Quantitative analysis of mini-mounds from the Explorer and Dangeard canyons area: an automated approach

Stewart, Heather; Gafeira , Joana. 2016 Quantitative analysis of mini-mounds from the Explorer and Dangeard canyons area: an automated approach. [Poster] In: Marine Geological and Biological Habitat Mapping (GeoHab) 15th International Symposium, Winchester, UK, 2-6 May 2016. British Geological Survey.

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The Dangeard and Explorer canyons are located on the Celtic Margin, offshore UK, and are tributaries to the Celtic deep-sea fan via the Whittard Canyon. The heads of the Dangeard and Explorer canyons were surveyed during the MESH canyons cruise in 2007. Two previously unknown provinces of cold-water coral mini-mounds were discovered on the interfluves of these canyons (Stewart et al., 2014) and observed to comprise coral rubble and associated fauna including ophiuroids and the squat lobster Munida sarsi (Davies et al., 2014). In this paper we show results from the application of an automated mapping method to morphologically characterise these mini-mounds. The method employed was initially developed to map and characterise fluid-escape pockmarks at seabed (Gafeira et al., 2012), and was subsequently tailored to delineate positive topographic features such as mounds and compiled into an ArcGIS Tool Box (BGS Coral Mound Tools). This toolbox comprise two scripts that allow the systematic application of a sequence of tools available in ArcGIS and can be used to recognise, spatially delineate and characterise morphometrically seabed mounds using a Bathymetric Positioning Index (BPI) raster derived from the multibeam echosounder data. This time-efficient approach provides an unbiased and accurate mapping methodology, and through morphometric analysis, enables quantitative analyses of potentially vast numbers of seabed features. Multibeam bathymetry data were gridded at 5m cell size to generate a fine-scale BPI raster using the Benthic Terrain Modeler extension for ArcGIS (Wright et al., 2005). The first script generates an output polygon shapefile delineating the mini-mounds. The second script captures the morphological characteristics of each mound and populates the attribute table of the delineated polygons. Two other point shapefiles are also generated: 1) showing the centroid, and 2) marking the shallowest point, of each delineated mound. The outputs from the automated process reveal more than 2000 mini-mounds present in the Dangeard mini-mound province and more than 800 in the Explorer mini-mound province, representing a significant increase on previous estimates of mini-mounds in the area (Stewart et al., 2014). Morphometric data show that the mini-mounds of the Dangeard province are larger (3-4m high and up to 3.5km2 in area) than those observed in the Explorer province (2.5-3.5m high and up to 2km2 in area). While further work will be required to explain this phenomenon, it may reflect trawling damage within the Explorer province. The morphometric data also reveal that the mounds are elongated along slope, likely due to the influence of contour currents. Davies et al. 2014. Deep-Sea Research II, 104, 208-229 Gafeira et al. 2012. Near Surface Geophysics 10(4), 303-314 Stewart et al. 2014. Deep-Sea Research II, 104, 230-244 Wright et al. 2005.

Item Type: Publication - Conference Item (Poster)
Additional Keywords: cold-water coral mounds; carbonate mounds, multibeam echosounder
NORA Subject Terms: Earth Sciences
Marine Sciences
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Date made live: 29 Apr 2016 08:15 +0 (UTC)

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