28
GORDON A. RILEY
concentrate small particles in shear zones-vertical convective movements in the surface layer and horizontal shear zones in the thermocline-and that zooplankton tends to congregate in gradients. Interest
in this problem is giving rise t o incraasingly sophisticated devices for
examining micro-distribution of plankton. However, at the present
time there is still little quantitative information on the physical dimensions of these loci of abundance or the absolute magnitude of the
concentrations.
The temperature-depth curves given by Lovett (1968) indicated
that layering decreased with depth in the main thermocline. Deviations
from the mean gradient were small, below 1 000 m, but were detectable
t o a depth of about 2 000 m. Tait and Howe (1968) found quite distinct
layering to a depth of 1500 m in the vicinity of the Mediterranean
outflow.
The writer is indebted to Henry Stommel and W. F. Simmons for
permission to examine unpublished records of a similar sort which were
taken with a Salinity-Temperature-Depth recorder in the Sargasso Sea.
On two occasions the instrument was raised and lowered continuously
between 1 000 and 1 200 m, more or less, for a period of about half an
hour, while the ship drifted freely. Marked layering was observed,
including temperature inversions. The same pattern was repeated with
only minor differences throughout each half-hour period, indicating
that the discontinuities extended horizontally for some distance,
although their true size remains an open question. A single lowering
at another station to a depth of about 1 900 m showed irregularities in
temperature structure throughout the column, although the amount of
variation in the gradient decreased with depth. There was virtually no
variation in the salinity gradient below 1 000 m.
Paramonov et al. (1966) measured optical characteristics of the
water column as determined by lowering an instrument which bore a
fixed light source and a photocell and hence was able to determine
vertical variation in optical attenuation as the instrument was lowered
through water. Theoretically the attenuation would include both
absorption by dissolved materials and absorption and scattering by
particles ; however, the effect of particles is likely to be the dominant
feature in deep water and should provide a semi-quantitative indication
of variations in particulate organic matter. These authors found that
there were pronounced variations in attenuation in the surface layer
and in the main thermocline. I n the deep ocean there were no sharp
peaks. Minor variations were found, but they were gradual changes
in the level of the attenuation coefficient rather than sudden shifts.
Thus there is considerable likelihood that the thermal structure of
GORDON A. RILEY
concentrate small particles in shear zones-vertical convective movements in the surface layer and horizontal shear zones in the thermocline-and that zooplankton tends to congregate in gradients. Interest
in this problem is giving rise t o incraasingly sophisticated devices for
examining micro-distribution of plankton. However, at the present
time there is still little quantitative information on the physical dimensions of these loci of abundance or the absolute magnitude of the
concentrations.
The temperature-depth curves given by Lovett (1968) indicated
that layering decreased with depth in the main thermocline. Deviations
from the mean gradient were small, below 1 000 m, but were detectable
t o a depth of about 2 000 m. Tait and Howe (1968) found quite distinct
layering to a depth of 1500 m in the vicinity of the Mediterranean
outflow.
The writer is indebted to Henry Stommel and W. F. Simmons for
permission to examine unpublished records of a similar sort which were
taken with a Salinity-Temperature-Depth recorder in the Sargasso Sea.
On two occasions the instrument was raised and lowered continuously
between 1 000 and 1 200 m, more or less, for a period of about half an
hour, while the ship drifted freely. Marked layering was observed,
including temperature inversions. The same pattern was repeated with
only minor differences throughout each half-hour period, indicating
that the discontinuities extended horizontally for some distance,
although their true size remains an open question. A single lowering
at another station to a depth of about 1 900 m showed irregularities in
temperature structure throughout the column, although the amount of
variation in the gradient decreased with depth. There was virtually no
variation in the salinity gradient below 1 000 m.
Paramonov et al. (1966) measured optical characteristics of the
water column as determined by lowering an instrument which bore a
fixed light source and a photocell and hence was able to determine
vertical variation in optical attenuation as the instrument was lowered
through water. Theoretically the attenuation would include both
absorption by dissolved materials and absorption and scattering by
particles ; however, the effect of particles is likely to be the dominant
feature in deep water and should provide a semi-quantitative indication
of variations in particulate organic matter. These authors found that
there were pronounced variations in attenuation in the surface layer
and in the main thermocline. I n the deep ocean there were no sharp
peaks. Minor variations were found, but they were gradual changes
in the level of the attenuation coefficient rather than sudden shifts.
Thus there is considerable likelihood that the thermal structure of