Focusing on the water circulation on the Earth's surface, we investigate unique and imporatant climate archvies (ice core, speleothems) using oxygen and hydrogen stable isotopic ratios of water. We also conduct present-day field works and experiments to improve the interpretation of the climate proxies.

 

　Speleothems

-Paleocimate research using fluid inclusions in speleothems

We are conducting research focusing on the small amount of water (fluid inclusions) entrapped in stalactites. We have developed a high sensitivity method for measuring the isotope ratio of hydrogen and oxygen in fluid inclusions, and are conducting isotope analysis aiming to reconstruct the temperature in the past.

 

Relataed paper (open access) ⇒(Uemura et al, Geochimica et Cosmochimica Acta, 2016)

　Ice cores

Antarctic temperature reconstruction

We are developing a high accuracy temperature reconstruction method by analysis of ice core drilled at Antarctic Dome Fuji station.

By combining the two isotope ratio of water (oxygen and hydrogen), it is possible to estimate the temperature of the mositure-sourece ocean where the water vapor has been evaporated, in addition to the temperature of Antarctica.

◎Antarctic and mositure-source ocean temperatures over the past 720,000 years, and discussed thier relation with atmospheric CO2. Related paper (open access)⇒(Uemura et al., Nature Communications, 2018)。

 

 

　Climate Proxy

Dominant influence of the humidity on the ¹⁷O-excess in subtropical rainwater

Early studies suggest that the triple oxygen isotopes tracer, denoted as ¹⁷O-excess, reflects changes in the relative humidity in moisture source regions. Subsequent studies, however, suggest the importance of additional effects, such as snow formation and rain drop re-evaporation. We show a two-year record of the ¹⁷O-excess in precipitation on a maritime island (Okinawa) in the East Asian monsoon region. Interestingly, we demonstrate that the reconstructed relative humidity is quantitatively consistent with observations in the oceanic moisture source. These results suggest that the 17O-excess in precipitation in subtropical region is a unique quantitative tracer and proxy for hydrological and paleoclimate studies.

Related paper ⇒ ( Uechi and Uemura, Earth and Planetary Science Letters , 2019)