December 14, 2010 Muddy Buddies Part 1
One of the reasons I so enjoyed and appreciated the 2010 International Continental Shelf Survey last summer was because of the wide range of science that was undertaken on the cruise. Every day I could see something new and learn much about geology, oceanography, meteorology, climatology, ice studies, biology, chemistry, physics, navigation, computer systems, instrumentation, marine sampling technology, and the gear and techniques used to travel in, survive, and understand the Arctic. Still, the mission had three priorities and all other science had to be done in a way that wouldn’t interfere with the primary objectives. The main goal of the cruise was to collect seismic data. Secondary to that was collecting high-resolution bathymetry data via multibeam sonar. These two data sets could be collected simultaneously as the Healy broke ice and collected multibeam data while the Louis followed, towing its seismic array in the open channel. The third objective was to collect physical sea-floor samples. This required special opportunities, though, as each sample collection involved many hours of ship stoppage. Ironically, even though the Healy was equipped for bottom sampling, that activity was mainly driven by the Louis. If the Louis needed to repair its sonar and we thought there was sufficient time then we would take a bottom sample. But if the Louis needed extended time for repairs or to head off on a separate course for a few days we would resume our sonar work since it had priority over bottom sampling. In the end collected sea-floor core samples at 5 sites. During those windows of opportunity samples were collected via gravity or piston coring, trimmed to manageable size (150cm or less segments), and stored under refrigeration until they could be returned by refrigerated truck to the US Geological Survey (USGS) lab in Menlo Park, California where they awaited the detailed analysis that began last week.
During last week’s workshop I learned about many types of data that can be recovered from sea-floor core samples. Cruise Chief Scientist Brian Edwards, a USGS Marine Geologist & Sedimentologist, organized and headed up the activities & data collection. We were joined by USGS scientists Brian Buczkowski (geologist & archivist), John Pohlman (biogeochemist), Pat Hart (geophysicist), &Tom Lorenson (geochemist.) I also had the chance to meet with USGS micropaleontologist John Barron one day (more on that later.)
The first step in the process is to take non-destructive geophysical measurements from each core. This is done on a technically advanced piece of equipment called a Multi Sensor Core Logger (MSCL). Without disturbing the sediments, it measures the density, sound speed velocity, and magnetic susceptibility along the length of the core. The core section is placed on a rail where a calibrated pusher sends it through the various sensors. Laser beams monitor the position of the core as it begins passing through each sensor and readings are correlated to specific parts of the core to millimeter resolution by constant digital comparison of the readings to the position of the pusher. These readings are computer-recorded into output files that are later organized into a spreadsheet. Finally, the spreadsheet is uploaded into a master database that contains all of the summary data and archival nomenclature for each core section. These MSCL data help with the initial interpretation of the cores, guiding scientists to potential changes in sediment layers and identifying gaps (if present) in a core section.
For the rest of the information to be retrieved the core is first split into two halves. A specialized machine called a core splitter pulls two razor-sharp hooked carpet knives through the plastic core liner along each side. Then the sediment inside is split with a wire knife &/or spatulas, depending on its consistency. The two halves of the opened core are compared, with one being identified as the working half (from which more samples will be taken) while the other becomes the archival half (generally, if one half is in better shape then it is saved as the archival portion.) The best looking half gets one more ride through the Multi Sensor Core Logger to get photographed. A camera scans the split core surface as it slowly passes through the MSCL under a high-intensity lamp. The high-resolution photograph is also calibrated to a millimeter scale so it can be compared with the other sensor data and samples taken from the working half. On every core, measurements and samples are always referenced from the top of the core section in centimeters for consistency and to correlate different types of data to the same level in the core. One of the jobs I was privileged to have during the core workshop was photographing the core samples- certainly different than the photos of wildlife, people, and scenery I’m used to taking!! Finally, the archival half is re-sealed into a storage tube & carefully labeled & attributed in the database before its return to the giant walk-in storage refrigerator.
Next: Sampling Plans & Core Descriptions! That’s all for now- Bill