Speleothem δ¹³C in monsoonal China differs from speleothem δ¹⁸O, which is widely used as a climatic proxy for several complex control reasons. Nevertheless, δ¹³C records have the potential to reveal the implications of hydroclimatic changes. This study reports a speleothem δ¹³C record from Didonghe (DDH) Cave in central China spanning 34 to 13 kyr BP. After we investigated the factors that influence speleothem δ¹³C, we found that the δ¹³C record showed that DDH Cave can prompt directional shifts via local hydroclimatic changes, such as in vegetation types, biomass, and rock–water interaction processes, suggesting that δ¹³C is mainly controlled by the local hydroclimate. Ensemble empirical mode decomposition (EEMD) results revealed a coupling relationship between δ¹⁸O and δ¹³C on multiple timescales, which suggested that changes in precipitation caused by large-scale monsoonal circulation are controlled by regional hydrological conditions to a great extent. However, the hydrological conditions of the cave were relatively mild and humid during the last glacial maximum (LGM), which revealed the impact of evaporation on changes in the region’s hydrological conditions. We also found that the δ¹⁸O and δ¹³C profiles decoupled when δ¹³C changed with a shift in the location of the westerly during HS1. The δ¹³C record correlates well with other paleoclimate records, suggesting that regional hydrological conditions are also modulated by the Earth’s internal and external driving factors.

The carbon isotopic composition of dissolved organic carbon (δ¹³C_DOC) in speleothems, based on high-precision U-Th ages, has great potential to reconstruct past ecology, microbial activity, and carbon cycling. Identifying the reliability of the pretreatment and measurement of speleothem δ¹³C_DOC is therefore essential to putting it into practice. Actually, we have previously verified the reliability of the method for speleothem δ¹³C_DOC measurements. However, it was only based on the final δ¹³C_DOC values of homogeneous speleothem powder and is unable to evaluate the effects of different experimental conditions and the impacts of adding acid on δ¹³C_DOC if using speleothem as the study samples. In this study, we used an organic reagent (potassium sorbate) as the study sample and designed a conditional experiment that simulates the protocols for speleothem δ¹³C_DOC analysis and presented the resulting data to inspect the effects of the experimental processes on the analysis of δ¹³C_DOC. The results show that the standard deviation of duplicate samples is 0.1‰, which is close to that of the previous work for organic reagents and water samples, and the results were not affected by different experimental conditions and operation steps (such as adding orthophosphoric acid, digestion time, and storage duration of resulting CO₂ in storage vessels), suggesting that this method is robust to detect the speleothem δ¹³C_DOC. Considering the range and standard deviation of results, we proposed that the δ¹³C_DOC record could be used in various studies when the amplitudes of the δ¹³C_DOC record are larger than 0.1‰, especially greater than 0.4‰.

The complexity of processes affecting soil organic carbon (SOC) turnover on spatio-temporal scales often hinders the extrapolation of results from specific sites to larger scales. This study presents Holocene speleothem U-Th ages paired with 14C ages of carbonate and dissolved organic carbon (DOC) through three caves located on a north-south transect through China. The deviations of speleothem 14CDOCages from the U-Th ages show clearly spatial variability, and they are positively correlated with mean ages of modern SOC and soil turnover time, suggesting that deviations can be used to infer the SOC turnover. We further demonstrate that slow SOC turnover (large deviation) was associated with weak monsoon (low temperature/less precipitation) on temporal scales. Our findings reveal that climate dominates the speleothem 14CDOCages and SOC turnover. As global warming likely will intensify, the accelerated turnover of SOC, particularly at higher latitude areas, may partially offset the existing soil carbon stock.