Method
A heavy metal 4-inch-diameter pipe or a metal box of comparable size is attached to a strong cable. Several hundred pounds of weights are attached to overcome buoyancy. The assemblage is dropped overboard and forced onto the ocean floor to collect the core sample. A door in the bottom of the sampling device closes so the sediment stays inside the pipe or box. The device containing the sample is then raised and recovered by the vessel. When done expertly, the sediment sample retains the original sea bottom stratification necessary for accurate analysis.
Climate Change
Specific analytical techniques are used for each research area. For example, climate change research may compare the thicknesses of different sediment strata taken from one area to that retrieved in a related region. Variations in their shape and thickness indicate changes in ocean currents over several thousand years. Micropaleontologists may study core samples to determine plankton evolution that took place over several millennia, indicators of changes in sea temperature. Samples are archived for use as benchmarks for future sample comparison.
Seismology
Seismologists take core samples from the ocean floor near large subduction faults on the ocean floor. Each of these faults is the location of one huge tectonic plate riding over another. Some of the samples are archived for future reference. Others are analyzed as quickly as possible because specific sediment qualities change when exposed to air or lower-than-normal atmospheric pressure. Layers of ash near the subduction faults provide valuable data about past volcanic eruptions associated with earthquakes.
Paleooceangraphy
Paleooceangraphers study the fossil remains of ancient ocean life for clues about changes in population levels and what may have caused them. The presence of specific seashells in the right amounts indicates one set of environmental conditions, while the sodium, magnesium and calcium levels in another sediment stratum may indicate something quite different to researchers.
Industrial Use
Using many of the same methods used by scientific expeditions, petroleum explorers take core samples from the ocean floors in locations likely to contain oil deposits. The presence of salt domes and certain microfossils under the sea bottom are primary indicators of petroleum. Very often these petroleum expeditions work in concert with scientific programs by sharing core samples and data.
Corer Types
Within the two general classes of pipe and box corers, there are variants designed to handle a particular sample. The NOCS long piston corer was designed to retrieve deeper cores and is capable of drilling nearly 40 feet into the ocean floor. A box corer is used for collecting smaller samples and reaches a depth of about 40 inches.