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Teachers
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Expedition 309
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Journal
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Week 3
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"Back in the Saddle Again" |
23 July 2005 |
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Schematic of the core lab / bridge deck.
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Douglas Wilson, Geophysicist (USA), imaging core on the DMT. *
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A close-up of the DMT Camera. *
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Drilling resumes!
This week I began my quest to observe the processes a core goes through and how each lab works. The work performed in each of the ship’s labs is tied to the work in every other lab. No lab exists on its own because this is a team effort. With all of the nationalities and backgrounds of the science party (I count representatives from six countries in the science party alone), this really is a multi-national effort.
There are four laboratory areas on the bridge deck that adjoin the core splitting and sampling area: physical properties, DMT whole core imaging, core description, and paleomagnetics. As you can see in the diagram, there’s a lot of equipment and very little work space. When there are many people in the core lab during the noon hour shift change, there’s not much elbow room. Fortunately everyone gets along very well.
I began to observe the whole core imaging DMT in operation. The DMT (the name is derived from the initials of the German company that made it, Deutsche Montan Technologie), operated by Douglas Wilson, Geophysicist (USA), and Sara Holter, Undergraduate Trainee (USA), is a digital camera mounted on a track above two rollers. It takes 360° digital images of the whole round core and unrolls it into a flat image. The resulting image can be compared to data obtained from two logging instruments: the Formation Microscanner (FMS) and Ultrasonic Borehole Imager (UBI). The logging will be conducted at the end of the cruise after we finish drilling.
DMT whole core scanning is done so that reorientation of the core pieces, as well as structural identification, planar features, paleomagnetic inclination and true depth of the sample, can be ascertained.
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24 July 2005 |
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In this NASA “GOES Project” image, the band of bright white clouds that cut across the center comprise the Intertropical Convergence Zone (ITCZ).
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Whole round core going through the Multisensor Track (MST) under the watchful eye of Lisa Gilbert, Physical Properties Specialist (USA). *
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There was a core just before shift change at 0530. It went through the system quickly leaving time for me to work on revisions of last week’s journal.
It started out as another rainy day, but cleared up nicely by the afternoon. The JOIDES Resolution is now very near the Intertropical Convergence Zone (ITCZ), where the trade winds of the northern and southern hemispheres meet. The strong sun and warm water of the equator heat the air, increasing its humidity and causing it to rise in the atmosphere. As the air rises it cools, releasing the accumulated moisture. It’s almost always raining in the ITCZ. I started observing and working in the physical properties lab with Lisa Gilbert, Physical Properties Specialist (USA); Masako Tominaga, Physical Properties Specialist (USA); and Trevor Cobine, IODP/TAMU Research Specialist (USA). The primary piece of equipment in use on Expedition 309 is the whole core Multisensor Track (MST). The MST contains four non-contact (they don’t touch the whole round core sample) sensors that measure the following properties:
Magnetic susceptibility: the degree to which a sample can be magnetized
Gamma ray attenuation: wet bulk density using scattering of gamma rays
Natural gamma radiation: amount of discrete decay of the radioactive isotopes of uranium, thorium and potassium
Compressional P-wave velocity: P-wave velocity (not used this trip)
Personnel in the physical properties lab also perform measurements on discrete samples from the core. The properties measured are:
Thermal conductivity: how fast heat moves through a sample
Compressional P-wave velocity: wave propagation through a sample in three directions through contact with the sample
Moisture and density properties: overall density, grain density and porosity from wet and dry samples
The whole round core is passed through the MST, where it is completely scanned. On Expedition 309, the results from the scan appear on the MST computer screen in about 7–10 minutes. If you make a mistake it’s simple – just don’t save the measurements and start over. It’s all automatic, just load and go. It’s like “Star Wars” or “Star Trek.” Too bad this can’t be done in a doctor’s office: no prodding or poking, just a really quick scan!
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25 July 2005 |
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Lisa Gilbert, Physical Properties Specialist (USA), measures P-wave velocity. *
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Today, 2-cm³ samples were chosen by Lisa Gilbert, Physical Properties Specialist (USA); Masako Tominaga, Physical Properties Specialist (USA); Emilio Herrero-Bervera, Paleomagnetist (USA); and Eugenio “Andres” Veloso, Paleomagnetist (Japan), and run through the P-wave velocity device. An oriented cube is inserted in the device, which sends an acoustic signal through the rock. The time that it takes the signal to travel through the rock gives the scientists a velocity measurement. Precise positioning of the sample and tightness of transducers is needed to ensure a good result. The test is repeated in three directions to see if there is a difference in velocity depending on the orientation of the rock.
After the P-wave testing (the velocities of the discrete samples turned out as predicted), the cubes were readied for density tests. The cubes were soaked in seawater in a vacuum for 24 hours, a process that causes the gasses in the pores to be replaced by the sea water.
While preparing for the physical properties tests, and also later, while the tests were running, I took time to work on this week’s journal and part of my final cruise project, a lab that examines density.
We recovered four more cores. By the way, I don’t think I’ve said what kind of rock we’re recovering. It’s predominantly aphyric (lacks crystals that can be seen with the naked eye), slightly altered dark grey basalt (fine grained rock formed from lava) with occasional chilled or glassy margins. After 52 rotating hours, it’s time for another bit change so all the pipe was brought up and the bit was replaced.
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26 July 2005
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Video image of drill string at the mouth of the re-entry cone (Photo by Christopher Smith-Duque, Metamorphic Petrologist (UK)).
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Trevor Cobine, IODP/TAMU Research Specialist (USA), uses the Penta-Pycnometer to measure volume. *
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The new bit was lowered and the hole was re-entered for the fourth time. The re-entry process is still amazing. The camera goes down the drill string, the re-entry cone comes into view, and in a matter of minutes the very long tube of steel is moving down the casing that lines the top of the hole. The TransOcean crew still makes it so look easy.
Back in the physical properties lab, the soaking cubes continue on their path to measure density. The cubes are removed from the sea water and placed on a balance to measure mass. Once this is done they are baked at 100°C to remove the seawater and the dry mass of the cubes is determined. When weighing anything on ship, the movement of the ship causes problems. The high and low measurements (due to the rocking of the ship) during a reading are taken five times and then averaged to get the final mass. Once the mass is established, the cubes are placed in the Penta-Pycnometer to determine volume. This machine replaces the air in the pores of the sample with helium so that a volume can be determined. All values (wet mass, dry mass, volume) are crunched by the computer and a final density for each cube is calculated.
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27 July 2005
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We are now at a total depth of about 4500 meters below the rig floor – that’s approximately 14,812 ft! Over 900 meters (about 2962 ft) is below the sea floor.
As with P-wave velocity testing, results of the density measurements are very close to expectations. The average density of ocean crust is 3.0 g/cm³ and our results were just barely below that. Wow, substantiation!
We retrieved four more cores, making the last one Core 100! One hunderd times rock has been recovered from this site, making the depth of the hole 917 meters (3018 ft) below the sea floor.
Because I’m going to the core description lab next, I read the explanatory notes put together by the nine Expedition 309 core-describing scientists [Carol Cordier, Igneous Petrologist (France); Joerg Geldmacher, Igneous Petrologist (Germany); Sedelia “Sid” Rodriguez Durand, Igneous Petrologist (USA); Takashi Sano, Igneous Petrologist (Japan); Christine Laverne, Metamorphic Petrologist (France); Christopher Smith-Duque, Metamorphic Petrologist (UK); Laura Galli, Metamorphic Petrologist (Italy); Laura Crispini, Structural Geologist (Italy); and Paola Tartarotti, Structural Geologist (Italy)] at the beginning of the cruise. I teach an introductory college level geology class, so the core description lab notes are of great interest. I pulled out my textbook, and started to think about some new teaching strategies for use this fall. It’s great to get a new perspective on the course content every once in a while.
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28 July 2005
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Four more cores came up. Our drilling rate fluctuates depending on the rock type we drill. A major determining factor in drilling rate is the hardness of rock. For example, fine grained rock like basalt slows coring whereas softer brecciated material (angular broken rock fragments held together by a finer grained matrix) may core more quickly. The abundance of fracturing will have a strong effect on recovery. Fractured rock tends to break apart, thereby reducing recovery.
A science meeting was held at 1300. The procedures for requesting samples at the sampling party were discussed. A sample party is a gathering where scientists request samples for later analysis in their shorebased labs by placing coded stickers on the working half of cores. A sample is cut so that it may be taken with them. The final approval of each request is made by the Sample Allocation Committee made up of: Damon Teagle, Co-Chief Scientist (UK); Susumu Umino, Co-Chief Scientist (Japan); Neil Banerjee, IODP/TAMU Staff Scientist/Expedition Project Manager (USA); and Paula Weiss, IODP/TAMU Marine Curatorial Specialist (USA).
Presentations were made by Paola Tartarotti, Structural Geologist (Italy), and Laura Crispini, Structural Geologist (Italy). They discussed their shipboard research and how it relates to what was found on Leg 206, the predecessor cruise to Expedition 309. Their interesting talks gave listeners a glimpse of what the structural geologists are seeing when examining the cores and what direction they are expecting their shipboard research to go.
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29 July 2005 |
While walking on deck today I had a chance to see more of the aquatic and bird life that surrounds us. At least ten mahi-mahi fish were swimming around below where I was standing. They are about 2 to 3 feet long, flat-nosed, and are a brilliant fluorescent blue and green. They show up really well in the dark blue water. It’s overcast, so the water is even darker than it would be under sunny skies. On the bird side of life, the number of brown boobies has increased. Each time you look up at the derrick, there are more and more of them. Occasionally there are a few seagulls present. If the number of birds keeps increasing, it’s going to look like a scene from the Alfred Hitchcock thriller, “The Birds.”
Once a week we have a shipboard safety drill and today is no exception – it’s the lifeboat drill. At 1300 the lifeboat drill alarm is sounded and we reported to our assigned lifeboats. Ah, the eccentricities of shipboard life!
At a science meeting after the drill, we were able to hear a brief summary from each of the groups on their progress so far. I’ll repeat myself - the knowledge in that room is staggering.
It was amazing to see what’s been accomplished so far, and their plans for the rest of this cruise. There are even some who are planning their return to Hole 1256D in October-December 2005 on Expedition 312.
Tonight is “Chick Flick Friday” (so named by the women sailing on this expedition), also known as “Ladies Night Out.” I’m told Monday will be reserved for “Guy’s Movie Night.”
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Next Installment: “And the ‘Bit’ Goes On”
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* Photo by Shannon Housley, Imaging Specialist, IODP/TAMU (USA) |
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