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Reika Yokochi

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Reika Yokochi (in the center) and fellow scientists extracting gases from a water production well in the Negev Desert.

Reika Yokochi (born 1975 in Saga, Kyushu Prefecture, Japan) is a Japanese geochemist working on the origin and geological behavior of volatile elements. She currently holds the position of Research Professor in the Department of the Geophysical Sciences at the University of Chicago.[1] Yokochi leads a laboratory specializing in the purification and analysis of noble gases for dating and tracing water circulation within Earth's crust.[1][2]

Education and early career

Yokochi completed her doctoral studies in earth sciences at National Polytechnic Institute of Lorraine (French: L'Institut National Polytechnique de Lorraine) in 2005, supervised by Bernard Marty. Her PhD thesis focused on understanding the origin of volatile elements in Earth. She identified the presence of noble gases of solar origin in Earth's deep mantle. She also worked out the contribution of 244Pu-decay (t1/2=81 Myr) to fissiogenic 136Xe* in the deep Earth, suggesting a protracted loss of volatiles from Earth's mantle.[3] Between 2005 and 2008, she was a postdoctoral researcher with Neil C. Sturchio at the University of Illinois Chicago, after which she joined the University of Chicago as researcher in 2008.[1]

Research activities

Yokochi's research focuses on noble gas geochemistry. She uses noble gases radionuclides, notably Krypton-81 (81Kr), to study the age and circulation of groundwater in major aquifers worldwide, including the Nubian Sandstone Aquifer,[4][5] Floridan Aquifer,[6] and the geothermal waters of Yellowstone.[7]

81Kr Groundwater Dating Method Explained: Krypton-81 (81Kr) is generated in the atmosphere through cosmic rays interacting with stable krypton isotopes. This isotope, along with stable krypton, gets dissolved in rainwater and enters groundwater at recharge sites. As the groundwater moves away from these sites, the 81Kr gradually decays, reducing its ratio to stable krypton. By analyzing groundwater samples from wells, scientists can measure the 81Kr/krypton ratio. Lower ratios indicate that a longer period has passed since the water was recharged.

Krypton-81 dating is a scientific method used to determine the age of groundwater. This rare isotope is produced by cosmic rays in the atmosphere and then dissolves into rainwater, eventually seeping into groundwater. With a half-life of 230,000 years, 81Kr can be used for dating groundwater up to a million years old. The overall abundance of krypton in the atmosphere is only about 1.10 parts per million by volume (ppmv), and within this, the fraction of 81Kr is extremely small, about 5 × 10−13. Extracting krypton from groundwater is challenging, requiring processing of large volumes of water.[8] The isotopic abundance of 81Kr is measured using Atom Trap Trace Analysis (ATTA). Despite these technical challenges, 81Kr dating is a valuable tool for understanding groundwater history as krypton behaves as an inert tracer during groundwater transport.[9] In a study of the Nubian Sandstone Aquifer in Israel's Negev Desert, Yokochi and colleagues utilized radiokrypton (81Kr) to date groundwater, discovering two major water recharge events.[10] The first, about 38,000 years ago, originated from the Mediterranean, and the second, around 361,000 years ago, from the tropical Atlantic. These events, coinciding with periods of low orbital eccentricity, reveal the sensitivity of moisture transport to orbital forcing. The study highlights groundwater's potential as a record of ancient precipitation and long-term subsurface water storage.

Application of 81Kr to the Floridan Aquifer revealed freshwater recharge from the Last Glacial Period.[6] Additionally, it detected fossil seawater predating the Last Glacial Maximum, indicating slow seawater movement and a limited but significant exchange of solutes with the ocean, contributing to the aquifer's dolomitization.

Yokochi also contributed to the analysis of gases in samples returned from the Ryugu asteroid by JAXA's Hayabusa2 mission.[11][12]

Awards and recognition

Yokochi received the Young Scientist Award from the Geochemistry Research Association of Japan in 2012; the same year, she was also named a NASA Planetary Science Early Career Fellow.[13]

Personal life

Reika Yokochi is married to Nicolas Dauphas, a fellow planetary scientist; the couple has two children.[citation needed]

References

  1. ^ a b c "Reika Yokochi". Department of the Geological Sciences, University of Chicago. Archived from the original on 2023-07-14. Retrieved 2023-12-25.
  2. ^ "Reika Yokochi". Google Scholar. Retrieved 2023-12-25.
  3. ^ Yokochi, Reika (2005-01-01). L' azote, le néon et le xénon dans le manteau : sources, processus et hétérogénéités (PhD thesis thesis) (in French). National Polytechnic Institute of Lorraine. Archived from the original on 2021-02-07. Retrieved 2023-12-25.
  4. ^ Spizzirri, John; Lerner, Louise (2019-07-29). "Krypton reveals ancient water beneath the Israeli desert". University of Chicago News. Archived from the original on 2023-07-02. Retrieved 2023-12-25.
  5. ^ Strongin, Ronni (2019-07-30). "Krypton Reveals Ancient Water Beneath the Negev". Americans for Ben-Gurion University. Retrieved 2023-12-25.
  6. ^ a b Mitchem, Savannah (2021-09-30). "Scientists use nuclear physics to probe Floridan Aquifer threatened by climate change". Argonne National Laboratory. Archived from the original on 2023-02-09. Retrieved 2023-12-25.
  7. ^ Yokochi, R.; Sturchio, N. C.; Purtschert, R.; Jiang, W.; Lu, Z. -T.; Mueller, P.; Yang, G. -M.; Kennedy, B. M.; Kharaka, Y. (2013-02-15). "Noble gas radionuclides in Yellowstone geothermal gas emissions: A reconnaissance". Chemical Geology. Frontiers in Gas Geochemistry. 339: 43–51. doi:10.1016/j.chemgeo.2012.09.037. ISSN 0009-2541.
  8. ^ Yokochi, Reika; Heraty, Linnea J.; Sturchio, Neil C. (2008). "Method for Purification of Krypton from Environmental Samples for Analysis of Radiokrypton Isotopes". Analytical Chemistry. 80 (22): 8688–8693. doi:10.1021/ac801804x.
  9. ^ Lu, Z.-T.; Schlosser, P.; Smethie, W.M.; Sturchio, N.C.; Fischer, T.P.; Kennedy, B.M.; Purtschert, R.; Severinghaus, J.P.; Solomon, D.K.; Tanhua, T.; Yokochi, R. (2014). "Tracer applications of noble gas radionuclides in the geosciences". Earth-Science Reviews. 138: 196–214.
  10. ^ Yokochi, R.; Ram, R.; Zappala, J.C.; Jiang, W.; Adar, E.; Bernier, R.; Burg, A.; Dayan, U.; Lu, Z.T.; Mueller, P.; Purtschert, R. (2019). "Radiokrypton unveils dual moisture sources of a deep desert aquifer". Proceedings of the National Academy of Sciences. 116 (33): 16222–16227.
  11. ^ Lerner, Louise (2022-06-09). "Scientists release first analysis of rocks plucked from speeding asteroid". University of Chicago News. Archived from the original on 2023-07-02. Retrieved 2023-12-25.
  12. ^ Okazaki, Ryuji; Marty, Bernard; Busemann, Henner; Hashizume, Ko; Gilmour, Jamie D.; Meshik, Alex; Yada, Toru; Kitajima, Fumio; Broadley, Michael W.; Byrne, David; Füri, Evelyn; Riebe, My E. I.; Krietsch, Daniela; Maden, Colin; Ishida, Akizumi (2023-02-24). "Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution". Science. 379 (6634). doi:10.1126/science.abo0431. ISSN 0036-8075. Archived from the original on 2023-05-21. Retrieved 2023-12-25.
  13. ^ "Reika Yokochi". University of Chicago. Archived from the original on 2022-04-18. Retrieved 2023-12-25.
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