Chief Scientist and Chief Rock
The past 48 hours (approximately) have been relatively calm as far as work goes since some bad weather (35-45 knot winds) has halted over-the-deck operations. However, we were able to maintain station long enough (3.5 hours) for a rosette CTD and Amelia’s water pumping, which allows her and her colleagues at USF and elsewhere to collect archaea in different water masses and compare their population genomics. The 48 hours before these last two shifts (and I mean the full 48 hours) were packed with core sampling and collection. So as Michelle recently blogged, those days when we all count sleep as our “fun activity” of the day definitely come after these busy, but incredibly rewarding and exciting days and nights.
Good coring weather
When the night-shifters woke up on the 21st, we saw two 3-meter kasten cores open on the table, being sampled simultaneously by the sizeable group of day-shifters. They had already taken Amelia’s DNA samples, foraminfera and organic geochemistry samples via syringes, and almost completed the diatom sampling for Amy. They had also brought up our biggest JPC to date: 13 meters! All of these cores were taken at the same station, which had a lot of interesting diatom-rich layers that we were able to see in the open kasten cores and via the magnetic susceptibility in the JPC that we ran on the 22nd. The day-shifters were still wide awake and active when we came to relieve them, and we were excited to dive in to these new samples. Continue reading
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
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
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
[Check out the Facebook page for more photos that we couldn’t squeeze into the blog entry. This link to the album will work even for those without a Facebook account.]
Gene Domack, one-man supergroup
Although most of our time in Hobart was allotted to preparing the ship to set sail, we were able to spend a day looking at the geology and ecology of Tasmania with Gene Domack, who has done significant research throughout Tasmania since 1988. On Monday, we ventured outside of Hobart to Mount Field National Park in Maydena. We went to Mount Field to see the magnificent Russell Falls and the great exposure of certain formations of the Parmeener Supergroup. We discussed how the Supergroup sits on the central plateau of Tasmania, which formed during the Late Paleozoic accretionary event when Gondwana assembled. The Parmeener Supergroup ranges from Carboniferous to Jurassic in age, and includes the last evidence of ice at sea level on the planet until the Cenozoic.
At this location, we were standing on the Permo-Triassic boundary, which was the time of the biggest extinction event on Earth and marked the transition between the Paleozoic cool, humid “icehouse” environment to the Mesozoic warm, arid “greenhouse” environment. The Parmeener Supergroup is analogous to the Beacon Supergroup in Antarctica, along with other Gondwanan stratigraphy in Africa, India, and South America. By studying this stratigraphy, we can see the connections between continents when they were together and determine past climates and past continental positions.
The Supergroup begins with a tillite layer that we saw in an outcrop outside of Maydena, which is Carboniferous in age. Above that is a fossiliferous mudstone that has been dated to 294 +/- 7 million years, which is the base age of the Permian and may also contain evidence of 42,000-year Milankovich cycles. In the stratigraphy, we see that the tillite immediately transitions into the shale layer rich in Tasmanities, which are green algal cyst deposits that live in an open marine pelagic environment. Analyzing the stratigraphy and fossil evidence allows us to determine that the transition between and glaciated environment and a marine environment was immediate in geologic time. Continue reading