PARTICULATE ORGANIC MATTER I N SEA WATER
89
Various estimates have been made of production and consumption
in near-surface waters, and by difference we can estimate the amount
of food available for deep water organisms, allowing the assumption
of total balance. Some attempts have also been made to evaluate deep
water consumption rates. These are of a lower order of validity, but
they deserve comparison with other items in the overall balance sheet.
Riley et al. (1965) developed this kind of balance sheet in connection
with studies of non-living particulate matter in the Sargasso Sea, with
particular emphasis on respiratory rates and food requirements of the
deepwater population. Four essentially independent analyses were
presented :
( 1 ) Menzel and Ryther (1960) measured C14 uptake by phytoplankton in the surface layer off Bermuda and found that the mean daily
production, averaged over a period of a year, was 200 mg C.m-2.dayThe same authors (1961) made quantitative collections of zooplankton
to a depth of 500 m, obtaining an average value of 1.08 g dry weight/m2.
The mean respiratory requirement was determined experimentally and
averaged 0.12 g C/g dry wt of zooplankton. Thus the total requirement
of zooplankton in the upper 500 m was estimated to be 130 mg C.m-2.
day-l. This leaves an excess of 70 mg C/day which might be available
to deep water organisms ; however, there are two ambiguities : (a) no
allowance is made for bacterial metabolism in the upper water, and
(b) part of the photosynthetic product may be liberated to the water
in dissolved form and hence is not measured as production by the C14
method. Thus there is some doubt as to whether the amount of food
materials available to populations in deep water might be more or less
than 70 mg.
(2) Riley (1957) used observed vertical gradients of oxygen and
computed eddy coefficients to estimate net organic production in the
upper 300 m of the Sargasso Sea. This method theoretically measures
the difference between oxygen production by phytoplankton and oxygen consumption by all components of the population. Hence it is free
of some of the difficulties mentioned in item ( l ) , but the method of
computation is indirect and is subject to considerable error. The results
indicated that net oxygen production between the surface and the
compensation depth was equivalent, on a mean annual basis, to 134 mg
C.m - 2.day- l. The net decrease from the compensation depth to 300 m
was 81 mg. The difference of 53 mg C.m-2.day-1 provides an estimate
of potential deep water consumption.
(3) Riley (1951) used similar but somewhat more complicated
methods to compute deep water oxygen consumption. This was a
generalized calculation for the central Atlantic basic and might be an
89
Various estimates have been made of production and consumption
in near-surface waters, and by difference we can estimate the amount
of food available for deep water organisms, allowing the assumption
of total balance. Some attempts have also been made to evaluate deep
water consumption rates. These are of a lower order of validity, but
they deserve comparison with other items in the overall balance sheet.
Riley et al. (1965) developed this kind of balance sheet in connection
with studies of non-living particulate matter in the Sargasso Sea, with
particular emphasis on respiratory rates and food requirements of the
deepwater population. Four essentially independent analyses were
presented :
( 1 ) Menzel and Ryther (1960) measured C14 uptake by phytoplankton in the surface layer off Bermuda and found that the mean daily
production, averaged over a period of a year, was 200 mg C.m-2.dayThe same authors (1961) made quantitative collections of zooplankton
to a depth of 500 m, obtaining an average value of 1.08 g dry weight/m2.
The mean respiratory requirement was determined experimentally and
averaged 0.12 g C/g dry wt of zooplankton. Thus the total requirement
of zooplankton in the upper 500 m was estimated to be 130 mg C.m-2.
day-l. This leaves an excess of 70 mg C/day which might be available
to deep water organisms ; however, there are two ambiguities : (a) no
allowance is made for bacterial metabolism in the upper water, and
(b) part of the photosynthetic product may be liberated to the water
in dissolved form and hence is not measured as production by the C14
method. Thus there is some doubt as to whether the amount of food
materials available to populations in deep water might be more or less
than 70 mg.
(2) Riley (1957) used observed vertical gradients of oxygen and
computed eddy coefficients to estimate net organic production in the
upper 300 m of the Sargasso Sea. This method theoretically measures
the difference between oxygen production by phytoplankton and oxygen consumption by all components of the population. Hence it is free
of some of the difficulties mentioned in item ( l ) , but the method of
computation is indirect and is subject to considerable error. The results
indicated that net oxygen production between the surface and the
compensation depth was equivalent, on a mean annual basis, to 134 mg
C.m - 2.day- l. The net decrease from the compensation depth to 300 m
was 81 mg. The difference of 53 mg C.m-2.day-1 provides an estimate
of potential deep water consumption.
(3) Riley (1951) used similar but somewhat more complicated
methods to compute deep water oxygen consumption. This was a
generalized calculation for the central Atlantic basic and might be an