What exactly does a planktic foraminifera biostratigrapher do?

Adriane here, reporting once again from the beautiful Tasman Sea!

Double rainbow in front of the ship after a rainstorm.
You may recall from my previous post that I am currently sailing the RV JOIDES Resolution (the JR), a research vessel equipped with a drill rig that is used for scientific ocean drilling. During these scientific expeditions aboard the JR, a team of about 30-35 scientists and several crew members (the JR can hold a maximum of 130 people) drill sediment from the seafloor. Everyone on the ship has a job to do, and in this post I’ll explain what my role is while sailing in the beautiful Tasman.

I am sailing as a planktic foraminifera biostratigrapher (click here to learn more about what that means, and here to read more about how we use fossils to tell time) or someone who uses fossils (‘bio’) to tell time from the rock record (‘stratigraphy’). Altogether, there are 9 paleontologists on the ship. Some of us are here to tell the other scientist what age the sediments are that we’re drilling into, and some are using fossils to interpret paleobathymetry, or the water depth of the Tasman Sea at different times in Earth’s history.

Every scientist’s role on the ship is vastly important, but the first thing everyone wants to know as sediment cores are being drilled and brought onto the ship is how old this sediment is. This is important for a few different reasons: 1. There are specific intervals in Earth’s history that we (the scientists on the ship) want to drill into; 2. With age, we can tell what was going on in the geologic past in the Tasman Sea and further interpret the plate tectonic movements and environments when the sediment was deposited, and 3. We can modify our drilling plan including changing out the drill bits, slowing down the drilling, or speeding up the drilling process to best capture key intervals in Earth’s history. Thus, being a biostratigrapher is initially a very important job, and one that can affect the drilling operations on the ship. That’s why there are four main fossil groups that we use to tell time: the calcareous nannofossils (which are REALLY tiny), the planktic (and in this case, the benthic) foraminifera, siliceous radiolarians, and pollen spores. All of the fossil groups are important to have, as there are intervals in the cores where one or two fossil groups may disappear, or there may only be planktic foraminifera in one sample, etc.

But enough about biostratigraphy, now to show and tell you the entire process we go through when we receive a core on the ship!

The first thing that happens when a core is pulled up onto the core deck is that an announcement is made, such as ‘Core on deck!’. I then put on a hard hat and safety glasses and grab a bowl to collect the core catcher sample (the end piece of the core that literally keeps the sediment in the pipe as the core is brought back to the surface). The core catcher sample is the very last 10 centimeters of the core that is given to the paleontologists to analyze for age. The technicians bring the core from the drill floor to the core deck, where the core is cut into sections. While the core is being cut, another technician is given the core catcher to disassemble, remove the sediment, and give to the paleontologist.

In the first image, the technicians are bringing the core that has just been brought onto the ship onto the core deck. While 4-6 people wipe off, measure, and cut the core into sections, another person disassembles the core catcher and removes the sediment that is inside (center image). In this photo, the sediment is relatively hard, or lithified. When the core catcher sample has been removed and measured, part of it is given to the paleontologists so we can do biostratigraphy (right image).

Once I have the sample, I take it back inside to process. If the sediment is very soft, I simply rinse it over a screen to remove small particles (refer to my previous ‘From Mud to Microfossils: Processing Samples’ post). But recently on the expedition, the sediment we are recovering has been very hard. In this case, the core catcher sample is cut into thin slices using a rock saw, then small pieces are shaved off of a slice using a sharp-edged tool. These smaller pieces are crushed with a mortar and pestle for a few minutes.

Left image: the core catcher sample that was obtained here was cut into thin slices. One of these slices is then cut into smaller pieces using a small tool (center image). The smaller pieces are then crushed into finer grains using a mortar and pestle (right image). Surprisingly, most of the tiny fossils survive this process!

The sediment is then rinsed over two screens: a 2 millimeter (mm) screen to hold back the larger particles, and a 63 micrometer (μm) screen to catch the microfossils. The >2 mm rock pieces are then crushed again until there is enough particles in the 63 μm screen to analyze for planktic foraminifera. The sediment, which we call the residue at this point, is then put into filter paper on a stand to drain out the extra water. The filter paper and residue are then put onto a hot plate to dry (yes, there have been a few times when the paper has burned!).

In the left image, the pulverized sample is rinsed over a screen several times. Once there is enough sediment, at this point called the residue, to work with, it is put into a paper filter to dry (center image). When most of the water has dripped out, the filter paper and wet residue is then placed on a hot plate to dry (right image).

This is my microscope that I have used (and it’s really nice!) for the past 5 weeks at sea. Notice the paintbrush, jar of water, green dye, slide (white and black rectangular piece of cardboard in an aluminum holder), and black tray with the dried residue sprinkled across. When I find a marker species that tells me something about the age of the sediment, it is picked using my paintbrush and put onto the slide. In this sample, I found an important marker species, named Morozovella crater. The top right image is a picture taken through the microscope of the specimen dyed green. The bottom right image is a picture of a different specimen of the same species taken using an SEM (which is basically a fancy, very expensive camera used to photography very small fossils and minerals).
After the residue is dry, it is put into a small plastic bag with a label indicating exactly where it came from within each core. At this point, the residue is ready for analysis! At my desk, I have a microscope, a small tray, very small paintbrushes for picking very small fossils, a jar of water, and green food dye. Because the microfossils that I look at are made of calcite, they are very bright under the lights in the microscope. Dying the fossils a green color cuts down on the reflectance of light off the foram’s shells, and enables me to see the details of the fossil necessary to identify it to the species level.

There are usually many different planktic foraminiferal species in each sample, but there are only a few that I usually look for that tell me about the age of the sediment. These are called ‘marker species’. The geologic time at which a marker species evolves or goes extinct has been calibrated by previous scientists before me over several decades, so when I find a species, or when a species suddenly disappears, I have a chart that I use to look up when that speciation or extinction event happened.

Once I have a datum (reference point of time) and an age estimate for the residue sample I’m looking at, I write this information on a big white board in the paleontology lab. All of the other scientists look at this board frequently to determine the age of the sediment that is being brought up.

Education and Outreach Aboard the JR

Every IODP expedition has an education outreach coordinator that sails with the crew and scientists. This person’s job is to blog, post photos on social media outlets (Facebook), and conduct ‘Ship to Shore’ linkups. These are scheduled events with colleges, university, and K-12 schools where the education outreach coordinator gives the viewers a live tour of the ship and the activities that are going on. Because every expedition is funded by public monies from several countries, it is our responsibility as scientists to engage with the public and tell you all what we’re doing and what we’re learning. I’ve participated in a few ship to shore linkups already, and have really enjoyed talking with students of all ages about fossils, what we’re finding in the Tasman Sea, and how we use the fossils to tell time!

If you are an educator and want to participate in a Ship to Shore video event, click here to sign up!

Leave a Reply