リチウム同位体が水文変動の新指標として特定（Lithium isotopes identified as new indicator of hydrological change）

2026-03-16 中国科学院（CAS）

＜関連情報＞

• https://english.cas.cn/newsroom/research-news/202603/t20260316_1152731.shtml
• https://www.sciencedirect.com/science/article/abs/pii/S001670372600164X

水文学の変化を示す新たな指標としてのリチウム同位体 Lithium isotopes as a new indicator for change in hydrology

Yadan Hu, Fei Zhang, Chen Chen, Ying Xie, Li Deng, Xiangying Li, Xiaolong Zhang, Guang Bao, Jinzhao Liu, Zhangdong Jin
Geochimica et Cosmochimica Acta  Available online 12 March 2026
DOI:https://doi.org/10.1016/j.gca.2026.03.018

Abstract

Hydrology is a critical driving force that affects surface erosion and weathering, which regulates the long-term stability of Earth’s climate by removing atmospheric CO₂. However, reconstructing past hydroclimate remains a non-trivial challenge, due to the difficulty in isolating temperature effects. The negative correlation between globally compiled Li isotopes (δ⁷Li) and runoff suggests the potential of δ⁷Li as a hydrological proxy, yet confirming its validity still requires more field evidence. Here, we report the first weekly riverine δ⁷Li from a remote, rapidly eroding Muztag glacial basin (peak elevation of 7546 m) within the largest glacierized region of the mid-latitudes. Our results show remarkable seasonal changes in river δ⁷Li (up to ∼15‰), from 17.9‰ in the dry season to 2.5‰ in the wet season. The very low δ⁷Li in this tectonically active basin during the wet season contradicts the long-standing uplift-weathering hypothesis that intensified erosion increased incongruent continental weathering and higher riverine δ⁷Li. Instead, our findings unexpectedly exhibit a clear hydrological signal, with δ⁷Li showing a significant relationship with lake water levels but weak correlations with temperature. Changes in lake levels, together with riverine ⁸⁷Sr/⁸⁶Sr and Al/Si ratios, suggest that hydrologically driven variations in water–rock interaction time affect secondary mineral formation and seasonal riverine δ⁷Li. A further comparison of δ¹⁸O and δ⁷Li with temperature and lake level indicates that δ⁷Li provides a more suitable proxy for local hydrological changes than δ¹⁸O. Considering the debates regarding whether δ¹⁸O reflects changes in temperature or precipitation at regional or global scales, our findings have important implications for using δ⁷Li in lacustrine sedimentary records (e.g., authigenic carbonates) as a promising tool to decode past hydrologic state, thereby helping to isolate temperature effect.