98
GORDON A. RILEY
although this is an over-simplification, for a detailed study of populations requires subdivision into several depth zones.
Finally there is an assemblage of benthic and epibenthic animals
and an associated bacterial flora. The benthic population of deep
ocean waters is not large, but it is probably about equal to the total
quantity in the sparsely inhabited bathypelagic zone.
The mid-depth zone properly includes the whole thermocline region.
Drawing an arbitrary dividing line at 300 m as was done above is an
artificiality imposed by the nature of the analyses. Physical oceanographic analyses were predicated on assumptions of a steady state and
had to be limited to waters in which there were no seasonal changes in
properties, and analyses of the upper 300 m cannot be partitioned with
enough precision to fill in the gaps in a very satisfactory way. There
is of course the further difficulty that the top of the thermocline varies
seasonally from 50 m or less to more than 150. However, with some
slight over-simplification a range of estimates of biological consumption
can be obtained for the depth range of 100-900 m, which constitutes
the major part of the mid-depth zone in this area. This depth range
will be examined briefly, and a more detailed balance sheet will be
drawn up later for the whole of the vertical column below 300 m.
A generalized estimate for oxygen consumption within this layer can
be derived from physical oceanographic analyses. The net decrease in
oxygen from the compensation depth to 300 m (item 2 above) plus the
decrease from 300-900 m (the same data used in compiling item 3) are
equivalent t o a total carbon consumption of 119 mg.m-2.day-1. For
reasons given below this figure may be too small.
A further estimate based upon respiratory rates requires an assumption about partitioning of zooplankton respiration within the upper
300 m. The total utilization of 110 mg C/day as described above is
assumed to be uniform with respect t o depth on the grounds that the
population is subject to diurnal migration, so that 73 mg can be allotted
to the 100-300 m depth range. To this is added 28 mg for animalrespiration bet,ween 300 and 900 m and an allotment for heterotrophs and
associated ultraplankton which could be as much as 70-100 mg if the
vertical variations in this segment of the population are comparable
.to those described by Pomeroy and Johannes (1968).
Vertical flux into this layer (Table X, p. 85) was estimated to be
109 mg C.m- 2.day- l, and the flux into deep water below was 9.5 mg ;
thus the loss within the layer was estimated to be about 100 mg. This
again is a crude and possibly minimal estimate. From the earlier discussion of this problem it will be apparent that as in the case of phytoplankton, the larger particles may be lost from the surface layer a t a
GORDON A. RILEY
although this is an over-simplification, for a detailed study of populations requires subdivision into several depth zones.
Finally there is an assemblage of benthic and epibenthic animals
and an associated bacterial flora. The benthic population of deep
ocean waters is not large, but it is probably about equal to the total
quantity in the sparsely inhabited bathypelagic zone.
The mid-depth zone properly includes the whole thermocline region.
Drawing an arbitrary dividing line at 300 m as was done above is an
artificiality imposed by the nature of the analyses. Physical oceanographic analyses were predicated on assumptions of a steady state and
had to be limited to waters in which there were no seasonal changes in
properties, and analyses of the upper 300 m cannot be partitioned with
enough precision to fill in the gaps in a very satisfactory way. There
is of course the further difficulty that the top of the thermocline varies
seasonally from 50 m or less to more than 150. However, with some
slight over-simplification a range of estimates of biological consumption
can be obtained for the depth range of 100-900 m, which constitutes
the major part of the mid-depth zone in this area. This depth range
will be examined briefly, and a more detailed balance sheet will be
drawn up later for the whole of the vertical column below 300 m.
A generalized estimate for oxygen consumption within this layer can
be derived from physical oceanographic analyses. The net decrease in
oxygen from the compensation depth to 300 m (item 2 above) plus the
decrease from 300-900 m (the same data used in compiling item 3) are
equivalent t o a total carbon consumption of 119 mg.m-2.day-1. For
reasons given below this figure may be too small.
A further estimate based upon respiratory rates requires an assumption about partitioning of zooplankton respiration within the upper
300 m. The total utilization of 110 mg C/day as described above is
assumed to be uniform with respect t o depth on the grounds that the
population is subject to diurnal migration, so that 73 mg can be allotted
to the 100-300 m depth range. To this is added 28 mg for animalrespiration bet,ween 300 and 900 m and an allotment for heterotrophs and
associated ultraplankton which could be as much as 70-100 mg if the
vertical variations in this segment of the population are comparable
.to those described by Pomeroy and Johannes (1968).
Vertical flux into this layer (Table X, p. 85) was estimated to be
109 mg C.m- 2.day- l, and the flux into deep water below was 9.5 mg ;
thus the loss within the layer was estimated to be about 100 mg. This
again is a crude and possibly minimal estimate. From the earlier discussion of this problem it will be apparent that as in the case of phytoplankton, the larger particles may be lost from the surface layer a t a