Ocean sediment cores provide a glimpse into deep time

Theresa on a recent cruise on the Oceanus.
Photo credit: Natasha Christman.

First year CEOAS PhD student Theresa Fritz-Endres investigates how the productivity of the ocean in the equatorial Pacific has changed in the last 20,000 years since the time of the last glacial maximum. This was the last time large ice sheets blanketed much of North America, northern Europe, and Asia. She investigates this change by examining the elemental composition of foraminifera (or ‘forams’ for short) shells obtained from sediment cores extracted from the ocean floor. Forams are single-celled protists with shells, and they serve as a proxy for ocean productivity, or organic matter, because they incorporate the elements that are present in the ocean water into their shells. Foram shell composition provides information about what the composition of the ocean was like at the point in time when the foram was alive. This is an important area of study for learning about the climate of the past, but also for understanding how the changing climate of today might transform ocean productivity. Because live forams can be found in ocean water today, it is possible to assess how the chemistry of seawater is currently being incorporated into their shells. This provides a useful comparison for how ocean chemistry has changed over time. Theresa is trying to answer the question, “was ocean productivity different than it is now?”

Examples of forams. For more pictures and information, visit the blog of Theresa’s PI, Dr. Jennifer Fehrenbacher: http://jenniferfehrenbacher.weebly.com/blog

Why study foram shells?

Foram shells are particularly useful for scientists because they preserve well and are found ubiquitously in ocean sediment, offering a consistent glimpse into the dynamic state of ocean chemistry. While living, forams float in or near the surface of the sea, and after they die, they sink to the bottom of the sea floor. The accumulating foram shells serve as an archive of how ocean conditions have changed, like how tree rings reflect the environmental conditions of the past.

Obtaining and analyzing sediment cores

Obtaining these records requires drilling cores (up to 1000 m!) into deep sea sediments, work that is carried out by an international consortium of scientists aboard large ocean research vessels. These cores span a time frame of 800 million years, which is the oldest continuous record of ocean chemistry. Each slice of the core represents a snapshot of time, with each centimeter spanning 1,000 years of sediment accumulation. Theresa is using cores that reach a depth of a few meters below the surface of the ocean floor. These cores were drilled in the 1980s by a now-retired OSU ship and are housed at OSU.

Theresa on a recent cruise on the Oceanus, deploying a net to collect live forams. Photo credit: Natasha Christman.

The process of core analysis involves sampling a slice of the core, then washing the sediment (kind of like a pour over coffee) and looking at the remainder of larger-sized sediment under a powerful microscope to select foram species. The selected shells undergo elemental analysis using mass spectrometry. Vastly diverse shell shapes and patterns result in different elements and chemistries being incorporated into the shells. Coupled to the mass spectrometer is a laser that ablates through the foram shell, providing a more detailed view of the layers within the shell. This provides a snapshot of ocean conditions for the 4 weeks-or-so that the foram was alive. It also indicates how the foram responded to light changes from day to night.

Theresa is early in her PhD program, and in the next few years plans to do field work on the Oregon coast and on Catalina island off the coast of California. She also plans to undertake culturing experiments to further study the composition of the tiny foram specimens.

Why grad school at OSU?

Theresa completed her undergraduate degree at Queen’s University in Ontario, followed by completion of a Master’s degree at San Francisco State University. She was interested in pursuing paleo and climate studies after transformative classes in her undergrad. In between her undergraduate and Master’s studies she spent a year working at Mt. Evans in Colorado as part of the National Park Service and Student Conservation Association.

Theresa had already met her advisor, Dr. Jennifer Fehrenbacher, while completing her Master’s degree at SF State. Theresa knew she was interested in attending OSU for grad school for several reasons: to work with her advisor, and to have access to the core repository, research ships, and technical equipment available at OSU.

To hear more about Theresa’s research and her experience as a PhD student at OSU, tune in on Sunday, June 10th at 7pm on KBVR Corvallis 88.7 FM, or listen live at kbvr.com/listen.  Also, check us out on Apple Podcasts!

Print Friendly, PDF & Email

Leave a Reply

Your email address will not be published. Required fields are marked *