| Title | Observation of internal tides and sediment transport processes at the head of Logan Canyon, central Scotian Slope, eastern Canada |
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| Author | Li, M ; Prescott,
R H; Robertson, A G |
| Source | 2018 Ocean Sciences Meeting, online scientific program; MG53A-05, 2018 p. 1 |
| Links | Online - En ligne
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| Image |  |
| Year | 2018 |
| Alt Series | Natural Resources Canada, Contribution Series 20170361 |
| Publisher | American Geophysical Union |
| Meeting | 2018 Ocean Sciences Meeting, American Geophysical Union; Portland, Oregon; US; February 11-16, 2018 |
| Document | book |
| Lang. | English |
| Media | on-line; digital |
| File format | html; pdf |
| Province | Nova Scotia; Eastern offshore region |
| NTS | 10 |
| Lat/Long WENS | -60.7167 -58.4167 43.7000 42.8167 |
| Subjects | marine geology; surficial geology/geomorphology; sedimentology; submarine canyons; marine sediments; sands; hydrodynamics; sediment transport; currents; tides; temperature; bed load; suspended load;
turbidity currents; Scotian Slope; Logan Canyon |
| Program | Public Safety
Geoscience Marine Geohazards |
| Released | 2018 02 01 |
| Abstract | An instrumented seabed lander was deployed in the head of Logan Canyon in summer 2005 to obtain the first observations of near-bed hydrodynamics and sediment transport processes in a canyon on the
glaciated Scotian Slope. The lander recorded strong up- and down-canyon current pulses that typically last 2-5 hours. The hour-averaged current speed in these pulses reaches 30-40 cm/s although the maximum instantaneous speed is up to 70 cm/s. The
current pulses are, however, asymmetric with quick build-up of the up-canyon pulses and more gradual reversal to down-canyon flows. The down-canyon pulses also have higher speeds and last longer than the up-canyon pulses to result in a mean
down-canyon velocity of ~4 cm/s. Temporal changes of the current pulses and their correlation with tidal elevation and the rise and fall of temperature suggest that the observed high-frequency strong current pules were internal tide bores formed due
to the focusing of tidal energy by the geometry of the canyon. The strong currents of the internal tidal bores caused frequent transport of the fine sand in the head of Logan Canyon. Bedload transport occurred in 2.1% of the time and suspended-load
in 1.2% of the time. In strong current events that caused suspended-load transport, suspended sediment concentrations were typically 5-10 mg/L above the background value but reached the maximum of ~70 mg/L. Based on the measured bottom currents and
near-bed suspended sediment concentration, the estimated maximum bedload transport was 0.003 g/cm/s while suspended-load transport was at least one order of magnitude higher and reached ~0.15 g/cm/s. The mean sediment transport flux averaged over the
deployment was ~7.4 x 10 g/cm/s in the down-canyon direction. The strong bottom currents of the internal tidal bores and the resultant intensive sediment transport could be a potential mechanism for sediment mobilization and turbidity current
formation in canyons on the Scotian Slope margin. |
| Summary | (Plain Language Summary, not published)
An instrumented seabed lander was deployed in the head of Logan Canyon in August 2005 to provide the first observations of near-bed currents and sediment
mobility in a canyon on the Scotian Slope. The lander data show strong up- and down-canyon current pulses that reach up to 70 cm/s and typically last 2-5 hours. Temporal changes of the current pulses and their correlation with tidal elevation and
temperature suggest that the observed high-frequency current pules were internal tide bores formed due to the focusing of tidal energy by the geometry of the canyon. The strong currents of the internal tidal bores caused frequent bedload and
suspended-load transport events in which maximum suspended sediment concentration reached ~100 mg/l. The strong bottom currents of the internal tidal bores and the resulting intensive sediment transport could be a potential mechanism for sediment
mobilization and turbidity current formation in canyons on the Scotian Slope margin. |
| GEOSCAN ID | 306616 |
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