the two data sets were highly correlated with 
a r^ of 0.89. Moreover, the spatial pattern of 
in situ values in the northeastern gulf bet- 
ween 20 and 28 May 1981 corresponds closely 
with two images taken during that time frame 
bringing further confidence in the selected 
atmospheric correction process. 
signal 
Variability of underwater 
contamination 
The IHS analysis showed that the areas conta- 
minated principally by suspended matter in the 
lower St. Lawrence estuary (LSLE) and western 
GSL or by coccoliths in the eastern GSL were 
relatively small and well defined in time and 
space. They also appeared to covary positively 
with the temporal pigment averages. The 
pigment concentrations estimated by the 
selected approach should thus be reasonably 
accurate for most of the times and areas 
covered by the database. 
3. RESULTS AND DISCUSSION 
In this paper, a powerful and useful remote 
sensing tool was used to measure phytoplankton 
pigment concentrations in the GSL and build 
the first complete data set of satellite 
images showing the pigment distribution in the 
GSL (Fuentes-Yaco et al., 1995). This data set 
will be now analyzed to evaluate both the 
spatial and temporal variability of phyto- 
plankton pigments in the GSL. 
Spatial patterns 
The major spatial feature seen in the seasonal 
(Fig. 2) and annual (Fig. 3) composites is the 
persistent west to east gradient between the 
LSLE,” the northwest gulf and the central- 
eastern gulf regions. This global distribution 
of pigments in the GSL is closely linked to 
major dynamical features known to exist. The 
LSLE, Gaspé Current, and northwestern qulf 
exhibited the highest concentrations of 
chlorophyll-like pigments throughout the year 
due to the presence of gyres and wind-induceq 
upwellings. In this regard, these areas may be 
considered as pigment pumps, helping to 
increase concentration in the central and 
southern regions (Magdalen  Shallows) by 
advection through the Honguedo Strait. In 
shallower areas such as Baie des Chaleurs and 
the Magdalen Islands, other factors, including 
wind stress, contribute to the increase in 
pigment concentrations through vertical mixing 
and local ,nutrient enrichment. Downwelling 
processes in the northeastern GSL appear to be 
responsible for the low surface pigment 
concentrations usually found throughout the 
year in this region. However, some limited 
production was detected in northern Esquiman 
Channel, which may be linked to wind-driven 
upwelling. 
Seasonal variability 
The calculated seasonal pigment composites 
(Fig.2) showed high pigment concentrations in 
spring and low ones in summer (Table 1). 
However, the results also indicated that the 
highest pigment concentrations occurred during 
fall, which has not been reported previously. 
The observed seasonal cycle of chlorophyll- 
like pigments is characterized mostly by 
changes in the areal extent of high pigment 
values rather than in a general large-scale 
rise and fall in concentrations. These areas 
extend far ’éastward during August ‘end 
September and cover even larger areas than 
during spring. 
Table 1. Statistics (mean and standard error) of phytoplankton pigment concentration (mg md) 
by season and year. 
Annual means 
Region Statistic Spring Summer 
LSLE mean 1e. 3 1.4 
SE 0.2 0.2 
GSL mean 0.6 0.6 
SE 0:4 0.1 
Interannual variability 
Yearly means showed that 1980 had the highest 
phytoplankton pigment concentrations of the 
three years studied (Table 1), with the area 
of strong pigment concentration in the western 
GSL extending from the LSLE to Northumberland 
Strait (Figure 3). During that year, high 
pigment values were also observed along the 
northern shore of the GSL and around the 
Magdalen Islands. The year 1979 was 
408 
Seasonal means 
Fall 1979 1980 1981 Average 
tend lcd 1.6 1.2 1.4 
0-2 0.3 0.2 0:2 0.1 
0.8 0.6 0.8 0.5 0.6 
Qoi 0.1 0.1 0.1 0.1 
characterized by intermediate mean values, 
with the areal pigment distribution being 
close to the three-year average. Finally, 198 
seemed to have the lowest concentrations of 
the three years. However, the northwestern 
Esquiman Channel showed elevated and 
persistent pigment concentrations in 1981. 
The observed temporal variations of the 
spatial chlorophyll patterns parallel to some 
extent the differences in salinity % 
influenced by estuary runoff (Bugden et al 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996