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Piston Coring

Today piston coring is one of the more common sea floor sampling methods. The piston corer was invented in 1947 by Professor Borje Kullenberg to enable the Swedish Deep Sea Expedition to collect long samples of sediment, up to 24 meters long, from beneath the sea floor. This tool acquires samples that are virtually undisturbed, making this tool and modified versions of it a staple in modern sea floor sampling.

Let's take look at the tool and its core sample, and see how it all works.

Piston Corer
(Photo used by permission, Dr. Mark L. Holmes, Univ. of Washington).

The piston coring tool is winched over the side of the research ship just prior to a sampling run. Notice the long coring tube where the sea floor sediment will be collected, the weight located on top of the tube and the trip arm extending to the left above the weight.

Modified Kullenberg piston corer.
(Credit: US Coast Guard)

Panel 1 - The piston corer appears much as it did in the previous photo, but it is now approaching the sea floor. Notice the parts of the tool, the piston corer, the piston at the tip, and the weight, tripping arm, loops of trawl wire and gravity corer. The entire assembly is connected by wire to the winch on the ship.

Panel 2 - The gravity corer has just touched the sea floor. This triggers the release of the piston corer and it drops to the seafloor. The weight helps the corer impact the sea floor.

Panel 3 - The trawl wire is fully extended stopping the piston inside the core tube, however the core tube continues to penetrate the sea bottom. The vacuum suction created by the stopped piston and moving tube allows the sediment sample to enter the tube comparatively undisturbed. As soon as the sample is inside the core tube, the entire assembly is winched back on board the ship.

Piston core removed from corer.
(Credit: U.S. Geological Survey, US Department of the Interior Eddy Lee,
Texas A&M University, aboard the R/V Gyre)

Once the assembly is back on board, the piston core sample is removed from the corer and cut into more manageable lengths. These small core segments are later cut in half lengthwise so the sample can be examined and subsampled.

Split piston core being subsampled.
(Credit: U.S. Geological Survey, US Department of the Interior Hans Nelson
and Gita Dunhill, USGS - Menlo Park, aboard the R/V Gyre)

The cut and split core sections are described and subsampled for detailed analysis that often includes foram age and environment analysis.

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References

Oceanography (undated) Goteborg University Earth Sciences Center website http://www.oce.gu.se/about.html accessed on October 14, 2004.

Revised on: January 2, 2005