云南白水台内生钙华中 Mg/Ca、Sr/Ca、Ba/Ca 比值变化特征及其气候环境指示意义

Reconstructing high-resolution paleoclimate and environmental records is of great significance for deepening our understanding of the mechanisms driving global climate change and for predicting future climate trends. As a typical supergene sediment, travertine serves as an ideal geological archive for studying paleoclimate change at inter-annual to decadal scales due to its high sensitivity to climatic and environmental changes, rapid deposition rates, and widespread distribution. Previous real-time monitoring of trace elements by our research group in Baishuitai spring water over several years revealed that the concentrations of elements such as Mg, Sr, and Ba in the local spring water can reflect changes in local precipitation. However, it remains unclear whether variations in Mg, Sr, and Ba within the travertine itself can inherit the signals of these element variations observed in the spring water. This uncertainty limits the use of Mg, Sr, and Ba in travertine for paleoclimatic and environmental reconstruction. To further elucidate the climatic and environmental significance of Ca, Mg, Sr, Ba, and their ratios (Mg/Ca, Sr/Ca, Ba/Ca) in the endogenic travertine at Baishuitai, Yunnan Province, Southwest China, this study analyzed the concentrations of these elements and their ratios in both modern newly-formed travertine (May 2018 to October 2022, monthly resolution) and a modern travertine profile (from 2001 to 2016, semiannual resolution) from the Baishuitai area. The results show that: (1) Spring water is the primary source of Mg, Sr, and Ba in the Baishuitai travertine, while local precipitation and soil material carried by the overland flow serve as seasonal sources. (2) The peaks and troughs in the Mg/Ca, Sr/Ca, and Ba/Ca ratios of the modern newly-formed travertine correspond closely with those in the spring water during the same period, demonstrating strong consistency. This indicates that the variations in the Mg/Ca, Sr/Ca, and Ba/Ca ratios within the travertine primarily inherit the variations of these ratios in the spring water. Since changes in the Mg/Ca, Sr/Ca, and Ba/Ca ratios in the spring water mainly indicate variations in precipitation, the changes in these ratios in the travertine also primarily reflect precipitation fluctuations. Additionally, it was found that the distribution coefficients of Mg, Sr, and Ba between the spring water and modern newly-formed travertine show significant positive correlations with temperature (Mg: r = 0.45, p = 0.0007; Sr: r=0.42, p=0.002; Ba: r=0.43, p=0.0012), indicating that temperature is also an important factor influencing the Mg/Ca, Sr/Ca, and Ba/Ca ratios in the travertine. Furthermore, the Ba/Ca ratio in the travertine exhibits a significant positive correlation with the content of residue (r=0.3, p=0.041), suggesting that the Ba/Ca ratio is also affected by soil material input from the overland flow. (3) On an inter-annual scale, the Mg/Ca ratio in the white travertine layers shows a significant negative correlation with annual precipitation (r=-0.53, p=0.035), indicating that the Mg/Ca ratio in these white layers likely reflects changes in local precipitation. Concurrently, the Mg/Ca ratio in the dark travertine layers shows significant negative correlations with annual precipitation (Lijiang, no lag: r=-0.33, p=0.041; Lijiang, 1-year lag: r=-0.46, p=0.025; Shangri-La, 1-year lag: r=-0.42, p=0.045) and significant positive correlations with mean rainy season temperature (Lijiang: r=0.39, p=0.032; Shangri-La: r=0.42, p=0.033). This suggests that the Mg/Ca ratio in the dark layers likely reflects the combined influence of local precipitation and temperature. Additionally, the Sr/Ca ratio in the dark travertine layers shows a significant positive correlation with layer thickness (r=0.59, p=0.036), indicating that the Sr/Ca ratio may reflect changes in the travertine deposition rate. In summary, these findings provide an important scientific basis for utilizing geochemical indicators in travertine to reconstruct past high-resolution climate and environmental conditions.