AN INTERMITTENT, INTERMEDIATE NEPHELOID LAYER IN EMERALD BASIN, SCOTIAN SHELF

Intermittent, intermediate nepheloid layers were observed on the scoti an shelf in late April, 1987. These 10-30 m thick nepheloid layers wer e found between 140 and 200 m in the main part of Emerald Basin and 12 0-140 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 physic al considerations are used to assess mechanisms for the observed inter mediate nepheloid layers. Depths of intermediate nepheloid layers coin cide with the critical depth for possible generation and amplification of internal waves with semi-diurnal (M(2)) internal tidal frequency. Intermittent particle resuspension at the ''critical'' depth on the Ba sin slope appears to be the likely cause of the observed intermittency of the intermediate nepheloid layers. Observations of intermediate ne pheloid 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.