A 7-cm long aragonite stalagmite, FR0510-1, from Furong Cave, Chongqing, was dated by 210Pb and 230Th methods, revealing a-2000-year record of climate history under the influence of the East Asian Monsoon. The FR0510-1 record resembles Dongge Cave DA record on 10–100-year scales, but quite different from the Wanxiang Cave WX42B record, indicating that while stalagmite δ18O record represents local/regional moisture change, spatial variability of the monsoonal rainfall over eastern China must take into account. During the past 2000 years, climate in Chongqing was relatively wet in the intervals of 50 BC–AD 250, AD 1150–1450 and AD 1600–1950, and relatively dry during the periods of AD 250–1150 and AD 1450–1600. Dry conditions were prevailing over the Medieval Warm Period, whereas wet climates were dominant during the most time of the Little Ice Age in Chongqing area.

To understand oxygen and carbon stable isotopic characteristics of aragonite stalagmites and evaluate their applicability to paleoclimate, the isotopic compositions of active and fossil aragonite speleothems and water samples from an in situ multi-year (October 2005–July 2010) monitoring program in Furong Cave located in Chongqing of China have been examined. The observations during October 2005–June 2007 show that the meteoric water is well mixed in the overlying 300–500-m bedrock aquifer, reflected by relatively constant δ18O, ±0.11–0.14‰ (1σ), of drip waters in the cave, which represents the annual status of rainfall water. Active cave aragonite speleothems are at oxygen isotopic equilibrium with drip water and their δ18O values capture the surface-water oxygen isotopic signal. Aragonite-to-calcite transformation since the last glaciation is not noticeable in Furong stalagmites. Our multi-year field experiment approves that aragonite stalagmite δ18O records in this cave are suitable for paleoclimate reconstruction. With high U, 0.5–7.2 ppm, and low Th, 20–1270 ppt, the Furong aragonite stalagmites provide very precise chronology (as good as ±20s yrs (2σ)) of the climatic variations since the last deglaciation. The synchroneity of Chinese stalagmite δ18O records at the transition into the Bølling–Allerød (t-BA) and the Younger Dryas from Furong, Hulu and Dongge Caves supports the fidelity of the reconstructed East Asian monsoon evolution. However, the Furong record shows that the cold Older Dryas (OD) occurred at 14.0 thousand years ago, agreeing with Greenland ice core δ18O records but ∼200 yrs younger than that in the Hulu record. The OD age discrepancy between Chinese caves can be attributable to different regionally climatic/environmental conditions or chronological uncertainty of stalagmite proxy records, which is limited by changes in growth rate and subsampling intervals in absolute dating. Seasonal dissolved inorganic carbon δ13C variations of 2–3‰ in the drip water and 5–7‰ in the pool and spring waters are likely attributed to variable degrees of CO2 degassing in winter and summer. The variable δ13C values of active deposits from −11‰ to 0‰ could be caused by kinetically mediated CO2 degassing processes. The complicated nature of pre-deposition kinetic isotopic fractionation processes for carbon isotopes in speleothems at Furong Cave require further study before they can be interpreted in a paleoclimatic or paleoenvironmental context.

We present a highly precise, 230Th / U-dated, 1.5-year resolution d18O record of an aragonite stalagmite (LHD1) collected from Lianhua Cave in the Wuling Mountain area of central China. The comparison of the d18O record with the local instrumental record and historical documents indicates that (1) the stalagmite d18O record reveals variations in the summer monsoon intensity and dry–wet conditions in the Wuling Mountain area. (2) A stronger East Asian summer monsoon (EASM) enhances the tropical monsoon trough controlled by ITCZ (Intertropical Convergence Zone), which produces higher spring quarter rainfall and isotopically light monsoonal moisture in the central China. (3) The summer quarter/spring quarter rainfall ratio in central China can be a potential indicator of the EASM strength: a lower ratio corresponds to stronger EASM and higher spring rainfall. The ratio changed from <1 to >1 after 1950, reflecting that the summer quarter rainfall of the study area became dominant under stronger influence of the Northwestern Pacific High. Eastern China temperatures varied with the solar activity, showing higher temperatures under stronger solar irradiation, which produced stronger summer monsoons. During Maunder, Dalton and 1900 sunspot minima, more severe drought events occurred, indicating a weakening of the summer monsoon when solar activity decreased on decadal timescales. On an interannual timescale, dry conditions in the study area prevailed under El Niño conditions, which is also supported by the spectrum analysis. Hence, our record illustrates the linkage of Asian summer monsoon precipitation to solar irradiation and ENSO: wetter conditions in the study area under stronger summer monsoon during warm periods, and vice versa. During cold periods, the Walker Circulation will shift toward the central Pacific under El Niño conditions, resulting in a further weakening of Asian summer monsoons.

The frequent alternation between droughts and floods in the karst regions of Southwestern China has a serious impact on the ecological environment and socio-economic development. Although some high-resolution records for this region have been published, there is a lack of multi-proxy geological records that could be used to reconstruct the relationships between the changes in the Asian summer monsoon (ASM) and the regional hydrology and ecological environment since the Late Holocene. In this study, the history of the ASM from 3109 to 694 yr BP with a mean temporal resolution of 2.5 yr is reconstructed based on 47 high-precision 230Th dating results (mean 2-sigma error of +-14 yr), 959 pairs of d18O/d13C data, and multiple trace element analyses of a stalagmite from Shijiangjun (SJJ) Cave in the karst area of Southwestern China. The positive d18O and d13C excursions accurately recorded eight interdecadal-centennial weak summer monsoon events at ~779, 1013-911, 1282-1172, 1736-1638, 1961-1864, 2472-2375, 2931-2818, and 3050-3014 yr BP. The cross-wavelet spectrum analysis of the d18O and d13C of stalagmite SJJ7 indicates that they have similar periods. The 7 yr period of the d18O record was determined to have the maximum contribution rate (36.8%) to the periods using ensemble empirical mode decomposition (EEMD) analysis. In the Late Holocene, the weak ASM events were dominated by the southward shift of the Intertropical Convergence Zone (ITCZ) and the frequent El Nino events on an interdecadal-centennial timescale. The southward migration of the ITCZ lead to frequent El Nino events, and the resultant Hadley Circulation and Walker Circulation were weakened, leading to a weak ASM and changes in the hydrological conditions in the monsoon region. The d13C values of the stalagmite changed relatively slowly compared with the d18O values, which may indicate that the degradation and restoration of the regional ecological environment caused by abrupt changes in the climate is a relatively slow process. When the summer monsoon decreased, the stalagmite's Mg/Ca and Sr/Ca ratios were relatively high due to CO2 degassing, and the prior calcite precipitation (PCP)/prior aragonite precipitation (PAP) increased in the karst zone. However, the Mg/Ca ratio increased and the Sr/Ca ratio rapidly decreased during the calcite deposition due to differences in the crystal structures and partition coefficients of aragonite and calcite. The dark layers in stalagmite SJJ7 correspond to transition from heavy to light d18O values, reflecting the transition in the ASM. The pulsed increases in the elements (Mn, Fe, Al, and Si) in the dark layers reflect the stronger mechanical transport caused by more rainfall. The multi-proxy analysis of this stalagmite may reflect the interactions between the changes in the ASM and the atmosphere-hydrosphere-pedosphere-biosphere-lithosphere in the karst critical zone during the Late Holocene.

Based on 33 U/Th dates and 1020 oxygen isotopic data from stalagmite Y1 from Yamen Cave, Guizhou Province, China, a record of the Asian Summer Monsoon (ASM) was established. The record covers the last deglaciation and the early Holocene (from 16.2 to 7.3 ka BP) with an average oxygen isotope resolution of 9 years. The main millennial-scale deglacial events first identified in Greenland (Greenland Interstadial Events: GIS 1e through GIS 1a) and later in China are clearly present in the Y1 record. By analogy to earlier work, we refer to these as Chinese Interstadials (CIS): CIS A.1e to CIS A.1a. The onset of these events in Y1 d18O records are nominally dated at: 14750±50, 14100±60, 13870±80, 13370±80, and 12990±80 a BP. The end of CIS A.1a or the beginning of the Younger Dryas (YD) event is nominally at 12850±50 a BP and the end of the YD dates to 11500±40 a BP. The d18O values shift by close to 3 per mil during the transition into the Bolling-Allerod (BA, the onset of CIS A.1e) and at the end of the YD. Comparisons of Y1 to previously published early Holocene records show no significant phase differences. Thus, the East Asia Monsoon and the Indian Monsoon do not appear to have been out of phase during this interval. The Y1 record confirms earlier work that suggested that solar insolation and North Atlantic climate both affect the Asian Monsoon.

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 d18O and d13C, mostly in the 2.3-26 cm part. The d18O and d13C 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 d18O 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 d18O 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 d18O peak around 60 ka, indicating significant weakening of the monsoon in Chongqing during the cold period.The XY2 d18O 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 d18O 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.

Thorium-230 ages and oxygen isotope ratios of stalagmites from Dongge Cave, China, characterize the Asian Monsoon and low-latitude precipitation over the past 160,000 years. Numerous abrupt changes in 18O/16O values result from changes in tropical and subtropical precipitation driven by insolation and millennial-scale circulation shifts. The Last Interglacial Monsoon lasted 9.7 ± 1.1 thousand years, beginning with an abrupt (less than 200 years) drop in 18O/16O values 129.3 ± 0.9 thousand years ago and ending with an abrupt (less than 300 years) rise in 18O/16O values 119.6 ± 0.6 thousand years ago. The start coincides with insolation rise and measures of full interglacial conditions, indicating that insolation triggered the final rise to full interglacial conditions.

Two stalagmites from Xiangshui (X3) and Yaoba Don (YB1) Caves in southeastern China provide high-resolution d18O 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 d18O 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 d18O 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 d18O values.

We present a continuous record of the Asian monsoon over the last 16 ka from d18O measurements of stalagmite calcite. Over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230Th dates. d18O and therefore Asian monsoon intensity generally follows changes in insolation,although changes in d18O are generally accommodated in abrupt shifts in contrast to smoothly varying insolation, indicating that threshold effects may be important. d18O decreased dramatically (~3 per mil) at the start of the Holocene (~11.5 ka) and remained low for ~6 ka. Four positive d18O events centered at 11225±97 yr BP (1.05 per mil), 10880±117 yr BP (1.15 per mil), 9165±75 yr BP (1.4 per mil), and a double event centered at 8260±64 yr BP (1.1 per mil) and 8080±74 yr BP (1.0 per mil) punctuated this period of high monsoon intensity. All four events correlate within error with climate changes in Greenland ice cores. Thus, the relationship between the Asian monsoon and the North Atlantic observed during the glacial period appears to continue into the early Holocene. In addition, three of the four events correlate within error with outburst events from Lake Agassiz. The decline of monsoon intensity in the mid-late Holocene is characterized by an abrupt positive shift in d18O which occurs at 3550±59 yr BP (1.1 per mil in ~100 yr). In addition, the Holocene is punctuated by numerous centennial- and multi-decadal-scale events (amplitudes 0.5 to 1 per mil) up to half the amplitude of the glacial interstadial events seen in the last glacial period. Thus, Holocene centennial and multi-decadal-scale monsoon variability is significant, although not as large as glacial millennial-scale variability. The monsoon shows a strong connection with northern South American hydrological changes related by changes in ITCZ position. Spectral analysis of the d18O record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing. However, there are numerous other significant peaks including peaks at El Nino frequencies (observed for high-resolution portions of the record between 8110 and 8250 yr) which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling Holocene monsoon climate. In addition, for this high-resolution portion, we observe a distinctive biennial oscillation of the Asian monsoon, which has been associated with the Tropospheric Biennial Oscillation (TBO).

Speleothem samples from Hulu (eastern China, 32°30'N, 119°10'E) and Dongge (southern China, 25°17'N, 108°5'E) Caves provide a nearly continuous record of the Asian monsoon over the last 160 ka [Wang et al. 2001, Yuan et al. 2004]. We have obtained higher resolution data in the interval between ~99 and 146 ka B.P., providing a detailed account of d18O variations over most of MIS 5 and the latter portion of MIS 6. Precise 230Th dating has replicated the chronology of the samples within error. The higher resolution data set confirms the timing of Asian Monsoon Termination II (the midpoint of the negative shift in d18O marking the onset of the Last Interglacial Asian Monsoon), placing it at 129.0 ą 0.9 ka B.P. The bulk of this transition (~1.7 per mil) took place within approximately 70 years, with the total range of the transition being 3 per mil. The most abrupt portion of the shift in d18O values ( 1.1 per mil) marking the end of the Last Interglacial Asian Monsoon occurred in ~120 years, the midpoint of which is 120.7 ą 1.0 ka B.P. The Dongge Cave monsoon d18O record over late MIS 6 exhibits a series of sub-orbital millennial-scale climate shifts that average 1.3 per mil in magnitude and occur on average every 1.8 ky. Abrupt shifts in d18O of up to 1 per mil also occurred throughout the Last Interglacial Asian Monsoon, with periods at multi-decadal to centennial timescales. Similar to the amplitude and periodicities of events found by Dykoski et al. during the Holocene in the Dongge record, these shifts cover more than 1/2 of the amplitude of millennial-scale and multi-centennial-scale interstadial events during the Last Glacial Period [Wang et al. 2001] and millennial-scale and multi-centennial-scale interstadial events during the Penultimate Glacial Period in China (this study). Abrupt decadal to millennial-scale climate events therefore appear to be a general feature of both glacial and interglacial climate. We demonstrate that monsoon intensity correlates well with atmospheric CH4 concentrations over the transition into the Bølling-Allerød, the Bølling-Allerød, and the Younger Dryas. In addition, we correlate an abrupt jump in CH4 concentration with Asian Monsoon Termination II. On the basis of this correlation, we conclude that the rise in atmospheric CO2, Antarctic warming, and the gradual portion of the rise in CH4 around Termination II occur within our ""Weak Monsoon Interval"" (WMI), an extended interval of heavy d18O between 135.5 ą 1.0 and 129.0 ą 1.0 ka B.P., prior to Asian Monsoon Termination II and Northern Hemisphere warming. Antarctic warming over the millennia immediately preceding abrupt northern warming may result from the ""bipolar seesaw"" mechanism. As such warming (albeit to a smaller extent) also preceded Asian Monsoon Termination I, the ""bipolar seesaw"" mechanism may play a critical role in glacial terminations.