General Features of Dinoflagellage Material Collected by the "Anton Bruun"
169
can be surmised that the area is much less productive during other seasons when upwelling
is not present.
Over the main areas of the central and western Indian Ocean dinoflagellates were
more uniformly abundant during the SW monsoon period. During the NE monsoon the
distributions were more discontinuous with large quantities present only at a few stations,
these being apparently situated in the shear zones between the Equatorial Currents and
Countercurrent. The area immediately to the north of the Seychelles Platform was
particularly rich in dinoflagellates. BAILEY (1968) has reported that zooplankton is also
abundant in this locality during March.
In view of the few observations of north-south shifts in surface features of the
southern parts of the Indian Ocean, this requires more detailed evaluation. There is a
tendency to ignore this possibility and to combine the results of sampling in the southern
parts, assuming that seasonal effects are minimal here. TAYLOR (MS, 1964; 1967) found
considerable seasonal differences in the distribution of the phytoplankton in the SW
Indian Ocean, apparently correlated chiefly with the formation and breakdown of a
strong summer thermocline and variations in the strength of the Agulhas Current.
Finally, mention may be made of the detrital material observed during the analyses
for it appears that detritus may constitute a considerable fraction of the particulate
carbon in some cases of high productivity in the Indian Ocean, particularly the Arabian
Sea (MULLIN, 1965). The stations at which high detrital content was apparent under
microscopic observations were also, in general, stations where either diatoms, dinoflagellates of both, were abundant. They were stations 154, 284 - 285, 291, 294, 297,
300,306 (very great), 318 and 374.
169
can be surmised that the area is much less productive during other seasons when upwelling
is not present.
Over the main areas of the central and western Indian Ocean dinoflagellates were
more uniformly abundant during the SW monsoon period. During the NE monsoon the
distributions were more discontinuous with large quantities present only at a few stations,
these being apparently situated in the shear zones between the Equatorial Currents and
Countercurrent. The area immediately to the north of the Seychelles Platform was
particularly rich in dinoflagellates. BAILEY (1968) has reported that zooplankton is also
abundant in this locality during March.
In view of the few observations of north-south shifts in surface features of the
southern parts of the Indian Ocean, this requires more detailed evaluation. There is a
tendency to ignore this possibility and to combine the results of sampling in the southern
parts, assuming that seasonal effects are minimal here. TAYLOR (MS, 1964; 1967) found
considerable seasonal differences in the distribution of the phytoplankton in the SW
Indian Ocean, apparently correlated chiefly with the formation and breakdown of a
strong summer thermocline and variations in the strength of the Agulhas Current.
Finally, mention may be made of the detrital material observed during the analyses
for it appears that detritus may constitute a considerable fraction of the particulate
carbon in some cases of high productivity in the Indian Ocean, particularly the Arabian
Sea (MULLIN, 1965). The stations at which high detrital content was apparent under
microscopic observations were also, in general, stations where either diatoms, dinoflagellates of both, were abundant. They were stations 154, 284 - 285, 291, 294, 297,
300,306 (very great), 318 and 374.