264
D. H. CUSHINO
coast. It shows the movement towards the pole of thc coastal upwelling
systems from spring to autumn as the subtropical high intensifies, and
the strengthening of divergence along the Equatorial Current in winter
and spring. The diagram does not show that events in the southern
hemisphere are bigger and more persistent, which they are. This may
be because stronger winds originate in the Southern Ocean, or because
the coastlines have the best shape for the seasonal distribution of the
direction of the trade winds. The distribution of divergences and convergences is taken from Hidaka and Ogawa’s (1958) charts.
There are wind-driven upwellings and geostrophic upwellings, both
in coaatal areas and in oceanic areas. Coastal upwelling is generated by
winds blowing parallel to the shore towards the equator, as in the major
upwellings, or is generated geostrophically by the tilt of a current, as in
the Somali Current (Stommel and Wooster, 1965). Some areas may include both wind-generated upwellings and geostrophic upwellings, as
for example, off the Malabar coast (Darbyshire, 1967). There is a.
specialized form of upwelling off Cabo Frio in Brazil where warm salty
water offshore sinks and is replaced inshore by cooler less salty water
and this process is assisted by north-east winds (Emilsson, 1961).
Oceanic upwelling includes both the divergences due to the vorticity of
the wind stress, all around the subtropical anticyclones, and the
geostrophic upwellings within the equatorial system itself, as for example above the undercurrent and in the domes.
111. THE BIOLOGICAL BACKGROUND
A. The production cycle in an upwelling area
In temperate waters, the pattern of production cycles is dominated
by seasonal changes. During the winter, production cannot take place
when the depth of mixing is greater than the critical depth, at which
production equals respiration, both integrated from the surface
(Sverdrup, 1953). Production starts when the critical depth becomes
greater than the depth of mixing. The depth at which the rate of
production equals the rate of respiration is called the compensation
depth. After production starts, its rate of development is governed by
the ratio of compensation depth to depth of mixing (Cushing, 1962).
So the rate at which production develops in the temperate spring is
determined by the amount of sunlight and the strength of the winds, and
other factors causing mixing, all of which vary seasonally.
The production cycle in an upwelling area resembles that in temperate waters. The cool water which originates from depths of less than
D. H. CUSHINO
coast. It shows the movement towards the pole of thc coastal upwelling
systems from spring to autumn as the subtropical high intensifies, and
the strengthening of divergence along the Equatorial Current in winter
and spring. The diagram does not show that events in the southern
hemisphere are bigger and more persistent, which they are. This may
be because stronger winds originate in the Southern Ocean, or because
the coastlines have the best shape for the seasonal distribution of the
direction of the trade winds. The distribution of divergences and convergences is taken from Hidaka and Ogawa’s (1958) charts.
There are wind-driven upwellings and geostrophic upwellings, both
in coaatal areas and in oceanic areas. Coastal upwelling is generated by
winds blowing parallel to the shore towards the equator, as in the major
upwellings, or is generated geostrophically by the tilt of a current, as in
the Somali Current (Stommel and Wooster, 1965). Some areas may include both wind-generated upwellings and geostrophic upwellings, as
for example, off the Malabar coast (Darbyshire, 1967). There is a.
specialized form of upwelling off Cabo Frio in Brazil where warm salty
water offshore sinks and is replaced inshore by cooler less salty water
and this process is assisted by north-east winds (Emilsson, 1961).
Oceanic upwelling includes both the divergences due to the vorticity of
the wind stress, all around the subtropical anticyclones, and the
geostrophic upwellings within the equatorial system itself, as for example above the undercurrent and in the domes.
111. THE BIOLOGICAL BACKGROUND
A. The production cycle in an upwelling area
In temperate waters, the pattern of production cycles is dominated
by seasonal changes. During the winter, production cannot take place
when the depth of mixing is greater than the critical depth, at which
production equals respiration, both integrated from the surface
(Sverdrup, 1953). Production starts when the critical depth becomes
greater than the depth of mixing. The depth at which the rate of
production equals the rate of respiration is called the compensation
depth. After production starts, its rate of development is governed by
the ratio of compensation depth to depth of mixing (Cushing, 1962).
So the rate at which production develops in the temperate spring is
determined by the amount of sunlight and the strength of the winds, and
other factors causing mixing, all of which vary seasonally.
The production cycle in an upwelling area resembles that in temperate waters. The cool water which originates from depths of less than