| dc.description.abstract | 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. | |
