PARTICULATE ORGANIC MATTER I N SEA WATER
67
Direct measurements clearly are needed. The present section will
deal with a few measurements that have been made on naturally
occurring surface and deep water particulate matter and experimental
preparations. The quantity of data is not large, but it is enough for
present purposes.
2. Methods
This work was done with an inverted microscope, using a counting
cell 1-5 cm in diameter and 4.5 cm high, which was merely a lucite
tube with a cover slip cemented to the bottom. Lucite was used because
it has a lower rate of thermal conductivity than glass, and it is important in experiments of this sort to reduce convective mixing as much
as possible. A cover slip was laid on top to inhibit evaporative cooling.
I n the
beginning an attempt was made to follow the method used by Smayda
and Boleyn (1965, 1966a and b) to measure the sinking rate of diatoms.
These investigators filled their tubes with sea water of a salinity of 32%,
and introduced a diatom population at the surface in a medium of 30%,.
Initially all of the diatoms were within the upper boundary layer, and
the bottom of the cell was then scanned at intervals thereafter to determine the rate of sinking from surface to bottom.
There were practica1 difficulties in applying this method in the
present case. I n order to get enough material for a good count, the
particulate matter had to be concentrated into a small volume. Under
these conditions the aggregates tended to coalesce, and the sizefrequency distribution was unrealistic. Thus it was necessary to use
whole water samples or slightly concentrated ones and to fill the entire
cell with uniformly mixed material. The method sacrificed any possibility of determining sinking rates of individual particles but permitted
a statistical estimate of the average rate of passage of the various kinds
of particles through a mean vertical path.
Repeated examinations were made of the same area on the bottom
of the cell, consisting of a strip 0-3 mm wide and 10 mm long, under a
magnification of x 300. The ocular grid that was used as a guide in
counting was subdivided into smaller squares equivalent to 30 p and
6 p, which served as convenient references for estimating particle size.
The categories that were recorded were flakes, four size ranges of
amorphous aggregates, and miscellaneous particles in the size range of
2-6 p. The character of the latter could not be clearly distinguished in
all cases. Phytoplankton and bacteria were excluded, of course, but
the less structured material which was counted probably included
Preparation of the material presented some problems.
67
Direct measurements clearly are needed. The present section will
deal with a few measurements that have been made on naturally
occurring surface and deep water particulate matter and experimental
preparations. The quantity of data is not large, but it is enough for
present purposes.
2. Methods
This work was done with an inverted microscope, using a counting
cell 1-5 cm in diameter and 4.5 cm high, which was merely a lucite
tube with a cover slip cemented to the bottom. Lucite was used because
it has a lower rate of thermal conductivity than glass, and it is important in experiments of this sort to reduce convective mixing as much
as possible. A cover slip was laid on top to inhibit evaporative cooling.
I n the
beginning an attempt was made to follow the method used by Smayda
and Boleyn (1965, 1966a and b) to measure the sinking rate of diatoms.
These investigators filled their tubes with sea water of a salinity of 32%,
and introduced a diatom population at the surface in a medium of 30%,.
Initially all of the diatoms were within the upper boundary layer, and
the bottom of the cell was then scanned at intervals thereafter to determine the rate of sinking from surface to bottom.
There were practica1 difficulties in applying this method in the
present case. I n order to get enough material for a good count, the
particulate matter had to be concentrated into a small volume. Under
these conditions the aggregates tended to coalesce, and the sizefrequency distribution was unrealistic. Thus it was necessary to use
whole water samples or slightly concentrated ones and to fill the entire
cell with uniformly mixed material. The method sacrificed any possibility of determining sinking rates of individual particles but permitted
a statistical estimate of the average rate of passage of the various kinds
of particles through a mean vertical path.
Repeated examinations were made of the same area on the bottom
of the cell, consisting of a strip 0-3 mm wide and 10 mm long, under a
magnification of x 300. The ocular grid that was used as a guide in
counting was subdivided into smaller squares equivalent to 30 p and
6 p, which served as convenient references for estimating particle size.
The categories that were recorded were flakes, four size ranges of
amorphous aggregates, and miscellaneous particles in the size range of
2-6 p. The character of the latter could not be clearly distinguished in
all cases. Phytoplankton and bacteria were excluded, of course, but
the less structured material which was counted probably included
Preparation of the material presented some problems.