WWPkLIlk2 d D "HE PRODUCTION OF FtbE
967
B. The part played by nutrients in an upwelling syslent
The high production in thc subtropical upwelling arcas and in the
Antarctic is often attributed to the associated presence of high nutrients
which have reached the surface from below in the upwelled water
(Hentschel and Wattenberg, 1930 ; Deacon, 1937). As nutrients become
reduced, the algal reproductive rate may decline; Riley (1946), on the
basis of an experiment by Ketchum (1939), suggested a level of 0.55 pg
atoms PO,.P/l. below which the algal reproductive rate becomes reduced. Ketchum's experiment showed that the quantity of algae
produced was proportional to the quantity of phosphorus available. A
repetition of this experiment confirmed this result, but showed that the
rate at which the algae were produced was unaffected by the nutrient
concentration, and that the quantities produced were reached at
different times (Cushing, 1955). The plastic bag experiments in the
Pacific made by McAllister et al. (1960) and Antia et al. (1963) show that
such a nutrient limit must be at a very low level, and in nutrients other
than phosphorus, as well as phosphorus. A production cycle in the
North Sea was shown to be completed with little reduction in nitrate,
phosphate or silicate and no reduction in algal reproductive rate
(Cushing, 1963; Cushing and Nicholson, 1963) ; so the decline in algal
numbers must have been caused by grazing. This does not mean that
nutrient lack never limits production, but that it works as a fail-safe
device, rather than as a universal limit ; if grazing animals are absent,
production must stop when the nutrients run out. So the very high
values of nutrients found in the Antarctic and all over the upwelling
areas do not limit production, nor can they accelerate it. The persistence
of production in an upwelling area is due not to the presence of excess
nutrient, but to the persistent addition of living material from a continuous band of temperate production cycles in the upwelling areas.
A remarkable point about the upwelling areas is that phosphorus
and zooplankton are positively correlated (Hentschel and Wattenberg,
1930; Holmes et al., 1957; Reid, 1962b) across the south Atlantic and
the whole Pacific. Figure 5 from Reid, 196213 shows the distribution in
phosphorus and in zooplankton. Figure 5A shows the distribution of
phosphate-phosphorus at 100 m in the Pacific and Fig. 5B shows that
of zooplankton hauled from about 200 m to the surface. The phosphorus
distribution shows high values in the South Equatorial Current from
the Peru Coastal Current almost to the Antipodes. The North Equatorial Current is shown in the same way as an arm reaching out westward from the eastern tropical Pacific. Between the two equatorial
currents is an area of lower density in phosphorus which may indicate
967
B. The part played by nutrients in an upwelling syslent
The high production in thc subtropical upwelling arcas and in the
Antarctic is often attributed to the associated presence of high nutrients
which have reached the surface from below in the upwelled water
(Hentschel and Wattenberg, 1930 ; Deacon, 1937). As nutrients become
reduced, the algal reproductive rate may decline; Riley (1946), on the
basis of an experiment by Ketchum (1939), suggested a level of 0.55 pg
atoms PO,.P/l. below which the algal reproductive rate becomes reduced. Ketchum's experiment showed that the quantity of algae
produced was proportional to the quantity of phosphorus available. A
repetition of this experiment confirmed this result, but showed that the
rate at which the algae were produced was unaffected by the nutrient
concentration, and that the quantities produced were reached at
different times (Cushing, 1955). The plastic bag experiments in the
Pacific made by McAllister et al. (1960) and Antia et al. (1963) show that
such a nutrient limit must be at a very low level, and in nutrients other
than phosphorus, as well as phosphorus. A production cycle in the
North Sea was shown to be completed with little reduction in nitrate,
phosphate or silicate and no reduction in algal reproductive rate
(Cushing, 1963; Cushing and Nicholson, 1963) ; so the decline in algal
numbers must have been caused by grazing. This does not mean that
nutrient lack never limits production, but that it works as a fail-safe
device, rather than as a universal limit ; if grazing animals are absent,
production must stop when the nutrients run out. So the very high
values of nutrients found in the Antarctic and all over the upwelling
areas do not limit production, nor can they accelerate it. The persistence
of production in an upwelling area is due not to the presence of excess
nutrient, but to the persistent addition of living material from a continuous band of temperate production cycles in the upwelling areas.
A remarkable point about the upwelling areas is that phosphorus
and zooplankton are positively correlated (Hentschel and Wattenberg,
1930; Holmes et al., 1957; Reid, 1962b) across the south Atlantic and
the whole Pacific. Figure 5 from Reid, 196213 shows the distribution in
phosphorus and in zooplankton. Figure 5A shows the distribution of
phosphate-phosphorus at 100 m in the Pacific and Fig. 5B shows that
of zooplankton hauled from about 200 m to the surface. The phosphorus
distribution shows high values in the South Equatorial Current from
the Peru Coastal Current almost to the Antipodes. The North Equatorial Current is shown in the same way as an arm reaching out westward from the eastern tropical Pacific. Between the two equatorial
currents is an area of lower density in phosphorus which may indicate