Environmental effects on phytoplankton production in a Northeast Atlantic fjord, Faroe Islands

Primary production in the fjords of the Faroe Islands is usually high. Results of productivity measurements in a typical Faroese fjord (Kaldbaksfjord) in 2006 and 2007 reveal values of about 335 g C m−2 year−1, which is two to three times higher than reported from neighboring regions, such as Icelandic, west Norwegian and west Scottish fjords. The causal mechanism is high flushing rate of the euphotic zone and high influx of nutrients, relative to the surface area. On average, the majority of the production is based on new production. The productive season is from late March to early April until October. It is controlled by irradiance and occurs when the critical depth extends below the halocline. The system is highly dynamic and the plankton productivity is largely influenced by short-term fluctuations in horizontal flow and vertical mixing, influencing vertical as well as temporal variability in P/B ratio and f-ratio. Fast repetition rate fluorescence profiles revealed that Fv/Fm decreases below 0.5 when the light intensity is above 200 µE m−2 s−1 or when the nitrate + ammonium concentrations were below a threshold between 0.8 and 2 µM.