PARTICULATE ORGANIC MATTER IN SEA WATEK
85
where S is the mean sinking rate of organic carbon C, A is the coefficient
of vertical eddy diffusivity, and AC/Az is the mean vertical gradient in
organic carbon in the depth range in question.
The mean sinking rate S is assumed to be 1 m/day at the top of
the layer. This is approximately the observed value in experiments
with inshore water and surface Slope Water. A sinking rate of 0.24
is postulated for the bottom of the layer. This again is obtained from
experiments on Slope Water, using mid-depth values and correcting
for a change in viscosity.
No
experimental observations are available for the area in question, and
there is no good way to make allowance for the possibility that the rate
of delivery of large particles may be enhanced by convective movement
or that there may be a significant quantity of small particles with a
negligible sinking rate.
Eddy coefficients are generally small in the thermocline. A value
of 1 cm2/sec is postulated for the upper part of the zone and 0.5 for
the lower boundary. The mean decrease in carbon content between
100 and 200 m is about 25 pg C/litre, and between 500 and 900 m it is
about 20 pg C/litre. These values are used to compute eddy flux. The
calculation is carried out in the c.g.s. system, but results are translated
into terms of daily flux in Table X.
These obviously are crude estimates.
TABLE X. COMPUTATION OF VERTICAL FLUX OF CARBON IN THE
TRANSITION ZONE (WG C.CM-~.DAY -l) AND CARBON Loss WITHIN
THE LAYER ( P G C.LITRE DAY - l ) . FOR FURTHER DETAILS SEE TEXT
100 rn
900 rn
S ( W a y )
1
0.25
A(cm2/sec)
1
0.5
cs
10
0.75
Total Flux (F)
10.9
0.95
Carbon loss
0.12
Eddy Flux
0.9
0.2
The total flux F in the table is in terms of pg C passing downward
through a horizontal area of 1 cm2 in a day. It will be noted here that
the eddy flux is relatively insignificant and might have been omitted ;
however, it could be important in areas where gradients in organic
carbon are steeper. The difference in flux between the upper and lower
limits of the zone represents total carbon loss. This difference, divided
by the volume of water in which it occurs, gives an estimate of carbon
loss of 0.12 pg C.litre-l.day-l, which is shown as the last entry in the
A.H.B.-S
4
85
where S is the mean sinking rate of organic carbon C, A is the coefficient
of vertical eddy diffusivity, and AC/Az is the mean vertical gradient in
organic carbon in the depth range in question.
The mean sinking rate S is assumed to be 1 m/day at the top of
the layer. This is approximately the observed value in experiments
with inshore water and surface Slope Water. A sinking rate of 0.24
is postulated for the bottom of the layer. This again is obtained from
experiments on Slope Water, using mid-depth values and correcting
for a change in viscosity.
No
experimental observations are available for the area in question, and
there is no good way to make allowance for the possibility that the rate
of delivery of large particles may be enhanced by convective movement
or that there may be a significant quantity of small particles with a
negligible sinking rate.
Eddy coefficients are generally small in the thermocline. A value
of 1 cm2/sec is postulated for the upper part of the zone and 0.5 for
the lower boundary. The mean decrease in carbon content between
100 and 200 m is about 25 pg C/litre, and between 500 and 900 m it is
about 20 pg C/litre. These values are used to compute eddy flux. The
calculation is carried out in the c.g.s. system, but results are translated
into terms of daily flux in Table X.
These obviously are crude estimates.
TABLE X. COMPUTATION OF VERTICAL FLUX OF CARBON IN THE
TRANSITION ZONE (WG C.CM-~.DAY -l) AND CARBON Loss WITHIN
THE LAYER ( P G C.LITRE DAY - l ) . FOR FURTHER DETAILS SEE TEXT
100 rn
900 rn
S ( W a y )
1
0.25
A(cm2/sec)
1
0.5
cs
10
0.75
Total Flux (F)
10.9
0.95
Carbon loss
0.12
Eddy Flux
0.9
0.2
The total flux F in the table is in terms of pg C passing downward
through a horizontal area of 1 cm2 in a day. It will be noted here that
the eddy flux is relatively insignificant and might have been omitted ;
however, it could be important in areas where gradients in organic
carbon are steeper. The difference in flux between the upper and lower
limits of the zone represents total carbon loss. This difference, divided
by the volume of water in which it occurs, gives an estimate of carbon
loss of 0.12 pg C.litre-l.day-l, which is shown as the last entry in the
A.H.B.-S
4