Since 1997, the Remote Sensing Laboratory of the Maurice-Lamontagne Institute (Dept. of Fisheries and Oceans, Canada) has been conducting a research program to validate ocean color images for the mixed type Ⅰ and Ⅱ waters of the St. Lawrence estuary and Gulf. This paper presents the results from the second seagoing expedition which took place in the fall of 1998. Results show that in the fall period, chlorophyll and suspended sediment concentrations were low throughout the system with almost no vertical variation inside the surface mixed layer. The phytoplankton community was dominated by microflagellates and the algal biomass was the major contributor to the particulate carbon and nitrogen pool. The influence of freshwater associated properties (CDOM, sediments) was restricted to a relatively small region at the head of the St. Lawrence estuary. In situ measurements showed that the optically important processes all take place in the water column upper mixed layer with CDOM and phytoplankton being the two major factors influencing water color.
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