MEPS 159:81-95 (1997)  -  doi:10.3354/meps159081

Characterisation of space-time variability in stratified and mixed coastal waters (Baie des Chaleurs, Québec, Canada): application of fractal theory

Laurent Seuront*, Yvan Lagadeuc

Université des Sciences et Technologies de Lille, URA CNRS 1363, Station Marine, BP 80, F-62930 Wimereux, France

The variability of in vivo fluorescence, temperature and salinity in the vertically stratified and well-mixed waters of the Baie des Chaleurs (Québec, Canada) was investigated as a continuous function of scale by applying the concept of fractal dimension to variogram analysis. Widely applied to the description of spatial heterogeneity, fractal dimension appears here to be a helpful descriptive tool in discriminating between homogeneity and heterogeneity in time series of both physical and biological parameters. In stratified waters, the structuration of in vivo fluorescence, temperature and salinity remains the same over time, in spite of mixing induced by the rise of a strong wind, and is shown to be associated with the global structure of the water column. In mixed waters, the situation is more complex, giving rise to specific behaviour of invivo fluorescence and salinity. In both cases, the differences observed between the fractal dimensions can be explained in terms of different ranges of scales perceived in pattern variability and thus, in the complexity of the pattern structure. We also suggest that the departure from strict selfsimilarity which seems to be associated with the vertical structure of the residual circulation is an indicator of the transitional zone between different levels of system organisation.

Space-time variability · Homogeneity · Heterogeneity · Fractal dimension · Stratified and mixed waters

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