Thursday, June 9, 2016

More cores are collected and processed

The official CASEIS Cruise Blog is located here: This official blog is written by my shift-mate Lola Johannes.

We continue to collect sedimentary cores...

    June 6, 2016

  • Here is a site map for the cores that we have collected so far. This is similar to maps that I have previously posted. The planned sites are in green, yellow, and red that are ranked by color from high to low priority. The dots in blue show the locations of our actual core sites.
  • This is the Multi Sensor Track (MST), also known as the Multi Core Sensing Logger (MSCL) manufactured by GeoTek. In prior posts I show how this device is used to scan real color imagery (RGB) of the split cores. Here the MST is configured to collect four principle geophysical properties of the cores. These properties are the first that are measured after the core is cut up into 1.5 m segments and labeled. From right to left, the properties include: Gamma Density, P-Wave Velocity, Resistivity, and Loop Magnetic Susceptibility. Below is a general description of each of these measurements.
    1. Gamma Density Here, there is a source of gamma radiation, 137Cs located in a canister with yellow stickers. The stickers warn the user of the source of radiation. The gamma rays are emitted away from the operator of the instrument. As they pass through the core, they are absorbed differently by materials with different density. The sensor (out of view on the far side of the track) measures the amount of radiation that makes it through the core. This is, in essence, a way of measuring the density of the material in the core.
    2. P-Wave Velocity The blue parts of this instrument send seismic P-Waves through the core. The P-Wave velocity will vary depending upon the density, bulk modulus, and shear modulus of the material in the sediment core. The bulk and shear moduli are two measures of elastic properties of materials.
    3. Resistivity There is a source and sensor on the bottom of the track that measures the conductivity of the materials in the sediment core. These data are integrated over a large portion of the core and are generally of little use for us. The data typically have a long wavelength signal and we are interested in short wavelength signals (like found in mag sus and density data).
    4. Loop Magnetic Susceptibility As the core is passed through the white plastic device, it passes through a wire that applies a magnetic field through the core. Mag Sus is essentially a measure of how well the sediment can hold a magnetic charge. In other words, how much of the material in the sediment core is composed of magnetic minerals, like magnetite. Because these magnetic minerals tend to be more dense, the mag sus data generally covary (i.e. match) the density data. There are some cases when these data do not covary, like in tephras. Tephras will have high mag sus values, but low density values (in general).
  • Here Quentin D. is collecting a U-Channel sample from the work half of this sediment core section. Some of the sediment is very stiff and difficult to insert the u-channel into. So, we place the u-channel on the sediment to make marks. Then we use a knife or a putty knife to cut into the sediment, making it easier to insert the u-channel. In the second photo Quentin is being dramatic for the photo because an important aspect of all life on Earth is to have a little fun.
  • Here Marie is looking at a small sample of the sediment that has been placed in water to check for microfossil content. Microfossils can tell us the oceanographic conditions in place when the sediment was deposited. In some cases, these are the conditions at place on the seafloor where the sediment is found. In other cases, the sediment is transported and reworked (so the microfossils tell us something about from where the sediment came from before it was deposited in the core location.
  • Once the cores have been described and measured for geophysical properties, we place them in plastic bags and then these plastic boxes. We can see that we are being quite successful in filling this refrigerated area of the ship. This area will be completely full by the end of the cruise (fingers crossed).
  • Here Dr. Beck and I are splitting the core section in half. First we cut the core with a special saw and then we run a wire through this cut. In some cases, the sediment is too stiff to run the wire, so we need to place a putty knife through the core partway to make it easier to slice the sediment with the wire. Anyone familiar with cutting clay for making ceramic vases, plates, etc. would be familiar with this method.
  • Here is the core that we just split. This is core CAS16-09PC section I (the top). The top of the core is on the near side and the base of this core section is on the far side (out of focus). The section on the left is labeled W and is the work half (the half that gets described and sampled with the u-channel) and the half on the right is labeled A for being the archive half (the half that gets imaged and measured for point mag sus, photospectrometry, and possibly X-Ray Fluorescence). There is a gap in the sediment that is where a large magnet was removed. The magnet is a component of the coring operation.
  • Here Dr. St-Onge has completed taking the u-channel and is filling the empty space with foam so the core section can be packaged into the rectangular boxes for shipment to the core repository. His graduate students will be conducting paleomagnetic measurements on these u-channels, so he is very excited to ensure that these u-channel samples are collected, prepared, and stored properly. This meticulous work is necessary to ensure that the sediment is not disturbed.
  • Here Rachel Haussman, an undergraduate student of Dr. Chris Goldfinger’s (who will join the cruise on the second leg). Ms. Haussman is labeling the rectangular boxes and the blue end caps. We call these D-tubes because the original plastic boxes were not rectangular, but shaped like a D (like the cross section of a core section half). Ms. Haussman is making sure to label all these parts carefully so that it is easy to quickly tell what core section is in the box.
  • June 7, 2016

  • Here we review safety protocols that we take during our work shift. While working on a ship, it is very important that we are careful not to injure ourselves. If we are injured, we are far away from hospital care if that is needed. There is medical care aboard the ship, but there are limitations as far as how extensive the care that might be needed. For example, there is not a surgeon on board. So, if a crew member needs this specialized care, they would either need to be evacuated by helicopter or the ship would need to return to port. To prevent this, we have strict safety protocols that we follow. Recently a crew member had a medical condition that required a helicopter evacuation. See the official blog linked above for photos of the helicopter evacuation.
  • The ship’s crew has prepared this core for our longest core (yet) for this cruise. The core length is 29 meters. We hope to sample a long paleoseismic record in this core. This core is CAS16-12PC (see map above for the blue dot labeled 12). The core actually got plugged by a stiff clay layer, so “rodded” which prevented any more sediment from entering the core. The actual core length was only 18.53 m.
  • Here Dr. Beck, Quentin D., and I take a look at a map showing the multibeam bathymetry (dark blue = deeper; light green = shallower) that we have collected during this cruise. We use these bathymetry data to help locate core sites and to plan for CHIRP seismic data acquisition (which is also necessary for site planning).
  • Dr. Feuillet awaits the arrival of core 12PC. The core has been rotated from vertical to horizontal and now hangs from winches. These winches will then move the core on board and lower the core into rollers so the liner can be removed.
  • Here Patrice (the coring engineer on the left) explains some of his analysis from the coring of this core 12PC. He is presenting his results to Dr. Feuillet and the Captain (in the red helmet). Patrice and his coring team have sophisticated ways of knowing how far the core penetrates into the sea floor and many other parameters. Patrice and his team are possibly the most advanced corers on the seas today. I am lucky to be able to work with these scientists and engineers.
  • This is a box corer. This device samples the seafloor with a square tube about 50 cm on each side. There is a scoop (on the right) that, after the corer is embedded into the sediment, scoops down to cover the bottom of the corer to collect the sediment into the box. Check out the official blog site for a photo of the box corer full of sediment.
  • June 8, 2016

  • Quentin D. is busy describing this sediment core section. However, he takes a brief moment to pose for an imaginary magazine photo shoot for the cover of a magazine entitled “Marine Geology Quarterly” (an imaginary gentleman’s magazine)
  • Here Chloe is cleaning the u-channel of excess sediment. This is important because this excess sediment is deformed, so will give incorrect paleomagnetic measurements.
  • Here Lola is also carefully cleaning the u-channel for CAS16-12PC section XI.
  • Chloe is labeling the u-channel lid. We label everything!

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