Wednesday, June 1, 2016

Cores 3 and 4 have been acquired, marking our longest core so far!

The official CASEIS Cruise Blog is located here: http://www.ipgp.fr/caseis This official blog is written by my shift-mate Lola Johannes.

We collected our 3rd core today and are now collecting the 4th.

  • We collected our third core today in a sedimentary basin to the East of Guadeloupe. This basin appears to be isolated from terrigenous sedimentary input. The seafloor is again very deep at ~5800 m. So, it was surprising that we saw abundant forams in the mud that coated the core barrel when it came up on the ship. We extended our core barrel to 14 m, but only received 9.44 m of sediment. This core is the blue dot labled "3" in the map below. Our next core location is near the yellow dot between core sites 1 and 2.
  • Here Quentin D. awaits core CAS16-03PC. We watch the core be rotated from vertical to horizontal so that it can be brought up onto the ship. Then the core liner will be removed.
  • Here Patrice (the coring engineer who controls the settings on the piston corer) takes a look at the sediment in the core tip. We are all interested in this sediment as it helps us learn about why the core may or may not penetrate into the seafloor. Our initial core got stuck in some sandy sediment (we think?), and we have identified this sediment in the seismic records. At this core site, this same layer appeared to be slightly different, suggesting that we might be able to core into it. Unfortunately we did not core into this layer, so we were unable to test our hypothesis. We will have the opportunity to test this hypothesis again with the next core.
  • The seismic data show that each basin, which generally have isolated sources of sediment, have very similar seismic records. The differences between these coring sites, it appears, is that some basins have expanded section (the same layers are thicker, or “expanded”). Other basins have the same layers, but are thinner.
  • For paleoseismic investigations, we are very interested in expanded section because the layers have the most amount of information. When the layers of sediment are thinner, this information is stuffed into a smaller space, making it more difficult to tell the layers apart. Being able to correlate sedimentary layers from cores in different basins is the key tool for being able to interpret these layers to have been caused by earthquakes.
  • Here is a view of the core tip, showing the clay rich sediment. We watch the core as it arrives above the water surface to see if it has sediment coated on it. Sometimes the entire core can be submerged in the sediment, so the rectangular part of the coring device (the weight stand) can be coated in sediment too. This would be bad news as it would suggest that the corer went too deep into the sediment and that we might not have cored the top of the seafloor. There was a M 8.5 earthquake on 8 Feb. 1843 (mentioned in a previous post here. If sedimentary evidence of this earthquake is to be found in any of these cores, it will be in the uppermost decimeters of sediment. So, it is very important that we sample the seafloor.
  • Here the engineers remove the core tip and core catcher (basically a one-way flap that prevents sediment that has been collected in the core barrel stays in the core barrel), both which can contain sediment that we collect for later analyses.
  • In this case, there is still sediment in the tip of the core barrel, so the engineer removes some of this so that they can connect a device that grabs the core liner so that we can pull the liner out of the core barrel.
  • Here we have pulled the core liner out of the barrel and placed the liner on stations so that we can label and cut it into 150 cm sections or shorter. Quentin #2 and Dr. Nathalie Feuillet await in anticipation to see how much sediment is in the core liner.
  • Here the engineers prepare the core barrel to be used again. This time, they are configuring the core to be 22.4 meters long. First they are screwing another core barrel on, then they will glue two liners together and place that in the core barrel, with the core tip and core catcher on last. We will be coring in a basin that has an expanded section (each sedimentary layer is thicker than in other basins. For example, a layer base than might be 10 meters deep in one basin might be 20 meters deep in a basin with expanded section.
  • Here Lola is labeling the end caps for the core section. Each core section gets an end cap that contains all the information about that core section. We choose to label every part that is associated with a core section. That way, if someone makes a mistake, it is easier to correct it. It is very important that we keep track of every gram of sediment that we collect. This type of research is very expensive, so we make sure that we are accountable. This is also important from the scientific view, because we want to keep track of our data sources with the greatest diligence.
  • Here is a map showing our cruise trackline (the record of where the ship went). The tracklinne is the black line and the current ship's location is the black symbol (circle with two arrows) at the end of the black line. The planned trackline is an orange line and due to water and wind currents, the actual trackline is slightly different. This shows how we cross a core site in two direction to collect seismic reflection data. This allows us to know the sediment stratigraphic relations for the core site. This also allows us to change our core site if we can see a location that has better stratigraphy in some way.
  • Here I am with my lab coat on. I am using a stethoscope to find out what is in these sediment cores (core CAS16-03PC). I think that this is not working well and that maybe the traditional approach is better. My colleagues agree, so we will abandon this attempt to discover what is inside these cores.
  • Here Dr. Feuillet is awaiting the arrival of our 22.4 meter core, CAS16-04PC. She is observing that there is sediment on the outside of the core barrel. This means that the core has been embedded in sediment on the seafloor (i.e. that the core did not fall on its side when it hit the seafloor). We always like to get some of this sediment on our finger as soon as we can so that we can get some idea about what is at the seafloor. We are always looking for foraminifera fossils because they can be used for radiocarbon age control. After we get the core on deck and determine the amount of sediment in it, we find that there is about 19 meters of sediment! This is great news!!! We surpassed the hard layer that we think that an earlier core got stuck in and we cored into a deeper “acoustically transparent” (in the seismic data) sedimentary package that is ubiquitous in all of the sedimentary basins in this region.
  • Here Marie is labeling our 19+ meter core! This is a very long core and the longest one from this cruise so far. Our team actually has received, labeled, and cut 3 of the 4 cores that have been collected on this cruise. Two of these we did today and we did this longest core in record time! We are really getting into a rhythm.
  • We were so inspired by our success (we finished 20 minutes before our shift ended, we decided it would be nice to have a group photo with the lowest core section, lucky number 13.

2 comments:

Chris Goldfinger said...

Fantastic! You all are doing great! Good luck, this is great to read about as you go.

Patrick Williams said...

looking good out there!