206
N. A . tIOIAME
ments in ease of operation, but, the sampling area is rather small for
investigations of the macrofauna.
This may be a convenient point to refer to the orange-peel grab
(Fig. 23), an instrument usc.d mainly in the United States for quantitative sampling. It is commercially available in different sizes in the
U.S.A., and consists of four curved jaws which close together to enclose
a hemisphere of sediment. The top of the apparatus may be closed
by a canvas skirt to minimize washing out of the sample. Thorson
(1957a) is critical of this instrument as a quantitative sampler, his
main objection being the washing out of material both from the
surface of the sample and between jaws which may not close properly
in certain soils, and the difficulty in ascertaining the surface area
sampled. Somtb of Thorson’s objections have, however, been countered
by Reish (l!).Wb). Certainly it seems to be suitable for sampling the
muddy deposits off California (Hartman, 1955), but in sandy and stony
grounds its rffectiveness is more questionable.
The retention of a sample within a wide-mouth
coring tube apparently presents considerable difficulties. Flap-valves
as used in geological coring tubes are usually impracticable, although
the Enequist (1941) sampler is closed by flaps on either side of the
mouth (Fig. 13). In the Otto Petterson (1928) sampler the square tube
is closed by a flexible sheet of thin copper with cutting edge which is
pulled horizontally across the mouth of the tube. It is doubtful if
this could function for long without damage except in soft sediments
where stones and shells were absent.
It is quite possible, however, to bring up an almost intact core if
the top of the tube is sealed and the tube turned over as it is pulled
out of the bottom. This principle is embodied in Knudsen’s (1927)
sampler, and was also employed in a suction sampler described by
Holme (1953, p. 11). After inversion the open end of the tube could
if necessary be sealed by a flap.
3. Releaee mechanisms
The usual release mechanism consist8 of a hook which H U I J P O ~ ~ B
the instrument in the “ open ” position (Fig. 12) while it is lowered.
When the cable slackens, the hook falls and disconnects so that on
hoisting the strain is transferred to a mechttnism by which the sampler
is closed before it leaves the bottom. Such a method is employed on
the Petersen and van Veen grabs, and on Holme’s sampler. It is quite
reliable in calm water, but if the ship is rolling it is possible for the
cable to slacken and the release to be triggered before reaching bottom.
To counteract this tendency Petersen (1918) fitted a small parachute
Coring tubes.
N. A . tIOIAME
ments in ease of operation, but, the sampling area is rather small for
investigations of the macrofauna.
This may be a convenient point to refer to the orange-peel grab
(Fig. 23), an instrument usc.d mainly in the United States for quantitative sampling. It is commercially available in different sizes in the
U.S.A., and consists of four curved jaws which close together to enclose
a hemisphere of sediment. The top of the apparatus may be closed
by a canvas skirt to minimize washing out of the sample. Thorson
(1957a) is critical of this instrument as a quantitative sampler, his
main objection being the washing out of material both from the
surface of the sample and between jaws which may not close properly
in certain soils, and the difficulty in ascertaining the surface area
sampled. Somtb of Thorson’s objections have, however, been countered
by Reish (l!).Wb). Certainly it seems to be suitable for sampling the
muddy deposits off California (Hartman, 1955), but in sandy and stony
grounds its rffectiveness is more questionable.
The retention of a sample within a wide-mouth
coring tube apparently presents considerable difficulties. Flap-valves
as used in geological coring tubes are usually impracticable, although
the Enequist (1941) sampler is closed by flaps on either side of the
mouth (Fig. 13). In the Otto Petterson (1928) sampler the square tube
is closed by a flexible sheet of thin copper with cutting edge which is
pulled horizontally across the mouth of the tube. It is doubtful if
this could function for long without damage except in soft sediments
where stones and shells were absent.
It is quite possible, however, to bring up an almost intact core if
the top of the tube is sealed and the tube turned over as it is pulled
out of the bottom. This principle is embodied in Knudsen’s (1927)
sampler, and was also employed in a suction sampler described by
Holme (1953, p. 11). After inversion the open end of the tube could
if necessary be sealed by a flap.
3. Releaee mechanisms
The usual release mechanism consist8 of a hook which H U I J P O ~ ~ B
the instrument in the “ open ” position (Fig. 12) while it is lowered.
When the cable slackens, the hook falls and disconnects so that on
hoisting the strain is transferred to a mechttnism by which the sampler
is closed before it leaves the bottom. Such a method is employed on
the Petersen and van Veen grabs, and on Holme’s sampler. It is quite
reliable in calm water, but if the ship is rolling it is possible for the
cable to slacken and the release to be triggered before reaching bottom.
To counteract this tendency Petersen (1918) fitted a small parachute
Coring tubes.