SPATIO-TEMPORAL VARIABILITY OF PHYTOPLANKTON PIGMENTS IN THE 
GULF OF ST. LAWRENCE AS MEASURED BY CZCS 
Pierre Larouchel, César Fuentes-Yaco? and Alain F. Vézinal 
1 Institut Maurice-Lamontagne, Fisheries and Oceans Canada, 
P.O. Box 1000, Mont-Joli, Québec, Canada G5H 3Z4 
2 Centre Océanographique de Rimouski, Université du Québec à Rimouski, 310 allée des Ursulines 
Rimouski, Québec, Canada G5L 3A1 
Commission VII, Working Group VIII 
KEY WORDS: Sea,Measurement,Multitemporal,Spatial,Environment,CZCS,Phytoplankton,Ocean Colour 
ABSTRACT 
This study examined surface phytoplankton pigments distribution (chlorophyll a plus phaeophytin) 
in the Gulf of St. Lawrence (GSL), Canada using eighty Coastal Zone Color Scanner (CZCS) images 
taken between April and September from 1979 to 1981. The results generally agree with historical 
knowledge of phytoplankton pigment distribution in the gulf obtained using traditional shipboard 
methods. However, the CZCS imagery allowed better identification of both temporal (seasonal ang 
interannual) and spatial (mesoscale) pigment patterns. The results suggest that the seasonal 
cycle appears to be dominated by increases in pigment concentration in late summer-early fall, 
Finaly, the results also indicate that interannual variations in pigment concentration may 
exceed those observed on an seasonal scale. 
RESUME 
Cette étude examine la distribution des pigments phytoplanctoniques (chlorophylle a plu 
pheophytine) dans le Golfe du saint-Laurent à l'aide de quatre-vingt images du capteur Coastal 
Zone Color Scanner (CZCS) captées entre le mois d'avril et septembre des années 1979 à 1981. Les 
résultats concordent généralement avec la connaissance de la distribution du phytoplancton 
obtenue à l'aide des techniques d'échantillonnage traditionnelles. Les images CZCS ont toutefois 
permis de mieux identifier les patrons de distribution temporels (saisonniers et interannuels) 
et spatiaux (méso-échalle). Les résultats suggèrent que le cycle saisonnier est dominé par une 
augmentation de la concentration des pigments chlorophylliens à l'automne. Finallement, les 
résultats indiquent aussi que la variation inter-annuelle de la concentration des pigments 
puisse excéder la variabilité saisonnière. 
1. INTRODUCTION previous results obtained using CZCS data and 
the future availability of new ocean color 
Due to its large scale and because the sensors (SeaWiFS, OCTS, MODIS), a research 
seasonal phytoplankton cycle is influenced by program was builded to evaluate primary 
the local oceanographic (circulation, stra- production in the GSL using remote sensing 
tification, runoff, ice) and meteorological techniques. As a first step of this program 
(wind, radiation, temperature) characteristics it was decided to analyze the historical CZCS 
as well as by the availability of nutrients, data set in order to gain some insight of the 
the Gulf of St. Lawrence (GSL) located in large scale physical-biological interactions 
eastern Canada cannot be considered a occuring in the GSL ecosystem. 
homogeneous ecosystem. Knowledge of 
phytoplankton pigments and primary production Several particularities make the GSL a complex 
gathered over the years during oceanographic optical medium for the retrieval of phyto- 
cruises shows broad patterns of spatio- plankton pigments using remote sensing. First 
temporal variability to exists in the GSL. The regional and local atmospheric conditions 
recent problems encountered with eastern cause dynamic interactions between marine and 
Canadian fish stocks emphasized the need for terrestrial aerosols. Second, the basil 
long-term time series of primary production in receives the enormous output from the St. 
the GSL. Due to the existing spatio-temporal Lawrence river, including organic and 
variability of its driving physical forces, it inorganic matter which affects the remote 
is however almost impossible to devise a sensing of phytoplankton pigments (Case II 
monitoring system of primary production over waters). Finally, diverse phytoplankton 
the entire GSL using traditional oceanographic communities also contribute differently to the 
methods of sampling. Other approaches were water leaving radiances. In particular, the 
thus sought to better evaluate this important GSL is known for its: sporadic occurences 0 
parameter of the ecosystem. In the light of coccolithophores blooms. 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996 
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