7 weeks 6 days
The Core Saga Continues…
Submitted by Dena Rosenberger on Sat, 11/10/2012 - 22:24
Where are we now?
Off the western coast of Costa Rica, in the Pacific Ocean. Our coordinates are still N 8°36 min, W 84°4 min as we continue coring operations at this site. Water a bit choppy today, but not much swell. Water temperature is 27 °C and air temperature went up a bit to 29.5 °C (that's about 85 °F), and the water depth is about 500 meters. The red tag marked "A" is us!
Sunset was spectacular, as usual...
Scientists at Work
Cores continued to appear regularly through the night and today, and the sample table was very busy. Many people work in 12-hour shifts at the sample table whenever cores are coming in to collect all of the samples that each scientist has requested. This half of the core is called the “working half.” Since I have other duties, I only work a 2-hour shift at the table. Here, Yuzuru Yamamoto and Debora Nascimento work at the table to collect samples.
All metal jewelry must be removed before you can work with the core so that no metal atoms contaminate the samples and give a false reading. They also use a knife made of ceramic to cut samples out, again so that no metals contaminate the core. It doesn’t really look sharp, but it is! So, they remind you by sticking it in a labeled Styrofoam chunk.
The first step is to check the spreadsheet to see what kind and how many samples each scientist wants. For example, a scientist may want a 10 cubic centimeter (cc) sample every 25 centimeters for each 1.5 meter core section. Then a tag with that scientist’s name is placed along the core everywhere they requested a sample be taken. After all of the request tags have been placed, samples start to be removed from the half core, placed in small containers, then in bags, sealed, and placed in a box with that scientist’s name.
A small piece of Styrofoam is cut and placed in the hole so that the core retains its shape and also so that we can see that a sample has been removed at that spot.
Mari Hamahashi uses a tool that measures “Compressive Strength” that helps to determine the hardness of the core sample at various places. This is the maximum force in pounds per square inch (psi) that can be applied to a rock sample without breaking it. This device doesn’t take anything from the core, but just pushes a small amount of air against it and measures its resistance.
Scientists continue to look for fossils and other indicators in these cores that are dominated by massive dark-greenish gray clayey siltstone. Also, they are finding bioturbated carbon-rich areas in the core. “Bioturbated” means either that some organism, like a worm, crawled around in the sediment before it became a rock and messed up the soil. Plants can also cause an area to be bioturbated with their roots.
As of last night, the coring was completed down to about 700 mbsf (meters below sea floor), and the target depth is 800 mbsf. Due to the condition of the core at that depth, they had switched to pulling up half cores to maximize core recovery. If everything goes as planned, they should be pulling up the last core early tomorrow morning and will then start logging. Logging is lowering devices into the borehole that measure various parameters. The first device is called…the Triple Combo Ultrasonic Borehole Imager, or TC UBI, which measures hole diameter, natural gamma radiation, density, electrical resistance, and takes ultrasound images.
Life on Board
In the main stairwell, they have made one corner the “Pet Stop” where people put up pictures of the special pets that they miss at home. Awww…
We had our second fire drill today (photo courtesy of John Beck)
And this time, we got to go inside the lifeboats. The instructor at my station was John Powell, the Second Mate on the JR. In theory, these boats can hold up to 70 people each (we have about 125 people on board), and there are four boats. It would be REALLY crowded in there with 70 people. And no windows.
Each boat contains some food and water, and signaling devices to that send out your coordinates. Even though we did not get to be lowered into the water, he showed us how to actually drive the thing in case of emergency.
It would not be a fun place to be for very long, especially if the ocean was rough.
From the subduction zone, in the wide Pacific…