|Titre||The Banquereau surf clam dredging impact study "ten years after" and seabed photography
of Laurentian Channel: Technical Report on the CCGS Hudson Cruise 2008-015, First Leg. Fisheries and Oceans Canada (DFO) and the Geological Survey of Canada - Atlantic (GSC-A) June 10-14, 2008|
|Auteur||King, E L; Atkinson, A|
|Source||Commission géologique du Canada, Dossier public 5911, 2013, 61 pages, https://doi.org/10.4095/292591 (Accès ouvert)|
|Éditeur||Ressources naturelles Canada|
|Media||en ligne; numérique|
|Province||Région extracotière de l'est|
|Lat/Long OENS|| -58.0250 -57.8583 44.5000 44.4167|
|Sujets||levés sismiques; sonar latéral; levés acoustiques; bathymétrie; topographie du fond océanique; topographie du fond océanique; dragage; dragage en mer profonde; trous; boues; tills; peuplements
biologiques; dépôts glaciaires; topographie glaciaire; géophysique; géologie marine; Cénozoïque; Quaternaire|
|Illustrations||location maps; tables|
|Programme||Aléas géologiques et contraintes à la mise en valeur des ressources extracôtières, Géosciences à l'appui de la gestion des océans|
|Diffusé||2013 05 28|
|Résumé||(Sommaire disponible en anglais seulement)|
Leg 1 of DFO Hudson Cruise 2008015 was conducted from June 10 to 14 on Banquereau and the outer Laurentian Channel. A joint DFO (Department of
Fisheries and Oceans) and NRCan-GSCA (Natural Resources Canada, Geological Survey of Canada) expedition included a resurvey of the DFO Dredge Impact Study area on outer Banquereau, Scotian Shelf, using sidescan sonar, to assess the nature of
long-lived dredge tracks 10 years after their creation, followed by seabed photography in Laurentian Channel.
The Banquereau site had changed significantly by the tenth year following 5 years of less significant change. Bedforms, mainly 3-D
megaripples from storm event(s) have modified most dredges so as to be invisible. A seabed features map has been compiled.
At three sites in the Laurentian Channel seabed video, still photography and limited sampling was used to assess the nature
of the seabed which gives rise to high backscattering on sidescan sonograms (from 2006 and 2007) on mud in pockmarked and iceberg soured areas. A long video transect across mud of highly variable local thickness (0-10 m) at the outer Laurentian
Channel showed Holocene age muds cover a relict iceberg scoured till which outcrops only locally, exposing gravel and cobbles with attached biota. A thin (cm) mud dusting is apparently penetrated by the sidescan sonograms to register a high
backscatter return, thus under-representing the extent of the very thin mud. The properties of the backscattering medium which give rise to small circular patches at the base of small pockmarks remains uncertain.
A long videograb transect across
scattered pockmarks on the east flank of Laurentian Channel failed to indicate the nature of strong central backscattering ("eyed pockmarks") in thick muds. This suggests that the ubiquitous dusting of nepheloid layer (brownish mud up to several cm
in the grab samples) covers the backscattering targets. It suggests little or no recent gas escape activity.
A long video and still transect across the Scaterie Moraine to substantiate anecdotal reports of the coral Lophelia and to observe seabed
stability demonstrated varied biota and a large sponge community and no apparent modern retrogressive mass sediment failure on early post-glacial slump scars.