A Chemical Stopwatch for Tracking Carbon in the Ocean

The world’s oceans carry huge amounts of life and play an enormous role in the earth’s carbon cycle. To make accurate predictions about climate change, then, scientists need to look to the seas.

Professor Gillian Stewart of Queens College and The Graduate Center, CUNY, and recent Ph.D. graduate Yi Tang have studied the behavior of polonium-210, a radioactive isotope, in different parts of the ocean. Radioisotopes can act as tracers to help researchers understand how the ocean acts as a “biological pump” for carbon, taking in carbon dioxide from the atmosphere. This, in turn, will give a clearer picture of the way carbon cycles through the planet.

Stewart and Tang’s most recent paper, published in Global Biogeochemical Cycles, was featured as an “Editor’s Highlight” by the American Geophysical Union.

Polonium can latch on to carbon particles at the ocean’s surface, and can accumulate in living organisms like plankton. Both the particles and deceased organisms will eventually sink, taking the polonium with them. Because scientists know how quickly polonium-210 radioactively decays, they can use the isotope like a stopwatch to track the rate that carbon, in the form of particles or biomass, leaves the ocean’s surface.

For their work, Stewart and Tang teamed up with GEOTRACES, an international effort to learn more about the sources and cycles of trace elements in the oceans via research cruises that crisscross the seas.

During her graduate studies Tang had the opportunity to join in on a GEOTRACES expedition. The 70-person crew set out from Portugal and spent 47 days sailing through the north Atlantic before docking in Newfoundland. Between taking samples of water and particles and preparing them for lab work, Tang said, she found time to enjoy meals with her crewmates and watch sunsets from the ship’s deck.

Ph.D. student Yi Tang in white coat and rubber gloves with materials in a lab
Ph.D. student Yi Tang aboard the research vessel Pourquoi Pas? (Credit: Maxi Castrillejo)

Back in New York, Tang analyzed her samples in Stewart’s lab. For her thesis she took a close look at the way researchers calculate carbon flux using polonium. The usual model is too simplified, Tang said, and uses assumptions that aren’t true in reality. With a more careful understanding of how these cycles work scientists will be able to create better projections of how the oceans will react to our changing climate.

“The ocean is not under a steady state,” Tang said. “There are currents, and the chemistry is not stable at all. Certain assumptions may work for one tracer but not for polonium.”

Beyond SUM

Work By

Yi Tang (Ph.D. student, Earth and Environmental Sciences) | Profile 1
Gillian Stewart (Professor, Earth and Environmental Sciences) | Profile 1 | Profile 2