Sediment transport on the eastern Canadian continental shelf

Abstract

A synthesis is presented of the sediment transport pathways resulting from hydrodynamic processes over the eastern Canadian continental shelf. This is based on interpretation of bedform type and orientation, grain size trends, sediment stratigraphy, visual observation and direct measurements. These pathways are then compared with results of numerical simulations of the transport of 0.35 mm (medium) sand for the Grand Banks of Newfoundland, the Scotian Shelf and the Gulf of Maine. The abundance of hydrodynamically reworked sediment increases from north to south. There is no evidence for sediment transport on the Baffin Shelf or Arctic Island Channels due largely to ice cover and deep (200 m) water. Sediment transport on the Labrador Shelf, by contrast, is apparent though restricted to bank tops in depths less than 120 m. This transport is predominantly to the southeast under the influence of strong wind-driven and geostrophic flows. The Grand Banks of Newfoundland is subject to storm-induced sand transport in depths less than 120 m. Transport here is to the south and southeast over much of Grand Bank and Avalon Channel. Above approximately 60 m the seabed is devoid of sand, suggesting scouring; between 60 and 120 m sand transport takes place principally as bedload. The shelf immediately south of Newfoundland is subject to strong easterly sediment transport that has scoured the banktops of all but gravel-sized sediment. The Scotian Shelf and Georges Bank also exhibit storm-induced sediment transport that is tidally-modulated in depths less than 100 m. The predicted and observed sand transport pathways are remarkably consistent. Predicted zones of sand convergence and divergence correspond to known regions of sand accumulation and depletion, respectively. Quantitative predictions are, by contrast, only within an order of magnitude of observations. Percentage exceedence predictions of sand transport for the Hibernia (Grand Banks of Newfoundland) and Venture (Sable Island Bank) discovery sites show strongly linear trends on a Gumbel distribution. These plots show that intense storms (greater than 20 year return interval) dominate net transport at Hibernia, whereas short-term storms (annual or shorter return interval) dominate at Venture.