  

  Author

PITEL MATHILDE  

  Author

LOUBRIEU BENOIT  

  Author

SCALABRIN CARLA  

  Author

LAZURE PASCAL  

  Author

MARIE LOUIS  

  Author

GELDOF JEAN-BAPTISTE  

  Author

DEVILLE ERIC  
Association Type
Cross reference
Initiative Type
document
Association Type
Cross reference
Initiative Type
Platform
Association Type
Cross reference
Initiative Type
Platform
Metadata language
English
Topic category
  • Oceans
N
S
E
W


Distribution format
  • CSV ( )

OnLine resource
Quality controlled data  
OnLine resource
DOI of the product  
OnLine resource
Seanoe  
Hierarchy level
Dataset
Statement

Metadata

File identifier
seanoe:48323   XML
Metadata language
English
Character set
UTF8
Hierarchy level
Dataset
Date stamp
2021-05-12
Metadata standard name
ISO 19115:2003/19139
Metadata standard version
1.0

  Point of contact

IFREMER, Unité Géosciences Marines, France - MICHEL Guillaume  
 
 

  Overviews

Shaded bathymetric map (15 m grid resolution) along the Aquitaine slope exhibiting pockmarks (GAZCOGNE1 marine expedition, 2013).

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