Fighting for a “crazy” project

For an ambitious research project, Chinese environmental scientist Chuxian Li has found the ideal environment at the Oeschger Centre. She wants to determine the role of the Southern Ocean in the carbon cycle.

"I usually have a Plan B in life," says Chuxian Li, "but I do my best to achieve Plan A." However, sometimes the alternative trumps the original goal. For example, the young Chinese woman initially wanted to land a Marie Curie Fellowship for postdocs. Her plan was to use this EU funding to go to Cambridge and study the role of westerly winds in the Southern Hemisphere in relation to the ocean's absorption of CO₂. But then she ended up at the Oeschger Centre with a grant from the Swiss National Science Foundation (SNSF). Now she’s conducting research in Bern on whether the Southern Ocean functions as a CO₂ source or sink.

That's the short version of this story about an ambitious climate researcher. But let's take it one step at a time. Chuxian Li grew up on the coast of southern China. In her humble village, studying seemed unthinkable for most young people, especially girls. But Li's family had once been more affluent, and they supported their daughter's ambitions. So she moved to Chongqing, a city of 30 million, and attended Southwest University — first for a bachelor's degree in environmental engineering and then for a master's in environmental science. She wrote her master's thesis on the accumulation of mercury in zebrafish. As it would turn out, measuring mercury in the environment would become her future research topic.

Award for talented young female scientists

At a conference in China, Chuxian Li met a leading specialist in the field. He offered her the chance to write a doctoral thesis in his lab at the University of Toulouse, and she jumped at the opportunity. Equipped with a Chinese scholarship, she moved to France in 2015. So how conducive is a foreign PhD to a career in China? "It helps a lot," says Chuxian Li, "especially if you work with the world's best in the process." In Toulouse, she learned how to measure mercury isotopes in peat soil, a natural environmental and climate archive. The title of her dissertation was: "Holocene Variability of Atmospheric Dust and Mercury in the Southern Hemisphere." Chuxian, who characterizes herself as "curious," "persistent" and "a bit crazy," also attracted attention outside her university in France. In 2019 she was awarded a L'Oréal-UNESCO Prize for Women in Science.

The next stop on Chuxian Li's academic European tour was Sweden. At the University of Agricultural Sciences in Umeå, she worked as a postdoctoral researcher on projects related to mercury isotopes in boreal peat soils and their role as a climate archive. During this time, she applied for a highly coveted Marie Curie Fellowship — but was unsuccessful, for once. Yet through Swiss project partners, she learned about the newly created SNSF Swiss Postdoctoral Fellowships as an alternative to the EU funding program. With a success rate of only 9 percent, this was another highly competitive fellowship. This time she succeeded with her research project on the role of the Southern Ocean in the carbon cycle.

Centre of paleoclimatology

Chuxian Li chose the University of Bern and the Oeschger Centre as the location for her two-year project because she has found "the right environment" here. That is to say: For one thing, the necessary infrastructure is available to measure mercury isotopes, which again play a central role in her new project. Plus there is great expertise in paleoclimatology and the analysis of natural climate archives. But also important to Chuxian Li's project is her collaboration with the British Antarctic Survey. This polar research program has provided her with samples from peat soils from six locations around Antarctica — from the Kerguelen Islands to Tierra del Fuego and Macquarie Island.

These areas are located in the westerly wind zone of the southern hemisphere — a look into their past climates is central for Li's research. And: There are peat bogs there, a particularly interesting climate archive if you are interested in mercury isotopes. That's because these enter the soil mainly via rain, and in turn, the amount of rain is directly related to wind strength. In other words, mercury isotopes are a so-called proxy for rain and thus for wind. "I will deliver the first quantitative reconstruction of how the dynamics of westerly winds in the Southern Hemisphere have changed over the past 17,000 years," Li promises. This information could help explain under which conditions the Southern Ocean functions as a CO₂ sink and when it functions as a source of CO₂. After all, the strength of the wind is the decisive factor for ocean circulation and the carbon cycle.

What's unique about Li's approach is that she wants to prove the link between rainfall and wind strength using measured data — the concentration of mercury isotopes in peat cores. "So far, these are theoretical considerations," she explains, "it won't be easy to prove them empirically." Hasn't anyone done that yet? "No, that's just the thing!" bursts out Chuxian Li. "This is a brand new idea, which is why I'm fighting so hard for this project," she beams.

(January 2023)