PLANKTON IN NITROGEN AND PHOSPHORUS CYCLES
177
phytoplankton ; and dissolved organic phosphorus was considered to
be formed, at any depth, either by excretion or by the decomposition
of particulate phosphorus.
The phosphorus involved in the cycle : Inorganic P-t Particulate
P+ Dissolved Organic P-t Inorganic P could then be calculated as
(1) Decrease in phosphorus due to photosynthesis
= Inorgaiiic P loss - Inorganic P gain + Dissolvcd organic P loss
= 14.20 - 2-72 + 4.99 = 1647 mg-atoms P/m2.
(2) Organic phosphorus produced
= Particulate P increase (euphotic zone + below 50 m - Particulate
P loss + Dissolved organic P increase
= (8.18 + 7.34) -0.60 + 1.43 = 16.35 mg-atoms P/m2.
The agreement between the two values was within the analytical error.
The oxygen concentration in the upper 50 m increased by 41.8 l./m2,
while below 50 m and down to the uT level of 26.34, there was a decrease
of 14.6 l./m2. The increase in oxygen in the euphotic zone gave only a
minimal estimate of photosynthetic oxygen production because on both
occasions the water was saturated with the gas and there would have
been a loss to the atmosphere. Ketchum and Corwin therefore used
the method of Redfield (1948) to calculate from their data a value of
the exchange coefficient of oxygen across the sea surface, and estimated
that 9.7 l./m2 of oxygen were lost from the surface t o the atmosphere
in the ten day period. Thus, the total oxygen production in the eupliotic
zone would have been 51.5 l./m2. This value, in conjunction with thc
phosphorus change of 16.47 mg-atoms/m2, leads to a A 0 :LIP ratio of
-279 : 1. For deeper water, where the oxygen consumption corresponded to a decrease in dissolved organic phosphorus of 4-61 mg-atoms/
m2, a ratio of -282 : 1 was obtained. Both ratios are in good agreement
with the geiicrally accepted value of -276:l (see Section 111).
The dissolved organic phosphate (1.43 mg-atoms/m2) in the upper
25 m may have been excreted by zooplankton or released as extracellular products by the phytoplankton. However, as remineralization
probably occurs independently of depth and there was a decrease of
dissolved organic phosphorus between 25 m and 150 m of 4.99 mgatoms/m2 (average 0.04 mg-atoms/m3), it is likely that a further 1 mgatom/m2 of dissolved organic phosphorus was produced in the upper
25 m, increasing the total phosphorus cycled in the 10 day period to
17.40 mg-atoms/m2.
mg-atoms P/m3/day
meant that the rate of phosphorus assimilation by the plankton was
The mean regeneration rate of 4.0 x
177
phytoplankton ; and dissolved organic phosphorus was considered to
be formed, at any depth, either by excretion or by the decomposition
of particulate phosphorus.
The phosphorus involved in the cycle : Inorganic P-t Particulate
P+ Dissolved Organic P-t Inorganic P could then be calculated as
(1) Decrease in phosphorus due to photosynthesis
= Inorgaiiic P loss - Inorganic P gain + Dissolvcd organic P loss
= 14.20 - 2-72 + 4.99 = 1647 mg-atoms P/m2.
(2) Organic phosphorus produced
= Particulate P increase (euphotic zone + below 50 m - Particulate
P loss + Dissolved organic P increase
= (8.18 + 7.34) -0.60 + 1.43 = 16.35 mg-atoms P/m2.
The agreement between the two values was within the analytical error.
The oxygen concentration in the upper 50 m increased by 41.8 l./m2,
while below 50 m and down to the uT level of 26.34, there was a decrease
of 14.6 l./m2. The increase in oxygen in the euphotic zone gave only a
minimal estimate of photosynthetic oxygen production because on both
occasions the water was saturated with the gas and there would have
been a loss to the atmosphere. Ketchum and Corwin therefore used
the method of Redfield (1948) to calculate from their data a value of
the exchange coefficient of oxygen across the sea surface, and estimated
that 9.7 l./m2 of oxygen were lost from the surface t o the atmosphere
in the ten day period. Thus, the total oxygen production in the eupliotic
zone would have been 51.5 l./m2. This value, in conjunction with thc
phosphorus change of 16.47 mg-atoms/m2, leads to a A 0 :LIP ratio of
-279 : 1. For deeper water, where the oxygen consumption corresponded to a decrease in dissolved organic phosphorus of 4-61 mg-atoms/
m2, a ratio of -282 : 1 was obtained. Both ratios are in good agreement
with the geiicrally accepted value of -276:l (see Section 111).
The dissolved organic phosphate (1.43 mg-atoms/m2) in the upper
25 m may have been excreted by zooplankton or released as extracellular products by the phytoplankton. However, as remineralization
probably occurs independently of depth and there was a decrease of
dissolved organic phosphorus between 25 m and 150 m of 4.99 mgatoms/m2 (average 0.04 mg-atoms/m3), it is likely that a further 1 mgatom/m2 of dissolved organic phosphorus was produced in the upper
25 m, increasing the total phosphorus cycled in the 10 day period to
17.40 mg-atoms/m2.
mg-atoms P/m3/day
meant that the rate of phosphorus assimilation by the plankton was
The mean regeneration rate of 4.0 x