Grab sampler

　Grab sampler is a generic name for a type of sampler that uses a semicircular bucket (grab bucket), which opens from side to side, to grab and collect sediments on the seafloor like a crane game. Although the sample is disturbed during collection, it is a simple method to investigate the nature of the sediment surface layer and the composition of components in the sediment. It is also used to collect benthic organisms living in the sediment and on the seafloor surface. Typical grab-type mud samplers include the Okean grab sampler, Smith McIntyre sampler, and Ekman barge sampler.

・Okean grab sampler

　The Okean grab sampler is a grab-type mud sampler that combines a grab bucket and a balance trigger. When the grabbing device approaches the seabed, the balance trigger operates, causing the grabbing device to free-fall. The momentum of the fall causes the grab bucket to dip into the seabed. The weight of the grab bucket is so great that it can collect samples even from relatively hard bottom sediments such as sand and gravel. When the wire is wound up, the grab bucket grabs the sediment and closes the top cover of the grab bucket in conjunction with it. The top cover keeps the sample in the bucket from being lost in the sea when the grab bucket is retrieved. If the bottom sediment is too soft, the grab bucket will be buried in the seabed and the mud sampler will not be able to collect samples from the sediment surface.

       Fig 7 Okean grab sampler

・Smith McIntyre Grab sampler

　The Smith McIntyre Grab sampler is a grab-type sampler that combines a grab bucket and a device that closes the bucket using the force of a spring in a metal frame. The main body of the grab bucket is dropped freely from near the seafloor, and the mud sampler is allowed to sink to the seafloor. Usually, the grab bucket is buried to the part of the grab bucket, and at the same time, a trigger attached to the frame operates to close the grab bucket and its top cover. This mud collector is lighter than the Okean grab sampler because the thickness of the grab bucket is thinner. If the bottom sediment is relatively hard, additional weights can be attached to the frame to increase its own weight for observation. It is often used for biological surveys in shallow water areas because it is easy to handle and can gouge out a fixed area of the seafloor.

　 Fig 9　Smith McIntyre Grab sampler

 Picture provided by：Tottori Prefectural Fisheries Experiment Station.　（https://www.pref.tottori.lg.jp/item/838972.htm）

・Ekman barge sampler

　This is a grab-type mud sampler with a grab bucket attached to the bottom of a cubic box that is closed using the restorative force of a spring. First, the grabbler is lowered to the seafloor and allowed to land on the bottom. Then, when the messenger is dropped and the trigger is activated, the grab bucket closes and the sediment is collected. This is the simplest and smallest of the grab type mud samplers and is suitable for simple surveys in lakes, bays, and coastal areas.

　　　図１１　Ekman barge sampler