Volume 13, Number 3, 2005
Most people think of libraries as repositories of books and online databases. But, Katharina Billups, assistant professor of oceanography in the College of Marine Studies, makes use of a different kind of library—one that contains a repository of sediment samples of the ocean floor. These samples, or ocean cores, are crucial to her work in understanding how the ocean has changed over time and its link to climate changes.
Ocean cores are obtained by pushing a long, hollow rod deep into the ocean floor. When the rod is pulled out, it contains a cylinder of the sediments of the ocean in the chronological order in which they were laid down. The cores also contain the fossilized remains of marine organisms.
“I am especially interested in determining how quickly climate changed in the past and the mechanisms of that change,” Billups says. “If we study how the ocean and climate interact when only natural changes were a factor, then we can use this information to help unlock the mysteries of how our climate may change from human activity.”
Billups currently is focusing her efforts on a region in the subtropical Atlantic, off the coast of Florida, during a time period that included several interglacial and glacial events. This project, funded by the National Science Foundation, is looking at climate changes that occurred on a time scale of 1,000 years, or millennial scale, beginning about 400,000 years ago and going back to 900,000 years ago.
An understanding of past climate conditions is becoming increasingly important as scientists try to assess the rate of natural climate change, determine the sensitivity of the Earth system to variations in climate-forcing factors and evaluate numerical models that simulate climate change.
Sediments accumulated very rapidly at the study site in the subtropical Atlantic, providing a clear picture of past climate change. In addition, the Gulf Stream, which plays a major role in the modern climate system, is nearby. The Gulf Stream is part of a larger gyre, or ocean circulation pattern, that moves warm water from the tropical Atlantic to the North Atlantic.
“The Gulf Stream is one of the reasons that it is much warmer in Europe at a latitude of 50 degrees north than it is here at the same latitude in the United States,” Billups says. “It’s possible that the Gulf Stream also had an impact on past climate conditions.”
Billups obtains her data from the fossilized shells of foraminifera (or forams), one-celled marine organisms found in the core sample. Much like using a colander to strain spaghetti, Billups places the core sample into a sieve and washes the sediment off the forams. Once the forams are cleaned, she puts them under a microscope and selects samples for testing. These forams then are dissolved in acid, and the resulting carbon dioxide gas is analyzed on a mass spectrometer, an instrument that measures the masses of atoms and molecules in a material.
In the case of forams, the mass spectrometer provides the ratio of oxygen-18 to oxygen-16—two varieties of oxygen atoms called isotopes—in their shells. The isotope ratio in the shell is dependent on two things, the amount of ice that was present at the poles and the temperature of the water in which the organism lived.
“For example, during periods of glaciation, seawater has a higher concentration of oxygen-18,” Billups says. “The water molecule with the lighter isotope, oxygen-16, tends to evaporate more easily and then falls as snow at the poles and gets locked up in the ice.
“If the shells are high in oxygen-18, then the forams lived during a period of glaciation, in cold water or both. The tricky part is being able to distinguish between these two effects.”
Billups says she stumbled into paleoceanography, which is the study of ocean history, as a senior geology major in college. “I was sitting in a seminar, and somebody gave a talk on climate change and ice-core records,” she says. “And, then, I got a chance to work in a lab with a professor who did climate change-related science.” She says she’s been hooked ever since.
She likens herself to a detective trying to put the pieces of evidence together as she constructs these ancient records of the ocean’s climate. She says the work is stimulating and creatively challenging, as she figures out how the pieces might fit together.
“You can’t just set up an experiment and test it and find out if you are right or wrong,” Billups says. “You can only generate good data and interpret that data based on other observations. Your interpretations of that data may change as more information is collected. But, it’s just kind of fun to think about how the pieces fit together given the assumptions that you have to make.”
In addition to her research, she says she also enjoys teaching a course that introduces students to paleoceanography. “It’s fun to see the ‘light bulbs’ come on and get the students excited and interested in a field that’s not traditionally taught,” she says.
Billups earned her bachelor’s and master’s degrees in geology from the University of California at Davis and her doctorate in Earth sciences from the University of California at Santa Cruz. Before joining the UD faculty in 2000, she completed a postdoctoral fellowship at Harvard University.