Symposium Sessions
Day 1, June 10（Wed.） 15:30-15:48 Room A (5F 503)
- 1A-S2-1530
Revisiting “first generation" non-traditional stable isotope geochemistry in the Japanese Archipelago
(Univ. Tokyo)
oTakaaki Itai, Kohki Frusho, Haruto Nakayam
Stable isotope ratio analysis requires high-precision mass spectrometry and has become a fundamental tool for tracing elemental cycles in geochemistry. The development of multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) since the early 2000s enabled precise isotope measurements for many elements and led to the rapid expansion of “non-traditional stable isotope” geochemistry. Among these systems, silicon and magnesium isotopes were investigated relatively early and are now widely used as tracers of chemical weathering processes. However, despite the geological diversity of the Japanese Archipelago, their application to natural environments in Japan has remained limited. In this study, we measured δ³⁰Si and δ²⁶Mg in major Japanese rivers using MC-ICP-MS to constrain the sources and processes controlling river chemistry. The results show elevated δ³⁰Si values associated with paddy-field dominated catchments, suggesting biological uptake and recycling of dissolved silica. In contrast, riverine δ²⁶Mg values are significantly lower than typical silicate values and approach seawater compositions, indicating that conventional element-ratio approaches may not fully explain Mg sources in Japanese rivers.