Data collected in the estuary and Gulf of St. Lawrence in summer 1989 and 1990 were analyzed to quantify horizontal variations in the spectral values of the specific absorption coefficient of phytoplankton in different natural environments and to examine the conscquenccs of assuming this specific absorption spectrum as constant when estimating primary production.Absorption spectra of total particles were measured with the glass-fiber filter technique, and absorption by phytoplankton was estimated numerically. We analyzed 369 spectra to estimate the actual extent of variations in the specific absorption coefficient by phytoplankton at several spatial scales in the St. Lawrcncc system. The potential impact of these variations on the estimation of primary production was assessed for various ecosystems with a spectral primary production model. This model takes into account chlorophyll variations with depth together with associated variations in attenuance and variations in partitioning of the various absorbing components in going from eutrophic to oligotrophic waters. Using this model, we found that, at large scale (> 1,000 km), the relative error in estimating primary production can bc as high as 24% in oligotrophic waters when a constant specific absorption spectrum is assumed. Field measurements of primary production support results dcrivcd from the model

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The discharge of the St. Lawrence River drives a buoyant jet which extends along the south shore of the lower St. Lawrence estuary and, combining with the northwest Gulf of St. Lawrence cyclonic gyre, becomes the Gaspé Current. In both the estuarine jet and the Gaspé Current, strong lateral and vertical shears are present. Satellite thermal imagery has shown that the Gaspé Current is unstable. Its instabilities are manifested as prominent wave disturbances and eddy features. We use satellite thermal images from 3 different years to show that unstable disturbances are also characteristic of the estuarine jet. We update previous work to show that Gaspé Current is both baroclinically and barotropically unstable. Our model studies also show that this conclusion is valid for the estuarine jet as well. Finally, we discuss a sequence of satellite images showing the development of an unstable disturbance apparently triggered by an eastward wind pulse.