One of the things I have enjoyed most about this cruise is the high volume of stratigraphic data collected in real time. Many other coring platforms have instruments to collect navigational and bathymetric data (images describing the shape of the sea floor), but only a very preliminary assessment of lithology and some physical properties can usually be made on a ship. I briefly mentioned physical properties measurements in IODP Exp. 382 Week 2, but there are four other teams on the JR dedicated to collecting additional data: Sedimentology, Geochemistry, Biostratigraphy and Paleomagnetics.
Each team produces new and pertinent information about each site and while I have a lot of love in my scientific heart for sedimentological and geochemical data, I find myself captivated by the information coming out of the Biostratigraphy and Paleomagnetics labs (Biostrat and Paleomag, for short), which is the focus of this week’s blog. What is so interesting about this work that it warrants an entire blog post? It’s the fact that these data let us travel through time!
It’s not exactly a science fiction jump to hyperspace; rather, the biostratigraphers and paleomagnetists give us the age of our sediment. Because age is a necessary component of any geologic investigation, our geology-minded readers might be wondering what is particularly special about these data. The shipboard work that Exp. 382 scientists do allows us to estimate the age of the cores as we collect them! I think this is amazing because I work mostly with radiocarbon, which requires special instrumentation and weeks of waiting time to get radiocarbon dates. But here on the JR, Biostrat and Paleomag teams work together to constrain ages using shipboard data, sometimes working out the sediment age before the other teams can make their own measurements.
Each team derives an age differently. Biostrat uses the fossils of tiny phytoplankton and zooplankton preserved in the sediment. Each team member specializes in a specific plankton group. Biostrat uses their expertise to identify certain species and their knowledge of many different species allows them to determine when a species existed and how it relates to older or younger species. Ivan, our radiolarian specialist, says its like finding the father then looking for the grandfather and the son. I want to stress that these scientists do this just by looking at these organisms! Of course they have references and colleagues on land to help, but I always marvel at the encyclopedia-level of knowledge contained within the Biostrat team. I talked with Frida, our resident palynologist (one who studies dinoflagellates, pollen and spores) and Yuji, who specializes in diatoms, to help me understand their work. Each biostratigrapher spends hours on the microscope looking at specially prepared slides, but they each have different amounts of work to do before getting to the scope. This ranges from simply smearing sediment on a glass plate with a toothpick, to spending hours at the fume hood working with strong acids. The preparation and microscope time are well worth it when Yuji, Frida, and Ivan, together with their day shift counterparts, Linda and Jonathan, can compare their results to narrow down the age of a core section.
The Paleomag team provides the framework and confirmation for Biostrat. The paleomagnetists are responsible for identifying changes in Earth’s magnetic field through time using magnetic minerals preserved in the sediment. If that sounds more like magic than science, then you’ll be happy to hear that we sometimes refer to the Paleomag team as Paleomagicians! Stefanie, Paleomag team member and veteran Antarctic researcher, says that magnetic minerals act as compass needles as they are deposited at the sea floor, orienting themselves to the Earth’s magnetic field, which periodically flips upside down. Right now, Earth is in the “normal” phase and the magnetic field lines are pointing down at the magnetic north pole; reverse phase is just the opposite orientation with field lines pointing down at the magnetic south pole. A switch in orientation is called a reversal, and it leaves a characteristic signature in magnetic deposits everywhere on Earth. The pattern of reversals acts like a barcode, signifying the cores’ place in time to the paleomagnetists. Assuming surface sediments are zero age and therefore have “normal” orientation, the team can work back through time to match the known pattern reversals and determine the sediment age. The theory sounds straightforward; the practice is anything but. Discontinuous sediment sequences and the absence of magnetic magnetic minerals can complicate a reconstruction. It’s a good thing we have Stefanie and her team mates, Lisa (who literally wrote the book on Paleomagnetism) and Brendan, to do some next-level pattern recognition.
Both teams on both shifts provide the chronological framework for the cores we collect. I recognize that it’s not literal time travel, but it’s the best way to describe the feeling of looking at sediment and knowing that you’re staring ~8 million year old material in the face…or facies (I can’t resist a geology pun). With each age update, I feel like I am hurtling back through time back to a different Southern Ocean. If not a journey through time, then definitely a journey through imagination.