There is large interannual and geographical variation in the distribution and abundance of phytoplankton species with in the area. However, the main pattern in the annual succession pattern is rather stabile despite variability in abiotic factors (e.g. temperature) between the years. The starting point of the spring bloom will vary between years, a variation that in large degree is controlled by the onset of necessary stability of the water column for bloom formation. Large blooms, with exception of the spring and autumn situation, might occur some years along the coast or in the open waters of the Barents Sea.
In Norwegian waters there was not observed any large aberration in the annual succession in the phytoplankton along the fixed transect (Vardø – North and Fugløya-Bear Island) in 2008. The spring bloom started in the end of April at the Bear Island transect, within the “normal” period of the spring bloom (Figure 4.3.1).
The bloom starts in the coastal waters “spreading” out into the open areas. In April the diatoms were dominating, with strain of Phaeocystis. Species within the genus Chaetoceros, especially C. socialis, and Thalassiosira nordenskioeldii was conspicuous. These species is common during the spring period. During summer the phytoplankton shows a patch distribution, with higher abundance at some station than other, also the species or groups has a more patch distribution. The phytoplankton was compound of small flagellates, dinoflagellates (naked forms, Gymnodinium and Gyrodinium), and at some stations diatoms (e.g. Leptocylindrus). As in 2007, there was observed a bloom of Emiliania huxleyi along the Norwegian coast during July to mid August. It seem like this species has become more common in this area the latest years. During autumn larger dinoflagellates, especially Ceratium spp, Dinophysis spp, and Gymnodinium spp was common along the both transects. However, at some stations, diatoms, such as Chaetoceros spp and Proboscia alata, had moderate to high abundance. All of these species is commonly found during the autumn period in the Barents Sea. In September 2008 the diatom Corethron hystrix was observed at the mid section of the transect Bear Island-Fugløya. This species has been observed occasionally in the Barents Sea before, but is regarded as more common in the Norwegian Sea, however, this year the species was in percentages the dominating species in the net samples.
Simulations of the primary production in the Barents Sea using the ROMS numerical model showed that there has been considerable interannual variation in timing of the spring bloom at the Fugløya-Bear Island section during the years 1982 to 2007 (Figure 4.3.2). Even though we suspect the model to produce the bloom somewhat too early in the year, we expect the trends to be more correct. The model results showed that the peak of the spring production (bloom) may vary with about one month from year to year and in 2007 the results indicates that the peak was the earliest for the modelled period. Also it seems to be a long term trend towards earlier spring blooming. Figure 4.3.3 shows the timing of the bloom throughout the Barents Sea in 2007. It shows that the bloom was earliest at the western part of the polar front and in the southeastern part of the Barents Sea. Also close to some of the bank areas the bloom started early. Some of these banks are very shallow and water masses may be trapped there. The bank may therefore act as a barrier to downward transport of plankton cells in the same way as a stratification of the water masses. This may explain the early bloom in the bank areas. Simulations by the SINMOD numerical model support high inter-annual variability in primary production related to inflow of Atlantic water and ice-distribution, but no long-term trend was observed in total annual primary production for the years 1995-2007. There seems to be a change in timing occurring before any eventual increases in total annual primary production is seen.
Figure 4.3.2 - 4.3.3 - Click to enlarge
