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We investigated the ultraviolet radiation (UVR) transmission properties of Norwegian oceanic, coastal and fjord waters, and how they influence the primary production and vertical distribution of phytoplankton. Values of the 1% UVR attenuation depth and diffuse attenuation coefficients (K d ) in the Greenland and Norwegian Seas (GNS), in the coastal waters of south-western Norway (SWN) and in the Samnanger fjord (SAF) are presented. Maximum penetration of UVR in the GNS was confirmed by K d (320) = 0.25 m -1 , and mimimum penetration in the SAF, by K d (320) = 9 m -1 . In the GNS, K d and chlorophyll a (chl a) were closely correlated, while coloured dissolved organic matter (CDOM) was the main contributor to ultraviolet (UV) attenuation in the SAF. Also, in SWN waters, CDOM was more important than chl a for UV attenuation, but less important than in SAF waters. In GNS and SAF waters the average vertical distribution of chl a had its maximum in the upper 10 and 7.5 m of the water column, respectively, while in SWN waters it had its maximum at 20 m. The depths with the highest photosynthetic rates per unit volume decreased successively from the oceanic waters of the GNS via the coastal waters of the SWN to the fjord waters of the SAF. Under similar PAR intensities, however, the water column photosynthetic efficiency (integrated carbon assimilation/chl a ratio) was highest in SWN waters. Maximum and mean percentage potential for inhibition of the estimated (from PAR and UV) primary production due to UVR at a depth of 5 m were 11 and 4.3% in the GNS, 3.2 and 0.9% in the SWN and 0.5 and 0.1% in the SAF. The UVR potential for inhibition was significant down to a depth of 10 m in the GNS, down to a depth of 5 m in the waters of the SWN, while it was seldom found deeper than 3 m in the SAF. These variations could be ascribed to differences in CDOM concentrations and mixed-layer depths. The optical properties of the investigated water masses were found to be highly influenced by the circulation patterns. KEY WORDS: UV transmission · Norwegian waters · Phytoplankton · Primary production Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 305: 2005 total ozone has been observed at middle and high latitudes in the Northern Hemisphere during the last decades (Stolarski et al. 1992, Jokela et al. 1993, Varotsos et al. 1998, Dahlback 2002. According to Austin et al. (1992), Bjørn et al. (1998) and Hessen (2002), this tendency is expected to continue in the 21st century. In addition, there is a tendency towards more rapid depletion of the ozone layer over Scandinavia than over most other geographical regions at corresponding latitudes. In contrast to the antarctic ozone hole, which occurs regularly both on a spatial and a temporal scale (Hofmann et al. 1992, Davidson & van der Heijden 2000, the arctic ozone hole seems to occur irregularly (Stamnes et al. 1988, Jokela et al. 1993). The radiation levels within both the visible and the UV bands decrease with increasing la...

There is very little information in the literature about how phytoplankton flagellates respond to rapid changes in salinity (e.g., haloclines of different strength). Here we present such data obtained from experiments with Tetraselmis sp. (Prasinophyceae) in a specially designed artificial water column. The experiments were performed with surface salinities varying from 27.4 to 33.4‰, whereas bottom salinities were essentially constant (34.0-34.6‰). Cells were introduced near the bottom. The first stage of the ascent was an accumulation of cells in the lower part of the halocline. The second was a transit to the upper part of the halocline after a variable time lag, and the third stage was a further ascent to the surface layer, again after a variable time lag. Our results reveal a strong positive phototaxis of the swimming cells under continuous surface irradiances in the range 17-144 mol quanta m Ϫ2 s Ϫ1 . Maximum swimming speeds were found to be 0.9 m h Ϫ1 . Increasing halocline strength (⌬S ϭ 0.7, 3.0, and 6.6‰), resulted in reduced swimming activity, but the cells managed to pass through after an adaptation period. Under a 14 : 10 light : dark (LD) cycle, the cell concentrations of the bottom layer decreased gradually for each cycle, and cells accumulated in the surface layer during the light period. During the dark period, cell concentrations were also increasing in the halocline for each cycle. A downward migration started about 2 h before the light period ended and was slower than the ascent of cells from the halocline. It therefore seems that positive phototaxis was stronger than the positive geotaxis as a driving force of cell motility. We conclude that strong haloclines can prevent phytoplankton flagellates in the surface layer from reaching the nutrient-rich deeper layer during the night and therefore play an important regulating role in the bloom dynamics of phytoplankton.

Oceans cover about 70% of the surface of the Earth and represent an important source of food. To obtain information about primary production, propagation of phytoplankton blooms, nutrient status, and temperature, the marine environment is continuously monitored both in situ and from satellites. In this context, in situ optical measurements are indispensable because they are fast and suited for automated routine operation. Among the most commonly measured parameters in situ are the absorption and attenuation coefficients, the diffuse attenuation coefficient for downwelling irradiance, and natural fluorescence. From satellite measurements, one can estimate the water-leaving radiance, and in the laboratory, the chlorophyll concentrations of water samples can be measured by fluorometric or spectrophotometric methods.The volume-scattering function (VSF) is an important optical property that is not routinely measured. Thus, the measurements of Petzold (1977), which date back to the 1970s, are still commonly used to represent the VSF for seawater. Among the laboratory measurements of the VSF relevant for our study, the data obtained by Privoznik et al. (1978) and Morel and Bricaud (1986) AbstractWe present an improved technique for measurements of the volume-scattering function (VSF) for marine particles, which include added spectral information, a novel optical design of the sample container, and two new ways of eliminating unwanted reflections. The novel optical design enables us to measure an angular range comparable to the largest angular range previously reported. Our improved setup eliminates the need for an empirically based data correction and reveals interesting characteristics of the VSF for different phytoplankton species. Measurements with our improved setup provide information that is important to understand and simulate radiative transfer in the ocean.

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