Sediment grabs come in all shapes and sizes, but they all do much the same thing, to collect a sample of sediment from the seabed. These samples are used to analyse the properties of the sediment itself or to discover the marine life living on the seafloor.
Sediment grabs are often named after their inventors. For example, the Smith-MacIntyre grab is lowered from ships, and on contact with the seabed, a split cylindrical bucket is triggered which scoops up about 10 litres of sediment. Another is the Van-Veen grab, like a giant pair of tongs which closes two halves of the bucket together as the winch draws the cable in. Sediment is then evenly scooped into the large buckets. A box core uses trigger plates that contact the seafloor to close the top and bottom of a metal box plunged into the seabed. This device neatly extracts a plug of sediment that is mostly undisturbed and allows scientists to examine the layers of sediment carefully and any marine life found within.
Sediment samples can tell scientists a lot about the ocean above the seabed because of the particles that drift down through the water column to the seafloor, and also about the geology that lies beneath the seabed surface. For example, sediment samples can be used to measure the grain size, limestone or silica content, trace element and nutrient levels. These are basic measurements of the seabed which are just as important as if describing the characteristics of soils on land.
As well, much of our knowledge about the animals that live in and on the seabed have come through looking at the rocks and mud collected by sediment grabs. Worms and other sediment-feeding animals make their homes in the seabed and a grab is often the most simple device used to collect them.
The Gallery images and Movie below are examples from various sediment grabs conducted on the Great Barrier Reef, Coral Sea and in Antarctica.