The response of trees to climate is crucial for the health assessment and protection of forests in alpine regions. Based on samples of Pinus tabuliformis and Abies fargesii, two typical evergreen coniferous species with distinct elevation differences in the vertical vegetation zones of the Qinling Mountains, we have developed two tree-ring width chronologies for the southern slope of the central Qinling Mountains in central China. The correlation analysis results showed that the radial growth of P. tabuliformis and A. fargesii responded to different climatic factors. Water stress caused by temperature in May of the current year was the main limiting factor for radial growth of P. tabuliformis, while precipitation in September of the previous year and the current year had a negative impact on A. fargesii, with lag effects of temperature and precipitation during the previous growing season. Spatial correlation and comparative analysis indicated that the P. tabuliformis chronology responded to extreme dry and wet events on a regional scale. Interannual and multidecadal periodic signals recorded by tree rings suggested that the hydrological and climatic changes on the southern slope of the central Qinling Mountains were teleconnected with the Pacific and Atlantic Oceans, including El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO). Our results provide new evidence for a hydroclimatical response study inferred from tree rings on the southern slope of the central Qinling Mountains.

Palaeoclimate proxies reveal a significant precessional impact on the low-latitude hydrological cycle. Classical theory suggests that precession modulates the inter-hemisphere summer insolation difference and hence controls the meridional displacement of the Intertropical Convergence Zone (ITCZ). Accordingly, low-latitude precipitation variations are expected to be in phase (for the Northern Hemisphere) or anti-phase (for the Southern Hemisphere) with the Northern Hemisphere summer insolation. However, increasing numbers of proxies, particularly those that are absolutely dated, reveal that variations in terrestrial precipitation at different low latitudes follow distinct precession rhythms that are very often out of phase with hemispheric summer insolation. The mechanism underlying such spatial–temporal complexity remains elusive. In this study, we performed theoretical analysis, climate simulations, and synthesis of geological records to hypothesise that the low-latitude hydrological cycle is paced by shifting perihelion rather than by the hemispheric summer insolation. More specifically, precession of the Earth’s rotation axis shifts the season and latitude of perihelion. Here, the latitude of perihelion is introduced as the latitude of Earth's subsolar point during perihelion, which is the location where the most intense solar radiation is concentrated. At the time of perihelion, intense solar radiation heats the land faster than the ocean due to differing thermal inertia. This thermodynamically moves the tropical convection from the ocean to the land, contributing to enhancing the terrestrial precipitation around the perihelion latitude. As the precessional phase changes, perihelion moves toward different latitudes, causing asynchronous maximums in terrestrial precipitation at different latitudes. Perihelion can occur in any season; therefore, the insolation in individual seasons is equally important in shaping the orbital-scale climate changes at low latitudes. This offers new insight into the Milankovitch theory, which highlights summer insolation's role in shaping orbital-scale climate change.

The Qinling Mountains in central China are rich in polymetallic mineralizations (e.g., Pb-Zn-Au deposits), and historic mining has resulted in large amounts of heavy metals being released into the environment. Thus, it is important to evaluate the ecological risk triggered by historic mining at this location. In this work, a gold mine was investigated as a case study to better understand the health risks present in the Qinling Mountains. To address this issue, a total of 84 soil samples and 23 surface water samples were collected from the gold mining district. Major and trace elements in soils, coupled with the pH and SO₄⁻² contents in water samples, were analyzed. The multivariate statistical analysis shows that human activities were found to have a significant impact on the levels of heavy metals (e.g., As, Hg, and Cd), pH, and SO₄⁻² in the soil within the study area, and the coefficient of variation for all indicators falls within a medium to high range (0.20–2.73). The maximum concentration of Cd can reach as high as 3005 mg·kg⁻¹. The spatial distribution of Cd and its isotope signatures indicate that sedimentation ponds and slag piles are the primary sources of high pollution within the study area, with heavy metal concentrations decreasing gradually as they disperse into the surrounding cultivated areas. The present study confirms that Cd and its isotopes can be directly used to track heavy metal sources over a large area (0.8 km²), and the conclusions drawn could be valuable for future restoration and management efforts. Simultaneously, this approach could offer a novel framework for the management of heavy metal contamination in soils at other metal mining sites.

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‰.