Short-Term Covariability of Chlorophyll and Temperature in the St. Lawrence Estuary

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Abstract
Time series of chlorophyll a fluorescence and temperature taken at a depth of 1 m were recorded at 4-min intervals for 136.5 h, at an anchor station located in the Middle Estuary of the St. Lawrence. The sampling program was carried out during the transition from neap tides to spring tides. Power spectral analysis was applied to the series and variance spectra were estimated. Coherency spectra between fluorescence and temperature were also computed. Results indicate that chlorophyll distribution was controlled by physical processes during neap tides. Conversely, lesser amounts of chlorophyll a per cell and lesser primary production rates were noted during spring tides. A flattening of the chlorophyll spectrum was observed for this part of the study. This result was interpreted in terms of the poor physiological state of the phytoplankton population that was sampled during the second part of the study, a different density structure being present due to the change in tidal energy. Key words: time series, chlorophyll, temperature, spectral analysis, St. Lawrence Estuary

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