136
J . E . (f. RAYMONT
and phosphate and primary production is provided by the major upwelling areas such as those off West Africa, off Chile and Peru, and off
the coast of California. In each region the relatively high concentrations
of nitrate and phosphate are accompanied by rich growths of phytoplankton (cf. Hart, 1953; Hart and Currie, 1960; Clowes, 1950, 1954;
Gunther, 1936; Sverdrup and Allen, 1939). Just recently the investigations of the Indian Ocean Expedition have pointed to a fairly rich production off southern Arabia associated with upwelling water. Above all,
in the Antarctic (Hart, 1934, 1942), constant upwelling on a relatively
gigantic scale permits a high rate of production as long as the light conditions are sufficient for photosynthesis. Areas of divergence may also
be marked by nutrient-rich water reaching the surface. The well-known
divergence close to the Equator in the Pacific Ocean is marked by a
high rate of productivity (Austin and Brock, 1959; Hela and Laevastu,
1962) in the rich surface water. Holmes (1958) and Bogorov (1958)
similarly relate high rates of production and of standing crop in Pacific
waters to areas marked by nutrient-richer surface water. Indeed, turbulence, convection currents, current boundaries, as well as more major
upwelling, are of significance in renewing phosphate and nitrate to the
surface and raising primary production.
In the absence of such vertical water movements, generally in
tropical and subtropical regions a strong thermocline is permanently
established, and the lack of nitrate and phosphate occurring in the
euphotic zone puts a sharp brake on primary production. Admittedly
much of the earlier work dealt with the standing crop of phytoplankton
in tropical and subtropical areas rather than with primary production,
but the work especially of Steemann Nielsen (1954) and Steemann
Nielsen and Aabye Jensen (1957) permits some summary to be made
for production. Thus for tropical areas the rate of primary production
is low amounting to some 0.1 to 0 . 2 g C/m2/day, and in areas such as the
Sargasso Sea, where the upper water layers are especially depleted in
nutrients, the production may be even lower. As against this, inshore
temperate areas which are fairly rich in nutrients and also rich upwelling areas anywhere in the world may show a production varying
from 0.5 to 3.0 gC/m2/day.
If we assume a direct dependence of production on nutrient level, it
must be admitted that in temperate regions the fall in phytoplankton
after the spring increase does not always precisely accompany the
reduction in nutrient concentration. The picture is confused here by
our inability often to distinguish between the standing crop of plankton
and rates of production. During the summer also the standing crop
may be maintained at a relatively low level by grazing although production may be proceeding at a somewhat higher rate than was originally
J . E . (f. RAYMONT
and phosphate and primary production is provided by the major upwelling areas such as those off West Africa, off Chile and Peru, and off
the coast of California. In each region the relatively high concentrations
of nitrate and phosphate are accompanied by rich growths of phytoplankton (cf. Hart, 1953; Hart and Currie, 1960; Clowes, 1950, 1954;
Gunther, 1936; Sverdrup and Allen, 1939). Just recently the investigations of the Indian Ocean Expedition have pointed to a fairly rich production off southern Arabia associated with upwelling water. Above all,
in the Antarctic (Hart, 1934, 1942), constant upwelling on a relatively
gigantic scale permits a high rate of production as long as the light conditions are sufficient for photosynthesis. Areas of divergence may also
be marked by nutrient-rich water reaching the surface. The well-known
divergence close to the Equator in the Pacific Ocean is marked by a
high rate of productivity (Austin and Brock, 1959; Hela and Laevastu,
1962) in the rich surface water. Holmes (1958) and Bogorov (1958)
similarly relate high rates of production and of standing crop in Pacific
waters to areas marked by nutrient-richer surface water. Indeed, turbulence, convection currents, current boundaries, as well as more major
upwelling, are of significance in renewing phosphate and nitrate to the
surface and raising primary production.
In the absence of such vertical water movements, generally in
tropical and subtropical regions a strong thermocline is permanently
established, and the lack of nitrate and phosphate occurring in the
euphotic zone puts a sharp brake on primary production. Admittedly
much of the earlier work dealt with the standing crop of phytoplankton
in tropical and subtropical areas rather than with primary production,
but the work especially of Steemann Nielsen (1954) and Steemann
Nielsen and Aabye Jensen (1957) permits some summary to be made
for production. Thus for tropical areas the rate of primary production
is low amounting to some 0.1 to 0 . 2 g C/m2/day, and in areas such as the
Sargasso Sea, where the upper water layers are especially depleted in
nutrients, the production may be even lower. As against this, inshore
temperate areas which are fairly rich in nutrients and also rich upwelling areas anywhere in the world may show a production varying
from 0.5 to 3.0 gC/m2/day.
If we assume a direct dependence of production on nutrient level, it
must be admitted that in temperate regions the fall in phytoplankton
after the spring increase does not always precisely accompany the
reduction in nutrient concentration. The picture is confused here by
our inability often to distinguish between the standing crop of plankton
and rates of production. During the summer also the standing crop
may be maintained at a relatively low level by grazing although production may be proceeding at a somewhat higher rate than was originally