[ACC37-P06] The triple isotopic composition of oxygen for sulfate and nitrate in surface snow in a latudinal transect in East Antarcica
★招待講演
キーワード：安定同位体、三酸素同位体組成、硫酸、硝酸
The isotopic compositions of sulfate (SO42-) and nitrate (NO3-) reflect their sources and oxidation pathways. In particular, triple oxygen isotope compositions (Δ17O) are potential tool to reconstruct how the oxidants work in past and present atmosphere. Antarctica is an ideal place to investigate the past proxy, because the ice core preserves in past hundred thousands Earth’s history. However, recently we found the annual mean Δ17O values for atmospheric SO42- at coastal Antarctica is not matched with the Δ17O values preserved in the inland Antarctic ice core records. In addition, the lack of observation, spatial variations of Δ17O values are limitedly reported.
In order to test spatial variation of isotopic compositions, especially for the difference in Δ17O values between coastal site and inland site, here we present latitudinal variation of Δ17O value and conventional isotopic compositions (δ34S, δ15N, and δ18O) of SO42- and NO3- in surface snow in eastern Dronning Maud Land, East Antarctica. Snow samples were collected from the surface at low- and high-elevation sites during the 54th and 57 th Japanese Antarctic Research, respectively. Δ17O values of non-sea-salt (nss)-SO42- at the East Antarctica ranges from 2.2 to 3.3‰, and the Δ17O value of nss-SO42- for coastal site was lower than those for inland site. Thus, this result suggest that oxidizing chemistry for biogenic sulfur is different among coastal and inland sites, although small sulfur isotopic variations are observed and source of sulfur is biogenic and homogeneous. For the isotopic compositions of NO3-, considerably increasing values of δ15N of NO3- are observed from coastal to inland sites. The δ18O and Δ17O of NO3- values, on the other hand, decreases with increasing of δ15N values, indicating the secondary formation of NO3-. Thus, spatial variations of isotopic compositions of NO3- reflect the post-depositional processes on the East Antarctic snow.
In order to test spatial variation of isotopic compositions, especially for the difference in Δ17O values between coastal site and inland site, here we present latitudinal variation of Δ17O value and conventional isotopic compositions (δ34S, δ15N, and δ18O) of SO42- and NO3- in surface snow in eastern Dronning Maud Land, East Antarctica. Snow samples were collected from the surface at low- and high-elevation sites during the 54th and 57 th Japanese Antarctic Research, respectively. Δ17O values of non-sea-salt (nss)-SO42- at the East Antarctica ranges from 2.2 to 3.3‰, and the Δ17O value of nss-SO42- for coastal site was lower than those for inland site. Thus, this result suggest that oxidizing chemistry for biogenic sulfur is different among coastal and inland sites, although small sulfur isotopic variations are observed and source of sulfur is biogenic and homogeneous. For the isotopic compositions of NO3-, considerably increasing values of δ15N of NO3- are observed from coastal to inland sites. The δ18O and Δ17O of NO3- values, on the other hand, decreases with increasing of δ15N values, indicating the secondary formation of NO3-. Thus, spatial variations of isotopic compositions of NO3- reflect the post-depositional processes on the East Antarctic snow.