Transcript for Oceanfloor Legacy, segment 10 of 14


The first sediment cores are taken in the apparently smooth, gently sloping region that stood out on the large mosaic.

And a gravity core is a very simple instrument that consists of a weight stand that weighs - either we can set it to weigh either eight hundred pounds or two thousand pounds, and attached to the weight stand is a long barrel. This barrel's three meters, or ten feet in length, and inside the barrel we put a plastic liner, and then the bottom of the barrel is capped off with what we call a core catcher, and this is just a cap that has a set of springs, of fingerlike springs inside so when the barrel is lowered from the ship and then it free-falls to the bottom, and it's the weight of the stand that drives this pipe into the bottom, and the sediment goes up inside the liner, and the steel spring fingers, as the sediment goes up, open up, and then as you pull the barrel back up off the bottom, the fingers close, and the sediment can't get out of the core.

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Gravity cores are taken throughout the research area except in the vicinity of the radioactive waste dump sites. It is uncertain exactly where the drums were dumped so the radiation specialist tests each core for radioactivity throughout the sampling process. As a precaution, the deck crew wear rain slickers and gloves to protect them against potentially contaminated splattering mud. Fortunately, none of the thirty cores shows radiation levels above what is considered normal. The scientists will use the cores to create a model describing the movement of sediment and bottom currents in the research area. This information will be critical in determining areas where dredged material can best be contained on the sea floor.

Processing of the cores involves breaking them down to more manageable lengths for analysis in the shipboard lab.

When you collect the core, you try to use it as many ways as possible to give you different clues on what's going on on the sea floor. One of the principal tasks we can do is see what type of sediment's there, and anybody who lives in California knows certain types are susceptible to landslides. This is an earthquake area, and from simply onboard ship we're going to run some very simple engineering tests on split cores to more sophisticated tests in the laboratory at home to see what their susceptibility to landsliding under earthquake loading is, under earthquake shaking, and obviously before we get to that stage, we have to see if they're stable just the way they're sitting now. If you dump something on them, will that initiate them to slide?

In addition to stable areas, they attempt to locate sites with minimal current activity where disposed dredged material would be least likely to wash away. By splitting the cores lengthwise the scientists get a clear view of the sediment section and a clean surface to sample from. Each section of split core represents several thousand years of sediment accumulation, providing an important historical record of past sea floor activity. The dark patches here are burrows dug by clams or worms that once lived just below the sea floor surface.

The split sections are slid into storage cases called D tubes which will be kept in a refrigerated core library at the U. S. G. S. branch of Pacific marine geology in the San Francisco Bay area.

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