100
GORDON A. HILEY
Correction of the figures for advection would require adjustments in
coefficients of eddy diffusivity in order t o maintain a conservative
balance of salt, and this would lead in turn to alterations in estimates
of biological rates of change. Possibly the alterations would be quite
local, in association with major deep water currents, or they might be
more general. Intuitive methods are not equal to the problem, but
conceivably all of the mid-depth and deep water biological rates of
change that have been listed here should be doubled, more or less. I n
deep water the values are so small that no conclusions would be seriously altered. I n the mid-depth region from 100 to 900 m it makes
some difference as to whether consumption is one-third or two-thirds
of the total surface production.
This discussion makes it quite apparent that the writer does not
subscribe to the viewpoint expressed by Menzel and Ryther (1968a),
who regarded the oxygen distribution in lower mid-depths and deep
water as being essentially conservative. Their hypothesis seems to be
that oxygen deficits develop in the upper reaches of the thermocline
and are translated horizontally and to greater depths by isentropic
mixing, and apparently they regarded the whole of the oxygen minimum layer of the Atlantic Ocean as having been derived from Equatorial upwelling areas off Africa. Reasons why this conclusion is
unacceptable have been presented earlier. Their conclusion that
oxygen consumption in deeper water is conservative requires further
discussion.
They analyzed the distribution of oxygen along the axis of the
Antarctic Intermediate water in the South Atlantic, a water mass
lying just above the upper boundary of the deep water that is under
present consideration. In their north-south profile, which extended
from approximately 10’ to 36’5, there was a decrease in oxygen of
about 2.65 ml/litre from south to north. They used the so-called
This
method assumes that mixing takes place only along the axis, so that
the salinity at any intermediate point can be determined as percentage
mixtures of water at the two ends. These percentages are then applied
to the two end values for oxygen to determine intermediate concentrations. Menzel and Ryther found that these more or less agreed
with observed values and concluded that oxygen is a conservative
property.
Earlier Riley (1951) had obtained an estimate for annual oxygen
consumption of about 0.01 ml/litre in this water mass, a modest
amount although considerably larger than the deep water average
quoted above. However, even this small rate of change could lead t o
core ” method to analyze oxygen at intermediate points.
6 6
GORDON A. HILEY
Correction of the figures for advection would require adjustments in
coefficients of eddy diffusivity in order t o maintain a conservative
balance of salt, and this would lead in turn to alterations in estimates
of biological rates of change. Possibly the alterations would be quite
local, in association with major deep water currents, or they might be
more general. Intuitive methods are not equal to the problem, but
conceivably all of the mid-depth and deep water biological rates of
change that have been listed here should be doubled, more or less. I n
deep water the values are so small that no conclusions would be seriously altered. I n the mid-depth region from 100 to 900 m it makes
some difference as to whether consumption is one-third or two-thirds
of the total surface production.
This discussion makes it quite apparent that the writer does not
subscribe to the viewpoint expressed by Menzel and Ryther (1968a),
who regarded the oxygen distribution in lower mid-depths and deep
water as being essentially conservative. Their hypothesis seems to be
that oxygen deficits develop in the upper reaches of the thermocline
and are translated horizontally and to greater depths by isentropic
mixing, and apparently they regarded the whole of the oxygen minimum layer of the Atlantic Ocean as having been derived from Equatorial upwelling areas off Africa. Reasons why this conclusion is
unacceptable have been presented earlier. Their conclusion that
oxygen consumption in deeper water is conservative requires further
discussion.
They analyzed the distribution of oxygen along the axis of the
Antarctic Intermediate water in the South Atlantic, a water mass
lying just above the upper boundary of the deep water that is under
present consideration. In their north-south profile, which extended
from approximately 10’ to 36’5, there was a decrease in oxygen of
about 2.65 ml/litre from south to north. They used the so-called
This
method assumes that mixing takes place only along the axis, so that
the salinity at any intermediate point can be determined as percentage
mixtures of water at the two ends. These percentages are then applied
to the two end values for oxygen to determine intermediate concentrations. Menzel and Ryther found that these more or less agreed
with observed values and concluded that oxygen is a conservative
property.
Earlier Riley (1951) had obtained an estimate for annual oxygen
consumption of about 0.01 ml/litre in this water mass, a modest
amount although considerably larger than the deep water average
quoted above. However, even this small rate of change could lead t o
core ” method to analyze oxygen at intermediate points.
6 6