Katsuko Saruhashi, marine geochemist who measured CO2 in the oceans and showed how radioactivity spread from nuclear testing

Katsuko Saruhashi, linocut print, 9.25" x 12.5" by Ele Willoughby, 2025

This is my hand-carved and hand printed linocut portrait of Japanese geochemist Katsuko Saruhashi (1920-2007) who created tools that allowed her to make the first measurements of CO2 in seawater, raised the alarm about nuclear fallout, tracing it in the oceans, and researched peaceful uses of nuclear power. A supporter of women in science, she established the Society of Japanese Women Scientists and the Saruhashi Prize for Japanese women researchers for excellence in science and mentoring women scientists. Each print is 9.25” x 12.5” on Japanese kozo, or mulberry paper. I made this print for the #printerSolstice2425 prompt carbon.

Born in 1920, the story goes that her interest was sparked in science watching raindrops in primary school, wondering about the source of rain. Her parents believed in education, but she had to make a case to leave a secure insurance job at 21 to study chemistry. Her family witnessed how women struggled to support themselves without husbands or fathers in wartime. So her mother thought science might be a good way to ensure financial independence. She studied chemistry at the Imperial Women's College of Science (now Toho University). After completing her undergrad degree in 1943 she worked at the Geochemical Laboratory at the Meteorological Research Institute (now the Japan Meteorological Agency) with her mentor, marine chemist and lab director Miyake Yasuo, who had a strict policy against gender discrimination. She developed the first tool to measure CO2 in the oceans using pH and chlorinity, called Saruhashi's Table. She enrolled in the PhD program at the renowned University of Tokyo in 1957, where she was the first woman to earn a science doctorate. Her dissertation was on "The Behaviour of Carbonic Matter in Natural Water". With Miyake, she showed that oxidation of organic material increased CO2 in the ocean; prior to this, oceanic CO2 levels were attributed to dissolved calcium carbonate (for instance from in sea shells) and that global warming could be mitigated by seawater's supposed ability to absorb CO2. She not only showed this was untenable, she found the Pacific Ocean emits more CO2 than it absorbs! This has dire consequences for climate change. 

With Teruko Kanzawa from 1973 to 1978, she recorded the pH of every rainfall, documenting acid rain over the five-year period at the Meteorological Research Institute in Tokyo. 

 

After WW2 the US persisted in testing nuclear weapons at the Bikini Atoll, roughly 4000 km southwest of Japan, and in 1954 several Japanese fishermen became ill after trawling downwind of the testing site. The Japanese government asked the Geochemical Laboratory to investigate. Measuring small concentrations of radioactive elements dispersed in the ocean is quite a difficult technical challenge. Saruhashi and her colleagues used radionuclides to trace ocean circulation about found dispersion was uneven, circulation went clockwise and radiation-contaminated waters went northeast towards Japan, arriving in just 18 months and at much higher concentrations than on the US Pacific coast. Continued testing could contaminate the entire ocean, even if done in such an isolated place. The U.S. Atomic Energy Force was skeptical and sponsored a lab swap, bringing Saruhashi to the Scripps Institute of Oceanography at UCSD so her methods could be compared with those of US oceanographer Theodore Folsom. The two methods gave very similar results and the precision of her methods were undeniable. Her research provided critical evidence to support the end of above ground nuclear testing during the cold war. 

After her positive experience working with Miyake, Saruhashi noticed how differently she was treated as a woman researcher at the University of Tokyo, where she had to prove her abilities, and at Scripps, where her US counterpart Folsom told her not to bother coming in every day and assigned her a wooden hut to work in. Saruhashi believed firmly science and society were linked and that scientists bear social responsibility and should be engaged with the public. She was the first woman elected to the Science Council of Japan, to win Japan’s Miyake Prize for geochemistry. She won the Avon Special Prize for Women for promoting the peaceful use of nuclear power, and the Tanaka Prize from the Society of Sea Water Sciences. She said, “I would like to see the day when women can contribute to science and technology on an equal footing with men.”  She founded the Society of Japanese Women Scientists to recognize women in science and create a venue for discussion of issues faced by women in science as early as 1958. In 1981, she established the yearly Saruhashi Prize, awarded to a woman scientist who serves as a role model for younger women scientists.

She made a lasting impact on our understanding of human impacts on the ocean, climate, and radioactive contamination, blazed a trail for women scientists in Japan and helped foster the next generation of researchers. 

References

Katsuko Saruhashi, Wikipedia, accessed January 2025

Mast, Laura, Meet Katsuko Saruhashi, a resilient geochemist, who detected nuclear fallout in the Pacific, Massive Science, March 22, 2019