Phytoplankton Distribution in the Norwegian Sea in June, 1952 and 1953
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1. The quantitative observations which have been made up to now (cp. Fig. 1) have demonstrated that the Norwegian Sea is an area where great variations are encountered in the phytoplankton vegetation. 2. Within the cold water masses on the western side of Bear Island and Spitsbergen the vegetation during the spring maximum is characterized by Boreal- and Arctic-neritic diatoms and Phaeocystis. poucheti. A pronounced discontinuity layer within the upper strata during spring and summer presumably restricts the supply of nutrients from lower levels. It may, therefore, be expected that a poor phytoplankton society prevails after the spring maximum in June. The observations seem to indicate that a society with the small diatom Fragilaria nana as the predominant species succeeds the abundant neritic vegetation in the layers bordering Atlantic water. 3. The predominant species in the cold water masses off Spitsbergen are different from those recorded from the East Greenland Polar current in the Denmark Strait during the corresponding period of the annual cycle. 4. In the Polar - Arctic water masses north to north-east of Jan Mayen the spring increase seems to have a fairly early onset, and is over in June, although the surface layers are still homogeneous to a point below the compensation depth. The observations indicate that, in spite of the lack of any pronounced density gradients, turbulent activity may be small. The investigations in June 1953 showed that when bottom water is formed in this area, the onset of the population's spring increase is delayed. As soon as the sinking of the heavy, cooled surface water is terminated, the population increases. The vegetation was composed of oceanic as well as of neritic species. 5. In the Atlantic water masses observations are as yet too scanty to allow the presentation of a general picture of the phytoplankton distribution and seasonal changes. We restrict ourselves to stressing how variable conditions may be within any given area. In June 1953 three vegetation areas could be discerned within the Atlantic water masses where observations were made and to a certain extent they could be correlated with currents. In other parts of the Atlantic water masses in the Norwegian Sea the hydrograpbic conditions may be even more variable and it is to be expected that they may induce a corresponding variation in the phytoplankton. Light, stability and grazing may be expected to control the development of the phytoplankton populations in Atlantic water during spring and summer. The available investigations have shown how the establishment of a certain degree of stabilization leads to a. quick increase in the population, which at this time has diatoms as its main component and important supplements of coccolithophorids and dinoflagellates. 6. Three different currents, apart from the Icelandic coastal curent, pass through a section to the east of Iceland. The phytoplankton observations have demonstrated that there are also three corresponding vegetation areas, which, however, show signs of lateral mixing between the water masses of the currents.
SeriesFiskeridirektoratets skrifter, Serie Havundersøkelser
vol 12 no 10