222
N. A. HOLME
A. D. McIntyre informs ine that even in calm weather subsurface
currents can make work with the van Veen grab quite impossible.)
Under such conditions, apart from dredges, or the anchor-dredge,
oither the Aberdeen grab or Holme’s scoop-sampler may be the most
satisfactory.
4. Deep-sea sampling
Dredges and the Agassiz trawl have in the past been the normal
methods of deep-sea collecting, but in recent years some quantitative
work has been attempted.
Expericnce of deep-sea work with quantitative instruments is
limited, but on the Galathea expedition both Petersen and van Veen
grabs were used (Sparck, 1951, 1966). As reported by Thorson (1957a),
however, the van Veen grab was found “ unfit for work a t great ocean
depths as the standing waves or swell at the surface or deeper down
will act upon the levers so as to close the grab long before it hits the
bottom.” How often has a grab been condemned solely because its
release mechanism was faulty !
A grab especially designed for deep-sea work is the Okean grab of
Lisitsin and Udintsev (1965). With its improved release gear, and its
provisions for being lowcred at some speed, it may well become widely
used in the future.
Providing the sampler can be lowered a t a speed fast enough for
coiivenience and without daiiger of tripping the release, almost any
grab could be tricd in deep water. Mr. A. 1 ) . McIntyre informs me that
he has reccntly worked the Aberdeen grab at depths down to 3500 m
in the Indian Ocean. He emphasizt?~ the need to use the thinnest
practicable warp so that it is possible, by watching the accumulator
spring on the lowering davit, to detect when the grab (weighted to
100 kg) touches bottom and again when the strain is taken up to lift
it clear of the bottom.
To sun1 up-there is no instrument which takes really satisfactory
quantitative samples on sandy grounds under open-see conditions.
The choice of sampler will depend upon local conditions, but among
the most widely used are the van Veen and Aberdeen grabs for quantitative sampling ; underwatcr cameras ; and the anchor-dredge for
semi-quantitative work. Although widely used on muddy grounds,
the Petersen grab is not the best choice on a hard sandy bottom.
It is difficult to give a fair estimate of the orange-peel grab’s abilities
on sandy grounds; it appears to be not too satisfactory. I do not
know of any tests comparing the Okean grab with others in common
N. A. HOLME
A. D. McIntyre informs ine that even in calm weather subsurface
currents can make work with the van Veen grab quite impossible.)
Under such conditions, apart from dredges, or the anchor-dredge,
oither the Aberdeen grab or Holme’s scoop-sampler may be the most
satisfactory.
4. Deep-sea sampling
Dredges and the Agassiz trawl have in the past been the normal
methods of deep-sea collecting, but in recent years some quantitative
work has been attempted.
Expericnce of deep-sea work with quantitative instruments is
limited, but on the Galathea expedition both Petersen and van Veen
grabs were used (Sparck, 1951, 1966). As reported by Thorson (1957a),
however, the van Veen grab was found “ unfit for work a t great ocean
depths as the standing waves or swell at the surface or deeper down
will act upon the levers so as to close the grab long before it hits the
bottom.” How often has a grab been condemned solely because its
release mechanism was faulty !
A grab especially designed for deep-sea work is the Okean grab of
Lisitsin and Udintsev (1965). With its improved release gear, and its
provisions for being lowcred at some speed, it may well become widely
used in the future.
Providing the sampler can be lowered a t a speed fast enough for
coiivenience and without daiiger of tripping the release, almost any
grab could be tricd in deep water. Mr. A. 1 ) . McIntyre informs me that
he has reccntly worked the Aberdeen grab at depths down to 3500 m
in the Indian Ocean. He emphasizt?~ the need to use the thinnest
practicable warp so that it is possible, by watching the accumulator
spring on the lowering davit, to detect when the grab (weighted to
100 kg) touches bottom and again when the strain is taken up to lift
it clear of the bottom.
To sun1 up-there is no instrument which takes really satisfactory
quantitative samples on sandy grounds under open-see conditions.
The choice of sampler will depend upon local conditions, but among
the most widely used are the van Veen and Aberdeen grabs for quantitative sampling ; underwatcr cameras ; and the anchor-dredge for
semi-quantitative work. Although widely used on muddy grounds,
the Petersen grab is not the best choice on a hard sandy bottom.
It is difficult to give a fair estimate of the orange-peel grab’s abilities
on sandy grounds; it appears to be not too satisfactory. I do not
know of any tests comparing the Okean grab with others in common