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This study monitored the isotopic compositions of precipitation in Guilin as well as the influence of El Niño–Southern Oscillation (ENSO) on the isotope ratios and water vapour sources from 2015 to 2016. The results indicate that the lower isotope values of precipitation from ocean water vapour source are affected by long transport distance and fractionation during summer and autumn. In contrast, the isotope values of winter and spring precipitation are affected by continental air masses and their evaporation sources yielding higher values. The intercepts of the local meteoric water line in Guilin are larger than those of the global meteoric water line, which is typical for subtropical monsoon climate. During the El Niño event, development of anomalous anticyclonic circulation enhances the northbound transport over the western Pacific and brings abundant water vapour to the southern part of China. During El Niño event prevailing period, precipitations exhibit a lower δ18O value and low d (deuterium excess) value, indicating that the 2015/2016 ENSO event had a significant effect on the precipitation distribution, precipitation amount, and isotope ratios in regional precipitation. [ABSTRACT FROM AUTHOR]

A field study was conducted in 2013 and 2014 where cotton was exposed to three N regimes: (1) the control without N application (low N); (2) 260 kg N ha−1 (medium N); (3) 520 kg N ha−1 (high N). Boll size, lint mass per boll, seed mass per boll, fiber length and strength were significantly decreased under N deprivation in the two years. The increased carbohydrate levels of LSCB (leaf subtending the cotton boll) led to decreased carbohydrate levels of fibers in the low N relative to the other N treatments. The low N embryos exhibited lower starch concentrations at 17 and 31 DPA (days post anthesis), and TNC (total nonstructural carbohydrate) concentrations at 17, 31, 45 and 52 DPA compared to medium N embryos. Starch levels in LSCB had negative associations with those in fibers at 17, 31 and 45 DPA, but positive associations with those in embryos at 24 and 45 DPA. Fibers expressed negative associations with embryos in glucose level at 24 and 38 DPA, and in TNC levels at 17 and 45 DPA. The study suggests that carbon assimilate levels in fibers and embryos could explain the difference in boll yield components and fiber quality. [ABSTRACT FROM AUTHOR]

High-resolution carbon and oxygen isotope records in stalagmites provide significant information for quantitative paleo-reconstructions of past temperature and precipitation. This paper describes results of isotopic analysis of dissolved inorganic carbon (DIC) in Panlong Cave water (from drips and shallow pools). Cave water was sampled monthly throughout 2012 and analyzed for δC composition. The values of δC in drip water were in the range of −10.42 to −16.07 ‰, while the values of δC in pool water were in the range of −1.88 to −6.94 ‰. Dissolved inorganic carbon isotope records showed a gradual stepwise negative excursion from January to August, and a gradual stepwise positive excursion from September to December. δC in cave water showed remarkable seasonal variations, which were negative excursion from 2 to 5 ‰ in rainy season than in dry season. A negative δC excursion in summer was not the result of vegetation types, which was contributed to enhance root respiration and decomposition of soil organic matter. A correlation between δC values of perennial drip water and pool water samples with air temperature and precipitation amount suggests that these negative excursions were caused by increasing air temperature during rainy season. Negative excursions in δC values of seasonal drip water were correlated with monthly precipitation, caused by the influx of soil organic matter into the cave. Hence, this paper provides an important framework and an empirical basis for reconstructing temperature from stalagmites and drip water in this region. [ABSTRACT FROM AUTHOR]

Abstract: Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ18O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∼29.5 to 14.7 ka and from ∼12.9 to 11.0 ka. At the time of the last glacial maximum (LGM), the East Asian summer monsoon weakened and then strengthened in response to changes in Northern Hemisphere insolation. As the ice sheets retreated the East Asian summer monsoon weakened, especially during Heinrich event H1, when atmospheric and oceanic teleconnections transferred the climatic changes around the North Atlantic to the monsoonal regions of Eastern Asia. A depositional hiatus between ∼14.7 and 12.9 ka leaves the deglacial record incomplete, but an abrupt shift in δ18O values at ∼11.5 ka marks the end of the Younger Dryas and the transition into the Holocene. Comparisons of the J1 record to other Chinese speleothem records indicate synchronous climatic changes throughout monsoonal China. Further comparisons to a speleothem record from western Asia (Socotra Island) and to Greenland ice cores support hemispherical-scale paleoclimatic change. Spectral and wavelet analyses reveal centennial- and decadal-scale periodicities that correspond to solar frequencies and to oscillations in atmospheric and oceanic circulation. [Copyright &y& Elsevier]

A 26-cm-long stalagmite (XY2) from Xinya Cave in northeastern Chongqing of China has been ICP-MS 230Th/U dated, showing a depositional hiatus at 2.3 cm depth from the top. The growth of the 2.3–26 cm interval determined by four dates was between 57 ka and 70 ka, with a linear growth rate of 0.023 mm/a. We have analyzed 190 samples for δ 18O and δ 13C, mostly in the 2.3–26 cm part. The δ 18O and δ 13C values between 57 ka and 70 ka reveal decadal-to-centennial climatic variability during the glacial interval of Marine Isotope Stage 4 (MIS4), exhibiting much higher resolution than that of the published Hulu and Dongge records during this interval. Speleothem δ 18O in eastern China, including our study area can be used as a proxy of summer monsoon strength, with lighter values pointing to stronger summer monsoon and higher precipitation, and vice versa. Two decreases in the δ 18O signature of XY2 record around 59.5 and 64.5 Ka are argued to correspond to the Dansgaard-Oeschger (D-O) events 17 and 18 respectively. The Heinrich event 6 (H6) can be identified in the record as a heavy δ 18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period. The XY2 δ 18O record shows very rapid change toward to the interstadial condition of the D-O event, but more gradual change toward to the cold stadial condition. This phenomenon found in the Greenland ice core records is rarely observed so clearly in previously published speleothem records. According to SPECMAP δ 18O record, the glacial maximum of MIS 4 was around 64.5 ka with the boundary of MIS 3/4 around 60 ka. Unlike the marine record, the speleothem record of XY2, China, exhibits much high frequency variations without an apparent glacial maximum during MIS 4. However, the timing of MIS 3/4 boundary seems to be around 60 ka when the H6 terminated, in agreement with the marine chronology. The growth period of sample XY2 during glacial times probably reflects a local karstic routing of water, rather than having climatic significance. [ABSTRACT FROM AUTHOR]

The time sequence of paleoclimatic changes from 245.2 to 147.9 ka B.P. has been established by high precision U-series dating by Thermal Ionization Mass Spectrometry and the analysis of the oxygen isotopes from a stalagmite of Shuinan Cave in Guilin. The oxygen isotope pattern is divided into three main intervals. The top part of the stalagmite (interval C) displays mainly relatively heavy oxygen isotopes, mostly −7 to −5‰VPDB, but at a depth of 86.5 cm below the top, there is a sharp change to values lighter than −8 ‰. This boundary, dated at 192.6 ±3.9 ka B.P. is correlated with the boundary between marine oxygen isotope stages 6 and 7. The underlying interval B has δ18O values consistently between −7.5 and −8.5‰ until 271 cm depth when there is a sharp rise in δ18O values towards values as heavy as −5‰. The upper position of this change is dated at 242.5±6.4 ka B.P. and is correlated with the boundary between marine isotope stages 7 and 8. Carbon isotope values lie between −8.5 and −11‰ and are not uniquely high or low in the three intervals, but also show rapid changes at the boundaries between intervals in the same sense as the shifts in δ18O. The pronounced shifts in δ18O are attributed to changes in the paleo-monsoon intensity which reflect major reorganizations of the climate system, but some regional characteristics are also present. The results are also consistent with previous studies of climate proxies from loess-palaesol sequences in northern China. These characteristics show that paleo-climate evolution since the late stage of the middle Pleistocene Epoch in the Guilin area not only follows the global characteristics, but also has the strong district or regional patterns. [ABSTRACT FROM AUTHOR]

Taking Huanglong Ravine and Kangding, Sichuan, and Xiage, Zhongdian, Yunnan, as examples, the authors summarize the hydrogeochemical and carbon stable isotopic features of the geothermal CO2-water-carbonate rock system and analyze the CO2 sources of the system. It was found that the hydrogeochemical and carbon stable isotopic features of such a system are different from those of shallow CO2-water-carbonate rock system, which is strongly influenced by biosphere. The former has higher CO2 partial pressure, and is rich in heavy carbon stable isotope. In addition, such a geothermal system is also different from that developed in igneous rock. The water in the latter system lacks Ca2+, and thus, there are few tufa deposits on ground surface, but it is rich in light carbon stable isotope. Further analysis shows that CO2 of the geothermal CO2-water-carbonate rock system is a mixture of metamorphic CO2 and magmatic CO2. [ABSTRACT FROM AUTHOR]

Abstract: Four 230Th-dated δ18O records in three stalagmites: one from Dragon Spring (stalagmite L12) and two from Golden Lion Caves (stalagmites JSD-01 and JSD-02) located in Libo County, southeast Guizhou, China, are presented. These records cover age ranges of 0.75–2ka (late Holocene), 9–9.6ka (early Holocene), 87.9–88.2ka and 93.8–95.2ka (late Pleistocene). They fit well with the published Dongge Cave record from the same area, where the climate has been much influenced by the East Asian Monsoon. The agreement reinforces the role of stalagmite δ18O as a proxy for regional precipitation or monsoon strength. On millennial or longer time scales, the δ18O record of Dongge Cave resembles those of Sanbao Cave in Hubei and Hulu Cave in Jiangsu of China. The matching of these records with the northern hemisphere solar-insolation variations points to the importance of insolation in affecting the East Asian Summer Monsoon strength on 103–104-yr scales. While the monsoon variations as depicted by these Chinese speleothem δ18O records show a strong coupling to insolation’s precession component (23-kyr period), other climate records of global significance extracted from oceanic and terrestrial deposits (e.g., deep-sea sediments, polar ice cores, cave deposits from non-monsoonal regions) do not. Although the latter records were thought to be also influenced by the large changes in global ice volume, they show variations modulated chiefly by insolation due to earth’s eccentricity change (100-kyr period). It is hypothesized that precession variations control the distribution of solar insolation between the northern and southern hemispheres, the ITCZ position and the modulation of low-latitude summer monsoon variability. Increasing rainfall and/or summer/winter precipitation ratio brought about by strong summer monsoons leads to δ18O depletion in stalagmites grown in monsoonal regions. One should use caution to compare speleothem δ18O records with other paleoclimate records reflecting Pleistocene ice ages on 104–105-yr timescales. [Copyright &y& Elsevier]