As we arrived at our first study site, there was excitement in the air. We were surveying a site in the Pennell Trough, Ross Sea that may provide clues to how the Ross Ice Shelf retreated in the past (Fun fact: My lab mate, Imogen Browne, is studying the paleoenvironment of the Pennell Trough in the Miocene, ~14-16 million years ago). While we chose this site based on geophysical data, this was also a great water chemistry sampling site. As such, we called this first site “Super Station 1” and deployed three types of instruments/samplers:
CTDs are one of the most common instruments used in oceanography. The name stands for conductivity (salinity), temperature/transmissivity, and depth. While the CTD is a series of sensors that measures basic physical parameters, we also deploy a rosette of Niskin bottles to sample water at different depths through the water column to analyze water for biological (e.g., phytoplankton assemblages) and chemical (e.g., nutrients) parameters. We may not be GEOTRACES trace element rosette experts on this Palmer expedition, but we can hold our own.
The rosette, post deployment in the Baltic Room of the NB Palmer. The Baltic room is enclosed and lets us deploy the CTD in rough weather, and sample the Niskins away from the elements.
On our expedition, we are collecting sediment cores to assess the response of the Ross Ice Shelf to past climate changes. To collect sediments from at and below the seafloor, we deployed a multicorer and a Kasten corer. The multicorer looks similar to the rosette, but with ~8 clear plastic tubes about 1 meter long that, when triggered, collect multiple the upper 1 meter of sediment. The multicore is useful because it enables us to sample the sediment-water interface with little or no disturbance. This is really important for Paleoceanographers trying to reconstruct the last ~1000 years of climate or for regional proxy calibration and 14C reservoir corrections (more on this later). Kasten cores are special gravity cores designed to recover larger volumes of sediment and to be sampled shipboard. The Palmer has Kasten Core barrels between 3 and 9 meters long. The real trick with the kasten core is to determine how much weight to put on so that you collect a long enough sequence, but don’t over penetrate and blow out the sediment-water interface. We use the multicore and the kasten core together to get a complete sediment sequence of the upper 3 to 9 meters of sediment.
A kasten core coming up on the back deck. That red box is what the Marine Technicians (MTs) use to rest the core barrel on while they secure the weight stand.
My onboard research
On this cruise, I am wearing a few title hats: sedimentologist, micropaleontologist, and organic geochemist. My main job is to search the sediments for tiny microfossils called foraminifera – a single cell zooplankton that secretes calcium carbonate shells, called tests; in Antarctica, a lot of the benthic foraminifers (that live on or in the sediments) make their tests out of grains of sand and anything else they can find. We’re really hoping that the sediments we collect contain foraminifers made out of calcium carbonate because their tests record past ocean physical and chemical parameters. For my research, I am sampling the multicores and the kasten cores.
When I sample the multicores, my main focus is to differentiate between living and fossil organisms in the sediments. To do this, I add a protoplasm stain to the samples called Rose Bengal. This bright pink stain enables us to separate the living and recently dead organisms from fossilized organisms (with no remaining protoplasm). This process takes a few days, and I monitor the pH so that I don’t inadvertently dissolve any calcium carbonate. I then wash the fine sediments from the sample, dry the residuals in an oven for 24 hours, and then put the samples into well-labeled vials for future study! Over the years, my advisor has learned that it is best to wash for forams on the ship because Antarctic sediments and their overlying ocean waters can be corrosive to calcium carbonate. You can return home to find sediments with little or no remaining calcium carbonate.
Washing the multicore samples: You can see the stained living to recently dead organisms in this sample! Two organisms from this sample included a bivalve (top) and a benthic foraminifer (Globocassidulina spp.)!
When we sample the kasten cores, my first objective is to collect samples for radiocarbon dating. These samples will be analyzed in Dr. Brad Rosenheim’s USF lab. Radiocarbon dating is extremely important because it enables us to determine when the sediments were deposited. After we sample for radiocarbon, we sample for organic and inorganic geochemistry and micropaleontology, which will help us understand past ocean temperatures and paleoenvironments.
Also on the boat…
One thing that is great about this research expedition is that there are a lot of students from different PI groups at different universities. Let’s hear from some other students about their first day of sampling!
Environmental Scientist: Alyssa Cotten
Alyssa is an undergraduate student in Dr. Wade Jeffrey’s lab at the University of West Florida. Her research focuses on quantifying bacteria and phytoplankton production (a fancy word for growth) using radioisotope tracers. She sampled water from the top few niskin bottles. She also sampled one of the multicores to test her method in the sediments. Her favorite thing about life on the Palmer is her roommates (author’s note: she didn’t feel pressured into saying this because I am one of her roommates) and seeing snow for the first time!
Alyssa in the “Rad Van”, a shipping container on the Helo Deck where all radiotracer work is done. It is really important to avoid tracer contamination onboard because some scientists (like me) are looking at natural levels of the same elements.
Marine (Geomicro)Biologist: Caleb Boyd
Caleb is a first year Ph.D. student studying geomicrobiology with Dr. Brandi Kiel Reese’ at the University of South Alabama and Dauphin Island Sea Lab. What a way to start out a Ph.D.! For his project, he is sampling the CTD, multicore, and Kasten core – the whole suite of tools we deployed. When he samples, Caleb “protects the samples from himself” – making sure that his microbiome does not contaminate the samples. In their lab onboard the Palmer, Dr. Kiel Reese’s team set up a “clean bubble” by hanging plastic sheets around their equipment to prevent contamination. Caleb will determine the metatranscriptomics (broad scale view of the active microbial community), cell counts (in a known sample volume), and will even grow (called culture) some of the microbes to determine what lives in the water/sediment. This type of research is important to understand the outsized role that tiny microbes play in nutrient cycling and larger biogeochemical cycles. Besides meeting new people and learning about different research fields , Caleb’s favorite part of life on the Palmer is rocking and rolling in the Southern Ocean’s huge ocean swells.
Caleb with his multicore sediments.
Over the last few days, we have sampled another superstation and took an add Kasten core! For now, I’m staying busy washing sediments in my search for living benthic organisms and microfossils. Next stop: McMurdo, Station!