Gravity Drop and Piston Coring

Brief description

Image courtesy of Fugro
Gravity corers provide a rapid means of obtaining a continuous core sample in water depths down to several thousand metres. Depending upon their deployment and operating systems, gravity corers can be deployed from a wide range of vessels. A gravity corer consists of a steel tube in which is inserted a plastic liner to retain the core sample. The penetrating end of the tube is fitted with a cutter and a concave spring-steel core-catcher to retain the sample when the corer is retracted from the soil and recovered to the ship. One of the simplest geotechnical devices, the impetus of gravity acting on the heavy, freefalling device is the motive force that drives the corer into the soil.

Drop coring is similar to vibrocoring, see NOAA's summary table at summary view of sediment vibrocoring technique (144 KB PDF).



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Gravity Drop and Piston Coring of Seabed Sediments

Sediment cores of the seabed are obtained by means of a hollow tube or box which is driven into the sediment by means of gravity or a reactionary force and taken up to obtain a continuous, undisturbed cross-section core of the seabed. The core is extruded or cut open for analysis by means of subsampling the chemical, biological, and physical properties of the ground. The sediment cores provide information about the composition of the sediment column such as what is living in the sediments, sedimentation rates, magnetic properties, total organic carbon, grain size sampling, trace metal concentrations, and organic pollutants. A coring program is an important way to ground truth the remote sensing done in acoustic and video surveys. In the case studies the seabed cores were obtained by means of a vibrocorer manufactured and supplied by Quaternary Resources. The vibrocorer can achieve better results than a drop corer in most sedimentary conditions. The cores are very similar and are used in conjunction with side-scan sonar, sub-bottom profilers, multibeam bathymetry, and grab sampling to map benthic habitats.

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