METHODS OF SAMPLING THE BENTHOS
227
There is of course a considerable time-lag in the bringing into use
of such improved methods of handling gear, as they may have to be
built in when the ship is constructed.
Some workers, when using fairly light gear in shallow water, have
lowered the grab on a rope, hauling in over a capstan. I n this way
rather exact control over the working of the grab is achieved, and i t
avoids pulling the grab out of the bottom before i t has closed. While
it is understandable that in trawling and dredging some skill is required
to obtain a good catch, it is a little disquieting to read that the same
is true of grab sampling. Thus Ursin (1954) has shown how, with
tirne, the volume of sediment in grab samples goes up as the skill
and experirncr of the crew improves. This is no doubt due to greater
sensitivity in breaking the grab out of the bottom. It is highly desirable
that such a source of variation be eliminated when new and improved
samplers are designed.
VIII. SAMPLINQ UNDER THE ICE
A number of workers have developed methods for sampling under
the ice in polar regions. I n the Antarctic, Hodgson (1907) devised a
technique by which a line was laid under water before surface ice had
formed. This was then used for towing a light trawl (D-net) to-and-fro,
samples being brought up through a hole in the ice. A similar technique
for dredging i s described by Thorson (1946) in Greenland waters.
In the same area Vibe (1950) has used a team of dogs for hauling up a
Petersen grab through a hole in the ice, and Ellis (1960) illustrates a
small grab being used through a break in the ice, in Canada. Peckham
(1964) describes observations on the sea floor and on the undersurface
of the ice made by free-diving, the water being entered through a hole
in the ice.
Thorson (1 946) illustrates a hut built, over a hole dug through the
ice. From this, plankton hauls were made during the winter. Such
a method if used for bottom-sampling might result in repetitive
sampling at exactly the same spot. This problem would not arise if
the ice were drifting and this fact enabled Tressler and Ommundsen
(1 962) to take a series of bottom samples in about 580 m in McMurdo
Sound, Antarctica. An insulated hut was built over a square hole, the
sides of which were lined, and through the hole various instrumentu
could be lowered on a light wire suspended from an A-frame and
worked by a small electric winch (Fig. 31). A small corer (the Phleger
corer, weighing 16 kg) gave disappointing results on the hard bottom,
and a small orange-peel dredge also failed to take good samples.
Finally a Petersen grab weighing 36 kg waa used with some success.
227
There is of course a considerable time-lag in the bringing into use
of such improved methods of handling gear, as they may have to be
built in when the ship is constructed.
Some workers, when using fairly light gear in shallow water, have
lowered the grab on a rope, hauling in over a capstan. I n this way
rather exact control over the working of the grab is achieved, and i t
avoids pulling the grab out of the bottom before i t has closed. While
it is understandable that in trawling and dredging some skill is required
to obtain a good catch, it is a little disquieting to read that the same
is true of grab sampling. Thus Ursin (1954) has shown how, with
tirne, the volume of sediment in grab samples goes up as the skill
and experirncr of the crew improves. This is no doubt due to greater
sensitivity in breaking the grab out of the bottom. It is highly desirable
that such a source of variation be eliminated when new and improved
samplers are designed.
VIII. SAMPLINQ UNDER THE ICE
A number of workers have developed methods for sampling under
the ice in polar regions. I n the Antarctic, Hodgson (1907) devised a
technique by which a line was laid under water before surface ice had
formed. This was then used for towing a light trawl (D-net) to-and-fro,
samples being brought up through a hole in the ice. A similar technique
for dredging i s described by Thorson (1946) in Greenland waters.
In the same area Vibe (1950) has used a team of dogs for hauling up a
Petersen grab through a hole in the ice, and Ellis (1960) illustrates a
small grab being used through a break in the ice, in Canada. Peckham
(1964) describes observations on the sea floor and on the undersurface
of the ice made by free-diving, the water being entered through a hole
in the ice.
Thorson (1 946) illustrates a hut built, over a hole dug through the
ice. From this, plankton hauls were made during the winter. Such
a method if used for bottom-sampling might result in repetitive
sampling at exactly the same spot. This problem would not arise if
the ice were drifting and this fact enabled Tressler and Ommundsen
(1 962) to take a series of bottom samples in about 580 m in McMurdo
Sound, Antarctica. An insulated hut was built over a square hole, the
sides of which were lined, and through the hole various instrumentu
could be lowered on a light wire suspended from an A-frame and
worked by a small electric winch (Fig. 31). A small corer (the Phleger
corer, weighing 16 kg) gave disappointing results on the hard bottom,
and a small orange-peel dredge also failed to take good samples.
Finally a Petersen grab weighing 36 kg waa used with some success.