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TitreA belt of seabed erosion along the Beaufort Sea margin governed by Holocene evolution of the Beaufort shelf-break jet: geological evidence, current measurements and initial oceanographic modelling
AuteurKing, E L; Li, M Z; Wu, Y; Forest, A; Blasco, S; Harrison, P; Melling, H; Dallimore, S; Paull, C; Cameron, G
SourceArcticNet, abstracts, 2016 Annual Scientific Meeting - Réunion scientifique annuelle; 2016, 114-115 pages
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160301
RéunionArcticNet 2016 Annual Scientific Meeting - Réunion scientifique annuelle; Winnipeg, MB; CA; décembre 5-12, 2016
Mediaen ligne; numérique
ProvinceRégion extracotière du nord
Sujetsbathymétrie; sediments; érosion; sedimentation; sedimentation; trajectoires d'écoulement
ProgrammeRisques géo marines, Géoscience pour la sécurité publique
LiensOnline - En ligne (complete volume - volume complet, PDF, 1585 KB)
Résumé(disponible en anglais seulement)
Evidence from seabed geological observations, in situ oceanographic measurements and initial oceanographic modelling converge to indicate that the Beaufort shelf-break jet (BSJ) and related process amplifications are responsible for generating an observed shelf break erosional belt. A narrow (1-8km wide) belt cut several metres into muds that were derived from the Mackenzie Delta. This belt extends 250km along the uppermost slope and shelf break in water depths from 80 0150250m. The surface is generally smooth and planar except where post- or syn-deformation by pingo-like features (PLFs) structurally disrupt the seabed. The erosion belt is flanked by both non-depositional and depositional zones. Other seabed indicators of the current are lee-side mud depocentres (possibly comet marks) on the PLFs detected in autonomous underwater vehicle-based multibeam sonar (1m resolution) and elongated pockmarks. Recent compilation of C14 dates from shells and foraminifera in sediment cores are correlated to seismic horizons and mapped across the upper slope. These demonstrate that strata from about 11 ka until ~8 ka, before present (cal.) maintain a uniformly draped blanket deposit, but by 5 ka the blanket is more affected by currents. After this time, these and underlying strata were truncated (eroded) at the uppermost slope, with removal of several metres of sediment. Adjacent non-deposition (bypass) zones give way to local deposition, presently maintained. The patterns and erosion age constrain the genesis to oceanographic phenomena (sea-level low-stand and glacial flooding genesis would have to be earlier). This demonstrates a mid-Holocene change in mud distribution and an evolution of currents capable of the erosion. ArcticNet and DFO moorings demonstrate episodic year-round strong current and sediment re-suspension events attributed to amplifications of the BSJ that flows trapped to the upper slope. The associated current surges (20-80 cm/s) in the BSJ are primarily driven by longshore stress from storms causing upwelling and downwelling while additional processes on the shelf (e.g. wind-driven resuspension, thermohaline convection, eddy formation) add further complexity to our understanding of sediment transport dynamics in the region. Recent calculations show that sediment mobilization at the shelf break due to intensifications in the BSJ typically occurs ~3% of the time. An instrumented seabed lander in co-location with ArcticNet moorings was deployed for a year. Analyses of measured current and turbidity time series are pending. Initial 3-D, 12.5km resolution modelling efforts output daily mean temperature, salinity, velocity and other ocean and ice parameters. It was partially validated by in situ current data measured at 8m above the seabed. Eastward flow and occasional reversal, elements of up- and down-welling during storms, dense water cascading, meso-scale eddies due to fall and winter sea-ice formation and a sea-ice breakup event were generated by the model. Relative magnitude of modelled processes needs further investigation, but the first representations of the BSJ core between 40 and 100m water depth overlaps the erosion/ non-deposition zone. Thus, in-situ currents capable of mud re-suspension and the superposition of the modelled BSJ and associated amplifications roughly match the mud patterns. Age constraints indicate mid-Holocene BSJ evolution and continued maintenance of shelf break bypass.
Résumé(Résumé en langage clair et simple, non publié)
Les données acoustiques d'un profileur de sédiments nous permettent de reconnaître sur le fond marin des sédiments érodés de boues stratifiées pouvant mesurer plusieurs mètres, le long d'une étroite ceinture mesurant 1 à 8 km de largeur, à la rupture de pente du plateau de Beaufort. La présence d'une zone correspondante sans dépôt (contournement) a également été observée. La datation au radiocarbone des sédiments indique que l'érosion a commencé vers le milieu de l'Holocène, soit il y a environ 6000 ans. Des mouillages d'instruments océanographiques sur une longue période ont indiqué précédemment qu'il existe des courants périodiques capables de remettre des boues en suspension. Ces courants sont associés au jet de rupture du plateau de Beaufort (JRPB) et longent les courbes du plateau. Les premiers travaux de modélisation 3D ont mené à la reproduction fidèle du JRPB. Les méthodes utilisées pour la géologie, la chronologie, l'océanographie et la modélisation convergent et indiquent qu'une évolution ou une amplification du JRPB a eu lieu au milieu de l'Holocène.