Van Veen grab sampler
The Van Veen Grab Sampler is limnological instrument to sample sediment in the ocean. Usually it is a clamshell bucket made out of stainless steel. Up to 20 cm deep samples of roughly 0.1 m2 can be extracted with this instrument. It is light-weight (roughly 5 kg) and low-tech. The smallest version even fits into hand luggage.
A draw-back of the use of this sampler is that it tends to disturb the sediments more than a box corer does. The Van Veen Grab it is not designed to sample living organisms.
Mechanism
While letting the instrument down into the water, the two levers with buckets at their ends are spread like an open scissor. The levers are locked in this position, and unlock when hitting the ground. When the rope is pulled upward again, the two buckets close and grab a sample from the sea floor.
Two Small technical changes lead to variations with more mechanical parts:
- The Ekman Grab Sampler does not close the shovels instantly on ground contact, but a messenger weight has to be sent down in order to release springs and take the sample.
- The Ponar Type Sampler is modified also has additional springs which are released upon bottom contact which might be helpful for harder surfaces.