As Michelle’s most recent blog stated, our past couple shifts have been hectic while we processed our first five cores. The jumbo piston core (JPC) and jumbo gravity core (JGC) were both 20-foot long barrels, each returning approximately 10 feet of sediment excluding the 1-foot trigger core associated with the JPC. The JGC is similar to the kasten core in that it is allowed to “free-spool” on the winch as it nears the ocean floor during its descent and then uses its own weight to penetrate the sediment.
Dan Powers checks the bomb as we prepare to deploy the JPC
The JPC is rigged a little differently, with a counter-weight (the aforementioned short trigger core) suspended below a triggering mechanism that holds the main JPC barrel, the weight (known as “the bomb”), and a coil of slack line. When the trigger core hits bottom, the main JPC barrel is released and free-falls the remaining distance into the sea floor. This method generates more momentum than free-spooling a core on the winch line, thereby increasing the depth to which the core may penetrate. The coring system on the Palmer can support JPCs up to approximately 25 meters long, but other vessels have successfully deployed JPCs that recovered as much as 80 meters of sediment!
The piston that gives the JPC its name ends up at the sediment-water interface if the core is successful and is designed to improve recovery. The way this works is analogous to putting a drinking straw into a glass of water and covering the top of the straw with your finger to take water out of the glass using suction. Even though our cores have been relatively short so far, recovery has generally been good. The recovered sediment is contained in the 4-inch diameter PVC liner that fits in the JPC barrel. When the core is retrieved, we extrude the liner and cut it into 10-foot sections.
Unfortunately, we have to patiently wait to do most of the processing on these cores because if we cut them open now, we won’t be able to securely ship them to the USAP core repository in Florida State University for final processing. Therefore, the only sediment we get to see on-board now is the sediment in the cutter nose and core fingers (the very bottom of the core), the sediment between the sections of PVC liner we cut, and whatever mud is on the coring device. Continue reading
(and the Grease, and the Salt Water)
The past week has been a busy one. We have secured 3 full kasten cores, 1 jumbo gravity core and 1 jumbo piston core (with 1 accompanying trigger core). A kasten core has a rectangular barrel that is deployed via gravity. It penetrates 2-3 meters into the sediment and can be opened on the ship so we can describe the stratigraphy, take photos, and collect samples. Each kasten core takes about 12 hours to process, depending on the length. First Gene has to describe the core (color, layers, sediment composition), then Tasha will take pictures. After that, someone on shift puts on the lab coat and nitrile gloves and takes samples for DNA/RNA.
The next round of sampling includes taking sediment for organic geochemical analysis and foraminifer microfossils (fossils of calcareous single-celled animals). These samples will be used for a suite of geochemical analyses to determine past temperature, productivity, and oxygen content, among other things. While geochem and foram sampling are happening on one side of the core, another person is sampling for physical properties on the other side. If there is enough mud left, we will also take pea-size samples for diatom analysis and 5-cm interval samples for radiocarbon. Believe it or not, the first layer of sampling on a 2-3 m core takes 7-8 hours with planning, putting together the core barrel, sampling, cleaning sponges and utensils, labeling bags, and sample storage/inventory. These are the days when the marine geology group spends 12 hours on their feet. Continue reading
Kelsey and Gene rocking out
We started for the Totten Glacier area, our main study area, at around 11:45am GMT on Wednesday, February 7th. Our shift on Thursday the 8th began with processing the dredges, starting with our most recent dredge that targeted the Eocene-Oligocene boundary for the second time (importance of that temporal boundary is discussed below). First, we cleaned each rock individually from small pebble to boulder size. We arranged them on a table in the dry lab into the three rock categories (igneous, sedimentary, and metamorphic) and then roughly subcategorized those groups. Once the rocks were dried and laid out on the table, Gene helped us finalize our sorting, and discussed what we found. The sedimentary rocks are the most important because they can tell us about past depositional environments. After we finalized our categories, we counted, photographed, and packaged the samples (1,029 total!). This took us about 9 hours to complete, leaving four dredges left to process (with each dredge having 7 to 394 total samples, which all went a lot quicker!)
Sunrise on the back deck
That same day, we had a science talk regarding our dredging and seismic results, along with overall Cenozoic climate change trends. Amelia discussed the trend of overall cooling that we have seen over the Cenozoic. This was determined using oxygen-18 isotope records, establishing an ice volume record throughout the Cenozoic. In 2000, magnesium-calcium paleothermometry was used to isolate sea water temperatures from the ice volume record, showing a 12°C overall cooling since the Mesozoic. From these curves, clear climate transitions were shown at the Eocene/Oligocene boundary (~34 million years ago), the Middle Miocene (~14 Ma), and the Pliocene/Pleistocene boundary (~5 Ma). It is still being debated what is causing this cooling, but two current hypotheses are 1) ocean heat transport due to the opening and closing of oceanic gateways and 2) overall decreasing atmospheric CO2 due to changes in seafloor spreading, uplift, and weathering. Continue reading
We are just about 6 nautical miles from the edge of the Totten ice band and should be able to break through the sea ice into some ice-free water adjacent to the coast by this evening. Our watch shifts now demand a higher level of attention because we are in un-chartered waters; there is no pre-existing data from this area. Every seafloor feature that shows up on the screen on the Knudsen bathymetric profiler has never been seen before. NBP14-02 will be the first cruise to survey the seafloor and collect geological and physical measurements of the sediment and ocean currents.
Now, all planning is in overdrive. At the transition between shifts, there is usually a PI meeting at the navigation table or in the Chief Scientist’s room. These meetings include deciding which sites to hit first, which group will run their instruments and in what order. As we steam toward Totten Glacier, the researchers running the seismic instruments are planning their lines (the distance between two waypoints on which they will make their measurements).
These images are very important because they will be high-resolution images of the ocean bottom and the sub-bottom down to about 400 m. That is tens of millions of years of a sediment record in one picture. The seismic images show the various layers and points of contact between geologic periods. For example, we may be able to see the boundary between the Eocene and Oligocene. Continue reading
Mertz Trough sea ice (click to enlarge)
When we started our shift, the multichannel seismic streamer had just been deployed to start its 16-hour survey. This is the maximum continuous operational time for this instrument because our marine mammal observers, Tasha Snow (USF) and Andrea Walters (University of Tasmania), have to be on watch while it’s in the water, and each of them is only permitted to do an 8-hour shift. We anxiously awaited the data to be processed by Bruce Frederick and Sean Gulik (University of Texas at Austin), our resident seismic experts on the night shift.
These data are very important not only for determining core and dredge sites on our cruise but to add to the support of an IODP (Integrated Ocean Drilling Program) proposal for this area. The proposed drill cores will be approximately 80 meters in length will help scientists to observe and analyze how climates (particularly ice sheets) respond to increased CO2. The specific goals of the proposal are to address the timing of “the Eocene-Oligocene ice advance (~34 Ma), the mid-Miocene climate transition (~14 Ma) and the earliest Pliocene warmth and climate fluctuations (~5 Ma).” Everyone was very excited about the data that we collected and now it was time to pick dredge locations!
PIs reviewing the processed seismic data
Although our watch was dominated by this seismic data and activity, I had a lesson with Caroline Lavoie (Universidade de Aveiro), one of our multibeam specialists. We discussed how to process the data that we were receiving hourly from the multibeam system and about the CARIS system in general, which we use to process the data. Continue reading
There is so much planning that goes into making these research cruises a reality. Multiple conference calls, pre-cruise meetings, travel and lodging logistics, coring and site survey selection- all of these things spread over years. All that planning gets us on the ship … and then we have to adjust many well-laid ideas to suit the environment. Amelia tells us that as a PI (Principal Investigator), it’s not enough to have a Plan B; you have to have Plans A through Z.
So far, we’re on Plan F
Weather and ice conditions change so fast down here, so all the PIs need to be flexible with their own sampling strategies as well as accommodate each others’ scientific objectives. That means when we finally get into the ice, plans change; the decisions that dictate those plans are carefully weighed and executed. Going into this cruise, I knew there must be a whole list of reasons for choosing a core site. Now, 8 days in, I am finding out just how many factors contribute to our PIs’ decision and I am astounded at their combined knowledge. Continue reading
Today marks the beginning of our sixth day underway and the crossing into the beginning of an entirely new world. We crossed 60 degrees south and have committed to continuing our travel directly south to the Mertz glacier; we expect to make it to the edge of the continental shelf on the morning of the 4th. To prepare us for our arrival in East Antarctica and for the beginning of a flurry of science that will be taking place, we listened to a couple of brief science talks about past science and our current objectives at the Mertz glacier.
And after that, we didn’t let the penguins drive the boat any more…
One of our objectives will be to acquire geophysical (seismic) survey data that will satisfy the requirements for future deep sediment drilling in the area. Seismic surveys will be conducted using two air guns that transmit sound pulses to the sea floor. This energy is powerful enough to penetrate 1 or 2 kilometers down into the sediment and underlying bedrock basement. When the sound waves encounter density changes in the stratigraphic layers (e.g. transitions from clay to bedrock), some of the energy reflects back up to the surface of the ocean where we have a seismic streamer (array of hydrophone receivers) that will detect the sound and record it.
Vessel telemetry, 3.5 kHz sub-bottom profiler, multibeam sonar, and other assorted toys
We then translate the recorded sound to an image that will be used to create a map of the sediment layers below the seafloor. The map is based solely on the time it took for the sound to travel from the guns into the sediment and back to the receivers. These maps of the sub-bottom have many applications. Continue reading