Effects of high latitude UV radiation on phytoplankton and nekton modelledfrom field measurements by simple algorithms

Irradiance measurements from the Parents Sea and coastal areas of northern Norway were used to calibrate a simple-algorithm empirical model that simul ate PAR, UVR and UVR inhibition of phytoplankton carbon assimilation. Field measurements showed that UVR levels, in addition to solar zenith angle, we re controlled by variations in cloudiness and probably also ozone layer thi ckness, The relative amount of UV-B and UV-A to PAR increased during period s with heavy cloud cover. Inhibition of phytoplankton photosynthesis, obtai ned from incubation experiments, was between 50 and 75% close to the surfac e and was detectable down to ca, 10 m depth. The common spring bloom phytop lankter Phaeocystis pouchetii was less sensitive to UVR than centric diatom s. Critical depths (D-cr) for increase in phytoplankton biomass modelled fr om a 40-year time series of meteorological data from Lofoten were shallower during periods with elevated UVR levels, but we suggest that total annual production is not severely affected, Nauplii of the copepod Calanus finmarc hicus start to feed during the post-spring bloom period, and a delayed or p rolonged spring bloom will therefore probably not affect zooplankton or cod (Gadus morhua) larvae stocks negatively. Correlation analyses between cod year class strength and modelled UVR levels (r = -0.62) in May indicate a l ink between years with high UV radiation (clear sky) and poor cod year clas ses.