23
know very little about the metabolic activities of Antarctic phytoplankton, and wnether or not they are well adapted to their environment
is still a matter of controversy (Holm-Hansen et al., 1977; Olson, 1980;
El-Sayed and Taguchi, 1981).
Further, we still have a poor understanding of the factors which govern phytoplankton production in the Southern
Ocean.
Investigators are confounded by the fact that the ocean south
of the Polar Front contains a circumpolar phytoplankton population
living in a fairly uniform environment with sufficient light for photosynthesis (at least during spring and summer), a population that is
more or less adapted to cold temperature and has abundant nutrient salts-yet that population is not only patchy but very low in density, approaching that of oliogtrophic regions.
The nutrient levels should be able
to support a phytoplankton biomass of at least 25 ~g chl ~/l (HolmHansen and Huntley,in press).
However, the Antarctic phytoplankton
population seldom attains this density, except for the occasional
blooms referred to above.
III.
FACTORS GOVERNING PRIMARY PRODUCTION IN THE SOUTHERN OCEAN
El-Sayed and Mandelli (1965) discussed five factors which they
considered likely to control production in the Antarctic waters. They
listed: (1) light, (2) temperature, (3) inorganic nutrient salts, (4)
turbulence and (5) grazing.
In this section an attempt will be made
to update the information given in El-Sayed and Mandelli (ibid.) in
light of the data/information that has accumulated in recent years.
A. Light
Variations in incoming solar radiation between summer and
winter in the Antarctic are extreme.
The effects these variations
have on marine plant life in the circum-Antarctic waters were discussed
by El-Sayed (1971) and are illustrated in Figure 2.
Furthermore,
light penetration in Antarctic waters is determined not only by the
intensity and angle of incidence of light, surface reflectance, and
the absorption of suspended particles, but also by the presence of
thick fast ice and pack-ice which appreciably reduces the amount of
submarine illumination.
Jacques (1983) called attention to the fact
that the effect of fluctuation in the light actually received by Antarctic phytoplankton has been totally overlooked. He listed the
effects of gales (time scale in hours), of passing clouds (time scale
in minutes) and high frequency waves (time scale in seconds) as factors
which influence the vertical movement and dispersal of phytoplankton
know very little about the metabolic activities of Antarctic phytoplankton, and wnether or not they are well adapted to their environment
is still a matter of controversy (Holm-Hansen et al., 1977; Olson, 1980;
El-Sayed and Taguchi, 1981).
Further, we still have a poor understanding of the factors which govern phytoplankton production in the Southern
Ocean.
Investigators are confounded by the fact that the ocean south
of the Polar Front contains a circumpolar phytoplankton population
living in a fairly uniform environment with sufficient light for photosynthesis (at least during spring and summer), a population that is
more or less adapted to cold temperature and has abundant nutrient salts-yet that population is not only patchy but very low in density, approaching that of oliogtrophic regions.
The nutrient levels should be able
to support a phytoplankton biomass of at least 25 ~g chl ~/l (HolmHansen and Huntley,in press).
However, the Antarctic phytoplankton
population seldom attains this density, except for the occasional
blooms referred to above.
III.
FACTORS GOVERNING PRIMARY PRODUCTION IN THE SOUTHERN OCEAN
El-Sayed and Mandelli (1965) discussed five factors which they
considered likely to control production in the Antarctic waters. They
listed: (1) light, (2) temperature, (3) inorganic nutrient salts, (4)
turbulence and (5) grazing.
In this section an attempt will be made
to update the information given in El-Sayed and Mandelli (ibid.) in
light of the data/information that has accumulated in recent years.
A. Light
Variations in incoming solar radiation between summer and
winter in the Antarctic are extreme.
The effects these variations
have on marine plant life in the circum-Antarctic waters were discussed
by El-Sayed (1971) and are illustrated in Figure 2.
Furthermore,
light penetration in Antarctic waters is determined not only by the
intensity and angle of incidence of light, surface reflectance, and
the absorption of suspended particles, but also by the presence of
thick fast ice and pack-ice which appreciably reduces the amount of
submarine illumination.
Jacques (1983) called attention to the fact
that the effect of fluctuation in the light actually received by Antarctic phytoplankton has been totally overlooked. He listed the
effects of gales (time scale in hours), of passing clouds (time scale
in minutes) and high frequency waves (time scale in seconds) as factors
which influence the vertical movement and dispersal of phytoplankton