An intermittent, intermediate nepheloid layer in Emerald Basin, Scotian Shelf

Intermittent, intermediate nepheloid layers were observed on the Scotian Shelf in late April, 1987. These 10–30 m thick nepheloid layers were found between 140 and 200 m in the main part of Emerald Basin and 120–140 m in the northern basin, well below the surface mixed layer and about 90 m above the sea bed in both cases. Both biological and physical considerations are used to assess mechanisms for the observed intermediate nepheloid layers. Depths of intermediate nepheloid layers coincide with the critical depth for possible generation and amplification of internal waves with semi-diurnal (M2) internal tidal frequency. Intermittent particle resuspension at the “critical” depth on the Basin slope appears to be the likely cause of the observed intermittency of the intermediate nepheloid layers. Observations of intermediate nepheloid layers at the three stations in the main part of Emerald Basin and the northern basin indicate that this process is not a rare event, but rather a basin-wide phenomenon.