140
HOBINA B. SCHOLES AND J. M. SHEWAN
regions a i d similar results wcre obtained in the Atlantic along 30°W,
the parallel along which the populations were found to be particularly
low in the Greenland Sea and Arctic Ocean. On the other hand, in the
Norwcgian Sea the hcterotrophic population was higher than in the
corresponding latitude along the 3O"W parallel. The more northerly
areas in this sea had lower counts than the southerly areas possibly
due to the effects of the Gulf Stream. All the data clearly demonstrate
that the heterotrophic population of the World's oceans is greatest in
the equatorial regions and decreases with distance towards the Poles
(Tablc 111). It is intercsting to note that with plant and animal life
in the sea the reverse seems to be the case. According to Kriss (1963),
this is due to the fact that the organic matter available in the polar
regions is not as conducive to the growth of heterotrophs as it is in
equatorial waters. It must also he remembered that the overall picture
given above may well be qualified at specific stations where proximity
to land, currents, seasonal and other factors may operate ; nor does it
specify the vertical distribution at various stations.
B. Vertical distribution
From Table 111, prepared from data obtained by Kriss and his
co-workers (1963), it will be noted that there appears to be no regularity
governing vertical distribution. As Kriss himself states, " If one prepares curves of vertical distribution of the heterotrophic concentration
at each station they will prove quite irregular and this will apply not
only to deep waters but also to the upper layers from 0 to 100 metres,
and for which ZoBcll (1946) produced quite a characteristic curve. The
features of the vertical distribution of heterotrophs at each station
are its focal character, steep gradients in the density of microbial
populations, increasing or decreasing from one level to another." It is
clear, therefore, that the oft-quoted diagrams of ZoBell's (1946)
showing the vertical distribution of heterotrophs in the sea apply
specifically to the areaa off California investigated by him and the increases in number in the 25- to 50-m zone may well be related, as ZOBell suggests, to intensity of sunlight, Kriss (1963) has shown that an
increase in the microbial population at certain levels is.due to hydrological phenomena such aa the convergence of water mmses of different
origin and demonstrates this by extending Butkevich's (1932, 1938)
observation in the polar area where it is known that a layer of water of
Atlantic Ocean origin penetrates the Arctic Ocean. Microbiological
counts indicate a sharp increase in the population at 900 and 1000 m,
i.e. at the upper and lower interfaces of this intrusive current (See
Fig. 2).
HOBINA B. SCHOLES AND J. M. SHEWAN
regions a i d similar results wcre obtained in the Atlantic along 30°W,
the parallel along which the populations were found to be particularly
low in the Greenland Sea and Arctic Ocean. On the other hand, in the
Norwcgian Sea the hcterotrophic population was higher than in the
corresponding latitude along the 3O"W parallel. The more northerly
areas in this sea had lower counts than the southerly areas possibly
due to the effects of the Gulf Stream. All the data clearly demonstrate
that the heterotrophic population of the World's oceans is greatest in
the equatorial regions and decreases with distance towards the Poles
(Tablc 111). It is intercsting to note that with plant and animal life
in the sea the reverse seems to be the case. According to Kriss (1963),
this is due to the fact that the organic matter available in the polar
regions is not as conducive to the growth of heterotrophs as it is in
equatorial waters. It must also he remembered that the overall picture
given above may well be qualified at specific stations where proximity
to land, currents, seasonal and other factors may operate ; nor does it
specify the vertical distribution at various stations.
B. Vertical distribution
From Table 111, prepared from data obtained by Kriss and his
co-workers (1963), it will be noted that there appears to be no regularity
governing vertical distribution. As Kriss himself states, " If one prepares curves of vertical distribution of the heterotrophic concentration
at each station they will prove quite irregular and this will apply not
only to deep waters but also to the upper layers from 0 to 100 metres,
and for which ZoBcll (1946) produced quite a characteristic curve. The
features of the vertical distribution of heterotrophs at each station
are its focal character, steep gradients in the density of microbial
populations, increasing or decreasing from one level to another." It is
clear, therefore, that the oft-quoted diagrams of ZoBell's (1946)
showing the vertical distribution of heterotrophs in the sea apply
specifically to the areaa off California investigated by him and the increases in number in the 25- to 50-m zone may well be related, as ZOBell suggests, to intensity of sunlight, Kriss (1963) has shown that an
increase in the microbial population at certain levels is.due to hydrological phenomena such aa the convergence of water mmses of different
origin and demonstrates this by extending Butkevich's (1932, 1938)
observation in the polar area where it is known that a layer of water of
Atlantic Ocean origin penetrates the Arctic Ocean. Microbiological
counts indicate a sharp increase in the population at 900 and 1000 m,
i.e. at the upper and lower interfaces of this intrusive current (See
Fig. 2).