Abstract

Elongate bedforms of less than one meter relief are abundant on the North Atlantic shelf floor. Spacing between features, and width of solitary forms, ranges from 15 to 50 m. Length-to-width ratios observed by side-scan sonar are in excess of 10:1. The most common form consists of a band of coarse sand or shelly gravel that is depressed slightly below the level of the finer sand on either side. In some cases these bedforms appear to be erosional windows exposing the basal coarse sand or gravel of the Holocene Transgression; elsewhere they are merely localized lag concentrates. Bedforms on the shore face and adjacent inner shelf tend to be nearly shore-normal with slightly acute angles opening to the northeast. Further seaward most bedforms are parallel to the coast, and to the generalized trend of the isobaths. These relationships lead to the inference that the nearshore features are the troughs of low amplitude, flow-transverse sand waves, and that they are probably responses to the intense, downwelling, along-coast flows that occur during northeaster storms. The offshore bedforms may also be responses to storm flow, but their orientation suggests that they are flow-parallel current lineations, perhaps responses to longitudinal vortices in the flow. The bedforms indicate that the shelf floor is responding to the modern hydraulic regime. Time-averaged bed load transport is directed downshelf, to the south and west. On the inner shelf there is also an offshore transport component.

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