11 February, 2001
-66.29 lat 147.40 long
The Jumbo Piston Core (JPC) and the Kasten Core
There are two kinds of coring device: a Kasten core and a jumbo piston core. The Kasten core is like a metal box with several hundred pounds of weight on top. They deploy the Kasten core with a winch and wire off the back of the ship Once deployed we watch the monitor to see when the core reaches the ocean floor by the decrease in wire tension, displayed on the screen. We then stop the winch and pull the core gently back out of the sediment, and back up to the sea surface. The Kasten core is important for sampling where the ocean floor meets the water. It is this "sediment water interface" that tells us we have recovered the very top most surface of the sediment. Often times this is lost when we use the jumbo piston core (described next). Once the Kasten core is back on board, we make a decision whether to deploy the jumbo piston core. It is quite an operation; the piston core is an 80 foot steel pipe around an equal amount of plastic PVC pipe. The PVC pipe, or liner, is just regular plastic four inch drainpipe. The liner is cut into eight ten-foot sections, joined together end to end inside the steel pipe. The core is deployed over the side of the ship by winch and wire. As it approaches the sea floor, a lever arm attached to the side of the piston core with a small weight on it hits the bottom first, releasing a catch so that the jumbo piston core free-falls and hits the bottom. With up to 4500 pounds of weight behind it, the jumbo piston core hopefully sinks 80 feet down into the sediment. Suction pulls the sediment up into the liner as the core pushes through it. Why do we need suction* ? On the bottom of the piston core is a core catcher, which stops the sediment from falling out as the core is withdrawn from the floor. Once the core is at the sea surface again, we use a crane to put it on the side of the deck railing. Then a hydraulic motor pushes the liners out ten feet at a time. A "cap" is put on the ends of each section, with labeling to indicate core top , bottom, and station number. The individual core sections are then carried into the lab for processing (processing next week). Lots of things have to work right, and lots of things can go wrong (entries to follow). It is a very tense and nerve wracking procedure, but so far we have had three successful cores up and on board.
*so the sediment will go up into the tube
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