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TitleA 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
AuthorKing, 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
LinksOnline - En ligne (complete volume - volume complet, PDF, 1585 KB)
Alt SeriesEarth Sciences Sector, Contribution Series 20160301
MeetingArcticNet 2016 Annual Scientific Meeting - Réunion scientifique annuelle; Winnipeg, MB; CA; December 5-12, 2016
Mediaon-line; digital
File formatpdf
ProvinceNorthern offshore region
AreaBeaufort Sea; Mackenzie continental slope
Subjectsbathymetry; sediments; erosion; deposition; sedimentation; flow trajectories; seabed geology; oceanographic modelling; seafloor features; uowelling; downwelling
ProgramMarine Geohazards, Public Safety Geoscience
AbstractEvidence 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.
Summary(Plain Language Summary, not published)
Erosion of up to several metres of stratified muds at the seabed is recognized from acoustic sub-bottom profiler data along a narrow belt, 1-8km wide, at the shelf-break of the Beaufort Shelf. A corresponding zone of non-deposition (bypass) is also observed. Dating of the sediments by radiocarbon methods indicates the erosion began in mid Holocene times, about 6000 years ago. Long-term oceanographic moorings have previously demonstrated periodic currents capable of mud re-suspension associated with the contour-parallel Beaufort Shelfbreak Jet (BSJ). Initial 3-D modelling efforts successfully replicate the BSJ. The geologic, chronologic, oceanographic and modelling approaches converge to indicate a mid-Holocene BSJ evolution and/or amplification.