Multi‐Timescale Variations of δ18O‐δ13C in Stalagmites: Insights Into Isotopic Disequilibrium and Human Activities

Abstract The reasons for covariations of speleothem δ 13 C and δ 18 O remain controversial, primarily due to the limited high‐resolution stalagmite records that can be compared with meteorological data. This study presents δ 13 C and δ 18 O records of two coeval, annually laminated stalagmites (TS9701 and TS9501) spanning the past ∼2000 years from Shihua cave, Beijing, northern China. The low correlation between stalagmite TS9701 records, with annual resolution, and local annual precipitation as well as mean annual temperature on interannual to decadal scales indicates that the positive covariations of δ 18 O and δ 13 C in TS9701 are partly attributed to kinetic isotope effects caused by rapid CO 2 degassing. Isotopic disequilibrium between HCO 3 − (aq) and drip water, induced by prior calcite precipitation on cave ceiling and stalactite surface, is another potential contributing factor. δ 18 O and δ 13 C exhibits distinct patterns on multidecadal to millennial timescales. δ 18 O records show notable centennial variability, aligning with El Niño‐Southern Oscillation cycles. In contrast, δ 13 C profiles reveal a decreasing trend during the first ∼750 years, followed by an increasing trend. Prior to 1588 AD, variations in δ 13 C broadly correspond to changes in warm season temperature and/or moisture on centennial scale. Both δ 13 C records show an abrupt enrichment between 1588 and 1654 AD. Historical documents indicate that this anomaly is likely attributed to coal mining and resultant deforestation around Shihua cave during late‐Ming and early‐Qing Dynasties. In summary, while isotopic disequilibrium can cause high‐frequency covariations of speleothem δ 18 O and δ 13 C, it does not erase the imprints of climate changes and human activities on multidecadal to millennial timescales.