THE PRODUCTION O F M S R I N E I'LANKTON
153
crop very greatly, although primary production is continuing at a very
high level, so that crop estimates may give misleading impressions of
production (vide infra).
There is a marked tendency at higher latitudes for the spring increase
to occur much later, for example, in May or June as recorded by Gran
(1931), Steemann Nielsen (1935), Kreps and 'Jerjbinskaya (1930), and
Gillbricht (1959), in the Arctic. Digby (1953) did not obtain any appreciable phytoplankton production until May o f eastern Greenland; the
peak density occurred in July, with a smaller scxondary peak in August,
but the whole production was finished by September. Corlett (1953)
also shows differences in timing of the spring diatom outburst with
latitude in various oceanic areas of the northern Atlantic. In the
Labrador Sea, Holmes (1956) finds the double peak in phytoplankton
production; until March there is virtually no algal growth owing to the
marked instability of the water column and the poor light conditions.
The spring peak occurs about May and June, a,nd there is a smaller rise
in September. Zenkevitch (1963) has summarized the position for the
Arctic: the nearer to the Pole, the later becomes the vernal outburst and
the more rapidly is it over. In the Circumpolar Ocean, for example, the
phytoplankton burst lasts hardly more than one month (August); in the
Laptev Sea the outburst lasts from the end of June to about the end of
September. On the other hand, in the most southern of the sub-Arctic
seas, the south-western Barents Sea, the period of phytoplankton
growth may approach 8 months (April to October/November), and there
is a typical spring and smaller autumn bloom. In. the Antarctic, Hart
(1934, 1942) has also shown that the timing of the spring increase
becomes later as one proceeds farther south. Not only does the outburst
become later, but the amount of time during which diatom growth
proceeds becomes shorter until at the highest latitudes there may be
only one short continuous burst of phytoplankton production.
Although typically in north-western Europe and the north-eastern
American coast the spring increase is about March, the phytoplankton
flowering may occur earlier; for example, Ccmover (1956) and Riley
(1952) found an increase in early February in Long Island Sound and
Block Island Sound, and Fish (1925) believes that at Woods Hole the
increase is as early as December. This earlj flowering may depend
partly on the sheltering of waters in these areas. Certainly the timing of
the increase is not entirely associated with latitude. Thus Riley (1957)
recorded for the North Sargasso Sea (latitude :35"N) a small diatom increase as late as April and this was confirmed by Hulburt et al. (1 960)
off Bermuda. However, Menzel and Ryther (1960; 1961) find slightly
farther south that a winter flowering may occur in any month between
November and April. I n contrast to temperahe latitudes, in tropical
153
crop very greatly, although primary production is continuing at a very
high level, so that crop estimates may give misleading impressions of
production (vide infra).
There is a marked tendency at higher latitudes for the spring increase
to occur much later, for example, in May or June as recorded by Gran
(1931), Steemann Nielsen (1935), Kreps and 'Jerjbinskaya (1930), and
Gillbricht (1959), in the Arctic. Digby (1953) did not obtain any appreciable phytoplankton production until May o f eastern Greenland; the
peak density occurred in July, with a smaller scxondary peak in August,
but the whole production was finished by September. Corlett (1953)
also shows differences in timing of the spring diatom outburst with
latitude in various oceanic areas of the northern Atlantic. In the
Labrador Sea, Holmes (1956) finds the double peak in phytoplankton
production; until March there is virtually no algal growth owing to the
marked instability of the water column and the poor light conditions.
The spring peak occurs about May and June, a,nd there is a smaller rise
in September. Zenkevitch (1963) has summarized the position for the
Arctic: the nearer to the Pole, the later becomes the vernal outburst and
the more rapidly is it over. In the Circumpolar Ocean, for example, the
phytoplankton burst lasts hardly more than one month (August); in the
Laptev Sea the outburst lasts from the end of June to about the end of
September. On the other hand, in the most southern of the sub-Arctic
seas, the south-western Barents Sea, the period of phytoplankton
growth may approach 8 months (April to October/November), and there
is a typical spring and smaller autumn bloom. In. the Antarctic, Hart
(1934, 1942) has also shown that the timing of the spring increase
becomes later as one proceeds farther south. Not only does the outburst
become later, but the amount of time during which diatom growth
proceeds becomes shorter until at the highest latitudes there may be
only one short continuous burst of phytoplankton production.
Although typically in north-western Europe and the north-eastern
American coast the spring increase is about March, the phytoplankton
flowering may occur earlier; for example, Ccmover (1956) and Riley
(1952) found an increase in early February in Long Island Sound and
Block Island Sound, and Fish (1925) believes that at Woods Hole the
increase is as early as December. This earlj flowering may depend
partly on the sheltering of waters in these areas. Certainly the timing of
the increase is not entirely associated with latitude. Thus Riley (1957)
recorded for the North Sargasso Sea (latitude :35"N) a small diatom increase as late as April and this was confirmed by Hulburt et al. (1 960)
off Bermuda. However, Menzel and Ryther (1960; 1961) find slightly
farther south that a winter flowering may occur in any month between
November and April. I n contrast to temperahe latitudes, in tropical