Groundwater Diffuse Recharge and its Response to Climate Changes inSemi-Arid Northwestern China

Understanding the processes and rates of groundwater recharge in arid and semi-arid areas is crucial for utilizing and managing groundwater resources sustainably. We obtained three chloride profiles of the unsaturated-zone in the desert/loess transition zone of northwestern China and reconstructed the groundwater recharge variations over the last 11, 21, and 37 years, respectively, using the generalized chloride mass balance (GCMB) method. The average recharge rates were 43.7, 43.5, and 45.1 mm yr-1, respectively, which are similar to those evaluated by the chloride mass balance (CMB) or GCMB methods in other semi-arid regions. The results indicate that the annual recharge rates were not in complete linear proportion to the corresponding annual precipitations, although both exhibited descending tendencies on the whole. Comparisons between the daily precipitation aggregate at different intensity and recharge rates reveal that the occurrence of relatively heavy daily precipitation per year may contribute to such nonlinearity between annual precipitation and recharge. The possible influences of vegetation cover alterations following precipitation change cannot be excluded as well. The approximately negative correlation between the average annual recharge and temperature suggests that changes in temperature have had significant influences on recharge.</p

Stable isotope composition alteration produced by the aragonite-to-calcite transformation in speleothems and implications for paleoclimate reconstructions

Aragonite, a mineralogical constituent of speleothems in cave environments, is unstable and susceptible to inversion to calcite, a diagenetic process that involves changes in the mineralogy, texture and geochemistry of speleothems. However, the exact alterations of stable isotope compositions during such diagenesis have not been fully investigated. In this study, two aragonite stalagmites (SN3 and SN15) from the Shennong Cave, southeast China, were found partially inverted to calcite, as determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses, and thin-section inspections under microscope. The fiber relics and textural ghosts of aragonite preserved in coarse and equant mosaic calcite crystals clearly indicate that the calcite in these two stalagmites were inverted from aragonite. The stable isotope compositions (delta C-13 and delta O-18, given in per mil versus VPDB standard) of primary aragonite and secondary calcite were analyzed and compared, along both growth layers and growth axes. The results show that, along growth layers, differences of delta C-13 values between aragonite and calcite are negligible (0.1 parts per thousand-0.2%.), whereas differences of delta O-18 values between aragonite and calcite are significant (0.63 parts per thousand-0.87%0). Comparisons along growth axes show similar results: i.e., differences of delta 13C values are negligible (0.06% +/- 0.22%.) whereas differences of delta O-18 values are significant (0.85 parts per thousand +/- 0.29%.). Most likely, the aragonite in SN3 and SN15 were internally inverted by interactions of trace calcite crystallites and pore water within intercrystalline pore spaces, by a dissolution-reprecipitation process occurring in trapped pore water. In the case of the inversion of aragonite to calcite in speleothems, such as that observed in SN3 and SN15, the delta 13C values could be used in paleoclimate and paleoenvironment reconstructions because they are inherited from those of primary aragonite. Although the delta O-18 values might be cross-calibrated to those of primary aragonite if the aragonite-calcite fractionation offset is known (e.g., 0.85 parts per thousand +/- 0.29%0 in this study), however, the delta O-18 values of secondary calcite should be used with caution in such reconstructions as the delta O-18 offset value is not consistently invariable.</p

Dentoalveolar paleopathology of the early modern humans from Zhirendong,South China

The fragmentary early Late Pleistocene, early modern human remains from Zhirendong, south China, present a suite of dentoalveolar pathologies and anomalies. The lesions include lower molar buccal alveolar resorption (Zhiren 1), massive dental caries in a mandibular molar associated with hypercementosis (Zhiren 2), and bilateral mesial premolar (P3) periapical lesions (granulomata with a probable left abscess) (Zhiren 3). The Zhiren 3 periapical lesions, given their bilaterality and the non-pathological incisor and canine alveoli, suggest dens evaginatus, although absence of the Zhiren 3 dentition prevents full evaluation of this diagnosis. These periodontal abnormalities join a number of similar lesions in Pleistocene humans, of varying severity. The carious lesion is noteworthy, given the rarity of them in the Pleistocene human fossil record. In addition, Zhiren 3 exhibits unilateral P3 rotation and bilateral I1 rotation (winging)

Trace-element variations in an annually layered stalagmite as recorders of climatic changes and anthropogenic pollution in Central China

We analyzed variations in the Sr/Ca, Ba/Ca, REE/Ca (REE: rare earth element), Zn/Ca, and Pb/Ca ratios preserved in an annually layered stalagmite, XL21, from central China. The stalagmite record spans the 95 year period AD 1914&ndash;2008. The Sr/Ca and Ba/Ca ratios have a significant positive correlation with the stalagmite&#39;s growth rate, suggesting that they were primarily controlled by growth-rate variations. Variations in REE/Ca ratios are consistent with local temperature changes, suggesting temperature influenced REE concentrations in the stalagmite over decadal to annual timescales. Higher temperature in this humid area can increase vegetation cover, microbial activity, and organic decomposition in the soil, resulting in enhanced pCO2, organic matter concentration and reduced pH, and consequently increased REE mobilization from the overlying soil layer and host rock. Higher temperatures may also increase the natural Zn mobilization from the overlying soil mediated by organic matter and consequently may have led to increased Zn retention in XL21. An increasing trend is seen in the Pb/Ca ratios from XL21 since 1985, which is consistent with increased lead production in this area, and indicates an increase in mine-derived lead pollution in the local environment over the past 30 years.</p

Quantitative temperature reconstruction based on growth rate of annually-layered stalagmite: a case study from central China

We used the annual growth rate of a stalagmite (XL21) collected from Xianglong Cave, central China, to quantitatively reconstruct regional terrestrial temperature changes over the last 95 years (1912-2006 AD). Based on a significant positive correlation between the growth rate and the observed temperature, a transfer function was designed, and the temperature from the previous September to May (P-9-5) was reconstructed, with an explained variance of 43.5%. Our results show an increasing trend in temperature during the last century, and especially over the last 30 years. The temperature variability from central China recorded here bears a striking similarity to that in the Northern Hemisphere, and also to global trends. However, the cooling between the 1980s and the early 1990s seen in the stalagmite record, which interrupted the warming trend that began in the 1960s, is not observed in the mean conditions found in China, the Northern Hemisphere, neither globally. This methodology for reconstructing historical temperature from stalagmite growth rates overcomes the limitation of the short meteorological observation period and supports the potential of stalagmite lamina climatology.</p

Dentoalveolar paleopathology of the early modern humans from Zhirendong,South China

The fragmentary early Late Pleistocene, early modern human remains from Zhirendong, south China, present a suite of dentoalveolar pathologies and anomalies. The lesions include lower molar buccal alveolar resorption (Zhiren 1), massive dental caries in a mandibular molar associated with hypercementosis (Zhiren 2), and bilateral mesial premolar (P3) periapical lesions (granulomata with a probable left abscess) (Zhiren 3). The Zhiren 3 periapical lesions, given their bilaterality and the non-pathological incisor and canine alveoli, suggest dens evaginatus, although absence of the Zhiren 3 dentition prevents full evaluation of this diagnosis. These periodontal abnormalities join a number of similar lesions in Pleistocene humans, of varying severity. The carious lesion is noteworthy, given the rarity of them in the Pleistocene human fossil record. In addition, Zhiren 3 exhibits unilateral P3 rotation and bilateral I1 rotation (winging).</p

Climate significance of speleothem d18O from central China on decadaltimescale

Speleothem-based oxygen isotopic sequences have been widely used to reveal regional climatic changes worldwide. However, the climatic significance of speleothem d18O variations in monsoonal China on decadal- to annual timescales remains in debate, which limits its application to paleoclimate reconstruction in the world&rsquo;s largest country by population. In this study, we analyzed a seasonally resolved d18O record of an annually layered stalagmite, XL21 whose variability covers a period of 98 years (1912&ndash;2009 AD), from Xianglong Cave, central China. The annual d18O trend shows an inverse relationship with local monsoon precipitation, suggesting speleothem d18O variations in this area can reflect monsoon precipitation at least on decadal timescale. Changes in moisture sources and transport pathways have little effect on the d18O variations in speleothems/monsoon precipitation on decadal timescale, which may be ascribed to similar distances from this region to the two main moisture sources, the Bay of Bengal and West Pacific. There is an anti-phase relationship between speleothem d18O records from central China and India during the last 98 years, which indicates the relationship between Indian monsoon intensity and speleothem d18O from central China on short timescales requires further investigation.</p

Centennial-to decadal-scale monsoon precipitation variability in the semi-humid region, northern China during the last 1860 years: Records from stalagmites in Huangye Cave

We developed a composite oxygen isotopic record of cave calcite for the last 1860 years based on three stalagmites from the Huangye Cave in eastern Gansu Province, northern China. The delta(18)O values reflect monsoon precipitation changes, with lower d18O values representing higher precipitation and vice versa. Three intervals of high precipitation were identified at AD 138-450, AD 730-1200, and AD 1860-1960. Two intervals of low precipitation occurred at AD 1320-1410 and AD 1530-1860. The reconstructed monsoon precipitation variations correlate well with other records further east in the eastern Yellow River Basin, suggesting synchronous precipitation changes during the late Holocene in the semi-humid region of northern China on decadal to centennial scales. Peak periods of warfare in dynastic transition times, such as at AD 391-420, AD 601-630, AD 1111-1140, AD 1351-1380, and AD 1621-1650, correspond to sharp declines in precipitation or temperature in semi-humid northern China, indicating a strong connection between climatic and societal changes. Our study suggests that climatic deterioration in semi-humid northern China has played an important role in Chinese societal evolution.</p

New 400e320 ka Gigantopithecus blacki remains from Hejiang Cave,Chongzuo City, Guangxi, South China

Gigantopithecus blacki is a typical member of the StegodoneAiluropoda faunal complex (sensu lato) that inhabited southern China or, more broadly, mainland Southeast Asia during the Early and Middle Pleistocene. Current evidence indicates that the giant ape became extinct during the Middle Pleistocene. Recently, new remains of G blacki and associated mammalian fossils have been unearthed from a karst cave site, Hejiang Cave, in Chongzuo City, Guangxi, South China. The age of the Gigantopithecus-bearing depositional unit is estimated to be 400e320 ka using 230The234U disequilibrium U-series dating of flowstone samples bracketing the deposits. These finds document the latest occurrence of Gigantopithecus and provide potential insights regarding its extinction. Comparisons of dental dimensions between the Hejiang G. blacki remains, more than four hundred isolated teeth from Early Pleistocene localities, and over ninety isolated teeth from local drugstores show that the Hejiang teeth are slightly larger in their buccolingual dimensions. In addition, the crowns of the three unerupted upper premolars differ from those of all of the other Gigantopithecus material in having more complex crenulations. The differences in dental dimensions and morphology are possibly reflective of dietary responses to environmental changes that eventually led to the extinction of Gigantopithecus.</p