『Abstract
　The Duman River and the hot springs and streams of Mt. Baekdu were sampled and analyzed for their major elements, ⁸⁷Sr/⁸⁶Sr, δD, δ¹⁸O, and δ¹³C. The Duman River drains an extensive volcanic plateau in northeast Asia and Mt. Baekdu is a volcanic cone on the plateau, and their fluvial geochemistry reflects weathering of volcanic rock. Two different volcanic end-members could be distinguished - basalt and trachyte. Weathering of trachytic rock is characterized by lower Ca/TZ⁺ and higher ⁸⁷Sr/⁸⁶Sr (＞0.7082), while that of basaltic rock contributes higher Ca/TZ⁺ and lower ⁸⁷Sr/⁸⁶Sr (＜0.7050). Carbon isotope analyses (δ¹³C of dissolved inorganic carbon, dissolved organic carbon and particulate organic carbon) along with chemical variations of major elements in the main channel suggest a transition from volcanic rock weathering in the upper reach to carbonate weathering in the lower reach. The ⁸⁷Sr/⁸⁶Sr ratio was useful in discerning minor input from granitoid rocks in the lower reach. According to the δD - δ¹⁸O data, the source of the river water in August is mostly precipitation supplied from the East Sea/Japan Sea related to the summer monsoon of East Asia. The natural CO2 uptake rate is estimated to be 22.2〜27.8×10⁴ mol・km^-2・yr^-1. This is on the lower end of other basaltic regions of the world and is due to lower temperature and runoff and to lack of glaciation. The hot spring samples of Mt. Baekdu have high TDS (total dissolved solids, 381〜1431 mg/L) and are of Na-HCO3 type. Geothermometric calculations and δD - δ¹⁸O data indicate that meteoric water infiltrates into the geothermal field but emerges at the surface before attaining equilibrium with the host rock. The hot spring samples affect the chemistry of nearby freshwater streams but are chemically distinct from the Duman River.

Keywords: Chemical weathering; CO2; ⁸⁷Sr/⁸⁶Sr; δ¹³C; δ¹⁸O』

1. Introduction
2. Study area
3. Methods
4. Results and discussion
　4.1. Major element chemistry
　4.2. Sr isotope ratio
　4.3. δ¹³C of DOC, POC and DIC
　4.4. δD and δ¹⁸O
　4.5. Geochemical evolution in the main channel
　4.6. Geothermometry of Mt. Baekdu springs
　4.7. Calculation of silicate weathering rate and CO2 uptake rate
　　4.7.1. Forward calculation
　　4.7.2. Weathering and CO2 uptake rates
5. Conclusion
Acknowledgements
References