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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]

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]

Abstract: Carbon isotopes in speleothems may serve as indicators of vegetative change, climatic conditions, and karst processes. In many recent studies of Chinese stalagmites, however, carbon isotopes have often been neglected or underutilized in interpreting paleoenvironments. Here, we present a continuous decadal-scale δ 13C record (819 measurements) of the mid- to late-Holocene from a precisely-dated (10 230Th dates) aragonite stalagmite from Lianhua Cave, Hunan Province, China. Compared to coeval stalagmites from other Chinese caves, the average δ 13C value (−3.6‰) of stalagmite A1 is higher by ~2–7‰. Variations in the δ 13C values (0.1‰ to −6.0‰) reflect changes in both vegetative productivity and inorganic processes, which respond to climatic processes. The δ 13C record of stalagmite A1 can be subdivided into three intervals: 1) warm–humid stage (6.6 to 3.8 ka); 2) transitional stage (3.8 to 1.6 ka); and 3) cool–arid stage (1.6 ka to present). Comparisons with other stalagmite and paleoclimatic records demonstrate that these intervals are generally consistent with changes in regional vegetation and climatic conditions. [Copyright &y& Elsevier]

Abstract: Paleoclimatic conditions associated with the East Asian monsoon are reconstructed for the Mid- to Late-Holocene using δ 18O values (819 measurements) from a precisely dated (10 230Th dates) aragonite stalagmite from Lianhua Cave, Hunan Province, China. δ 18O values (−1.6‰ to −7.0‰) are interpreted to reflect the precipitation amount effect related to the strength of summer monsoonal circulation. Throughout this period, the intensity of East Asian summer monsoonal circulation declined in response to changes in insolation and a southward shift in the Intertropical Convergence Zone (ITCZ). Punctuating this first-order trend are abrupt millennial- to decadal-scale fluctuations, the most prominent of which occurred around 3337±5 yr BP and records a dramatic weakening in summer monsoonal circulation that coincides with the beginning of Neoglacial conditions. Comparisons between the δ 18O values of stalagmite A1 and previously published data from stalagmite HS-4 from Heshang Cave and stalagmites D4 and DA from Dongge Cave, China, demonstrate a similar regional response to changes in East Asian monsoonal circulation. Several spectral analysis techniques and wavelet analysis were applied to these stalagmite records to evaluate the nature and character of cyclicity in the East Asian monsoon during the Holocene. Multi-Taper Method (MTM), Lomb–Scargle, and Single Spectrum Analysis (SSA) results reveal common periodicities that are unlikely to be artifacts of any single technique. The periodicities expressed in the stalagmite δ 18O records occur at both solar and non-solar frequencies and support previous interpretations that variability in monsoonal circulation responds to both solar forcing and internal climatic mechanisms. Wavelet analysis demonstrates that some of these frequencies are intermittent and recur at semi-regular intervals, which may indicate long-term cyclicity that is unconstrained by the chronology of the record. [Copyright &y& Elsevier]

Abstract: Two stalagmites from Xiangshui (X3) and Yaoba Don (YB1) Caves in southeastern China provide high-resolution δ 18O time-series that exhibit prominent millennial-scale fluctuations in the intensity and character of the Asian monsoon for the period from 20,000 to 50,000 yr. B.P. Timing of these fluctuations, established by U-series disequilibrium (230Th/234U), correlates with Dansgaard–Oeschger events (2–13) and Heinrich events (H2–H5) recorded in the GISP2 ice core, indicating a climatic link between Asian monsoon circulation and air temperatures over the North Atlantic for much of the last glaciation. Although the exact mechanisms linking climatic fluctuations in the North Atlantic to those in eastern China have yet to be identified, climatic signals associated with changes in global ice volume and air temperatures over Greenland may be transferred to Asia by atmospheric mechanisms that affect the strength of the Siberian high-pressure cell and the amount of snow cover on the Tibetan Plateau, which force the intensity of the Asian monsoon. Another mechanism linking climate of the North Atlantic to the Asian monsoon relates to variation in oceanic circulation. Millennial-scale fluctuations in thermohaline circulation in the North Atlantic may have affected ocean currents in the tropical western Pacific Ocean, which is the moisture source for the East Asian monsoon. Despite the similarity of these paleoclimatic records and the implication of global teleconnections, the magnitude and timing of millennial-scale events at different locations in China reveal regional variations in climatic conditions. Comparisons of the δ 18O curves from Xiangshui and Yaoba Don Cave stalagmites with those from Qixin Cave and Hulu Cave show general concordance between millennial-scale events, albeit with some notable differences among all the records. The well-studied Hulu Cave records show δ 18O values that are lower than those of Xiangshui and Yaoba Don Caves, reflecting geographical differences. Hulu Cave is located near the eastern coast at a relatively low elevation dominated by the East Asian monsoon. By comparison, Xiangshui Cave and Yaoba Don Cave are further inland on the eastern slope of the Yunnan–Guizhou plateau, which receives precipitation from both the East Asian monsoon and quasi-stationary frontal systems. Rainfall contributed by the East Asian summer monsoon is relatively diminished in this region by these geographic and atmospheric circulation conditions, resulting in higher δ 18O values. [Copyright &y& Elsevier]