Getting to the Crux of Coring (Part 3 of 3)

Earth Observatory Blog

Getting to the Crux of Coring (Part 3 of 3)

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Once the pipe is inserted into the bottom of the piston, it will be held in place by a security jaw.

Obviously, no one on deck gets to see this momentous event since it’s happening 4.5 km below sea level, but the pipe’s collision with the seafloor can be followed on a monitor that tracks the tension of the polymer cable. As the coring unit makes its three-to-four hour descent, the tension on the cable is about 6.5 tons — it drops to zero when the pipe hits the seafloor, then spikes to about 11 tons as it’s pulled from the sticky mud. On the way back up, which takes another three-to-four hours, the tension is greater than it was on the way down, thanks to the weight of the mud now trapped inside the pipe.

The trigger arm itself is attached to the top of the piston at the last minute, just before a specially designed winch lowers the entire coring unit into the sea.

What you can see on deck, though, is the process of assembling the coring machinery, as well as how the crew lowers the whole thing into the water and pulls it out again. I was especially intrigued by the ways in which rope and cable are used to solve tricky problems. For example, the rope that’s attached to the trigger-arm weight has a splice in it, which makes it easier to transfer from the winch that lowers it into the ocean to the trigger arm itself.

Upon its return to the surface, crew members inspect the hardware to make sure everything is intact, and ready themselves for the next steps — securing the piston to the fork and then separating the piston from the pipe.

Even more impressive are the cables that are looped around the vertical coring pipe to bring it to a horizontal position on deck. The first cable is the longest, dropped close to the pipe’s impact end, the second is shorter, and so on. Thanks to these different lengths of cable, multiple winch operators along the starboard side of the Marion Dufresne can work as a team to slowly raise the pipe to a horizontal position. The solution is simplicity itself, even though the operation takes planning and experience to execute. But that’s what the crew of the Marion Dufresne and the IPEV team do every day — they routinely make difficult and complicated tasks look easy.

Mr Yvan Reaud cannot help but lend a hand as the coring unit returns from its trip to the bottom of the sea.

Click here for Part 1 and here for Part 2.

To continue to follow the progress of MIRAGE, please check the EOS blog throughout the month of July, and spread the word using #MIRAGEcruise.

All photographs are taken by Ben Marks, unless otherwise stated.

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