Phytoplankton from two sub-Arctic fjords in northern Norway 2002–2004: I. Seasonal variations in chlorophyllaand bloom dynamics

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Abstract
Chlorophyll a, meteorology and hydrography were sampled during a 3 year period in Altafjord and Porsangerfjord. The analysis demonstrated a decoupling between spring bloom progression and the classical ‘Sverdrup’ regulators, i.e. there was no correlation between spring bloom biomass and critical depth, mixed or station depth and irradiance. The only significant correlation was linear between bloom magnitude and day length. We also observed significant correlations between log chlorophyll a and critical depth, irradiance and heat flux. From early March to mid-May, day length increases from 7 to 24 h in the area, whereas daily integrated irradiance increases ca. 14 times. Then, if blooms have not yet triggered early in April, water turbidity will remain low and critical depth will deepen rapidly, causing blooms to start after this date, i.e. irradiance will become the main forcing function if initial stocks are present. Another characteristic feature in the area is that spring bloom concentrations are low and that production is more spread out throughout the growth season, contrary to what is common further south (spring bloom, summer recession and autumn bloom).

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