Simple clam shell type bottom grabs have been used effectively for many decades to sample the top few centimeters of soft sediments. A very common sampler is the Van Veen grab. If a sediment is very flocculant, this sampler will "blow away" some of the surficial material, perhaps losing important information. Grabs also tend to mix the sample, providing a mixed 0-5 cm. surface sample. Because of its simplicity of operation and low cost, grab samples remain an important sediment sampling device.
Corers of numerous types have been developed and used during the past 2-3 decades of coastal ocean research. Small gravity corers are simply a core tube with a weight attached. Simple to use, these plunge through the water column and penetrate by striking the bottom with velocity. A reasonable short core can be taken easily, but the sediment-water interface is likely to be compromised. Box corers of several designs can be used to take a more precisely located core sample that can be sectioned with depth to provide a record of sedimentation and the processes controlling the deposition rate and mixing. Simple physical compression of the sediment occurs when any sampling device penetrates the mud and any sample that will be sectioned by depth must use an independent measure to relate position in the corer with depth in nature. To take a sample at the sediment-water interface, some method to control the penetration is required. Penetration control may be mechanical as with the MK-III Box Corer or hydraulic, as with the Hydraulically Damped Corer. Each of these corers takes a good sample; the hydraulically damped corer captures an overlying water sample more securely but the MK-III takes a much larger sample for those who need more sample material.
One of the simplest and most commonly used sediment corers.
The epibenthic sled is designed to trawl just above the bottom at the sediment water interface (the epibenthic zone).
This sediment sampler has a clam shell-type scoop setup.
The gravity corer allows researchers to sample and study sediment layers at the bottom of lakes or oceans. It got its name because gravity carries it to the bottom of the water body.
Source: Ocean Instruments
This instrument, like other corers and grab samplers, is used to sample sediments from the ocean floor.