Story: Sea floor geology
Page 8 – Exploring the sea bed
The type of equipment used by New Zealand scientists to sample marine sediment depends on the needs of the survey and the nature of the seabed. Dredges are used to collect rock and gravel, while corers and grabs recover sand and mud. These devices are normally operated from ships, such as the Tangaroa, owned by the National Institute for Water and Atmospheric research. In very shallow waters, divers can collect samples with hand-held corers.
Dredges and grabs
Dredges are large metal buckets and cages that are dragged by a steel wire across rough, hard areas of the sea floor. They are used on fields of manganese nodules and underwater volcanoes.
Grabs have jaws that close when they hit the sea floor, and are useful for recovering muddy material.
Corers and drills
Corers are used to extract a core – a cylindrical sample of sediment. Corers consist of a square or round barrel up to 50 metres long. A heavy weight rests on the barrel, pushing it into the sediment. These are known as gravity corers. Some have a piston inside the barrel to create a vacuum that assists entry into the seabed. This technique enables longer cores than those collected by simple gravity. Some corers have a door that snaps shut to hold in the sediment while the barrel is withdrawn from the seabed.
Hydraulic drilling techniques are used in the deep ocean to obtain very long core samples. Submersibles and remotely operated vehicles are also used.
The seabed, and the plants and animals that live there, can be filmed from survey vessels. Instruments known as benthic landers or tripods can be placed on the sea floor and remotely operated by computers, to make long-term observations.