Knowledge of Holocene hydro-climatic conditions in northern China from high temporal resolution stalagmites collected from Lianghua Cave

Our understanding of hydro-climatic dynamics in the East Asian monsoon region during the Holocene was obstructed by very few absolutely dated and high temporally resolved proxy records in northern China. Here we present duplicated carbonate δ18O records of six stalagmites with sub-decadal to multi-decadal temporal resolutions from Lianhua cave to reveal a detailed transition of the East Asian Summer Monsoon (EASM) intensity in northern China from 11.5 thousand years ago (hereafter, ka BP, before 1950 AD). Our composite records show that solar forcing dominated hydro-climatic changes, including an intensified monsoon at the Holocene Optimum from the end of Younger Dryas to 6.5 ka BP, and a subsequent multi-millennial weakening of monsoon intensity, that agree with cave records in central and southern China. However, the EASM has retreated southwards more rapidly than the Indian summer monsoon after ∼6.5 ka BP, resulting in some rapid onset of dry conditions occurring at 4.0 ka BP in northern China, which is ∼2000 years earlier than in central and southern China. This asynchrony may be related to the different regional responses among the coupling of the EASM, Indian summer monsoon, the solar forcing, and the differences in thermal forcing due to complex geographical configurations. In addition, a relative enrichment of 1h in our δ18O data of Lianhua record from 9.5 to 8.1 ka BP shows that the Holocene Optimum was punctuated by a millennial-long weak monsoon interval, which is not registered among previous cave records in central and southern China. The freshwater-induced cold climate conditions in the North Atlantic region could create stronger East Asian winter monsoon and induce a weakened EASM and a southward shift of precipitation band in northern China. Therefore, it shall not be surprised that there are strong heterogeneities among regional hydro-climatic conditions across monsoonal China in the Holocene, given the complex interplay between external and internal forcing mechanisms over the entire Holocene

Asian monsoon dynamics at Dansgaard/Oeschger events 14-8 and Heinrich events 5-4 in northern China

A precisely 230Th-dated stalagmite oxygen isotope (δ18O) record from Dragon Cave,Shanxi Province, northern China, is proposed to reconstruct the millennial-scale changes of the East Asian Summer monsoon (EASM) during the period 53.2-1.3 ka BP (before 1950 AD). Our record shows significant millennial-scale oscillations that match in timing, characteristic, and duration with the Dansgaard/Oeschger (DO)30 events 14-8 and the Heinrich events 5, 4, 2, and 1 (hereafter H5, H4, H2 and H1) in high-latitude regions of the Northern Hemisphere. Especially, the H5 event is well constrained from 48.1 to 46.9 ka BP with ten 230Th dates. Our chronology supports the NGRIP GICC05 timescale from 50 to 38 ka BP. A comprehensive comparison of the Chinese speleothem records from different regions along a north-south transect shows a unique trend towards more negative δ 18O values from 48.0 to 38.0 ka BP, suggesting that an intensified Asian summer monsoon (ASM) across the whole monsoonal China during the interval. We speculate that the joint effect, from both the cooling of the Southern Hemisphere and the enhanced land-sea temperature contrast due to the rising summer insolation, is capable to regulate the low-latitude large-scale atmospheric circulation patterns and exert significant influences on the long-term ASM variations during the middle of Marine Isotope Stage 3

A Review of Research Progress on the Analytical Method of Large-<i>n</i> Detrital Zircon U-Pb Geochronology

BACKGROUND: Detrital zircon U-Pb geochronology is an important tool for identifying sedimentary provenance and determining the maximum depositional age. The numbers of grains for detrital zircon provenance investigations using laser-ablation inductively coupled-plasma mass spectrometer (LA-ICP-MS) typically range from 60 to 120. In this range, age components are commonly not identified from the sample aliquot. In order to improve the reliability of provenance investigation, analysis of more grains (n ≥ 300) or even the large-n aliquot with more than 1000 grains (n>1000) are required. The emergence of large-n detrital zircon U-Pb geochronology is challenging the methods of data measurement, reduction and evaluation.OBJECTIVES: To summarize the progress of measurement, data reduction and data evaluation of large-n detrital zircon U-Pb geochronology.METHODS: By summarizing the method innovation of domestic and foreign literature.RESULTS: Firstly, each measurement requires rapid acquisition of U and Pb isotope signals, which can be conducted by improving the transmission efficiency of aerosol. The "flat" signal acquisition time can be shortened or transformed to a "peak" signal mode for rapid measurement. Secondly, large-n data require efficient data reduction protocol or powerful software (e.g. iolite) to improve visualization and reduce the variability between inter-laboratory comparisons. For U-Pb data processing flow, several optimized methods are introduced for fractionation correction and propagating uncertainty. In addition, total integrated counts and linear regression correction are introduced to specially process "peak" signals. Thirdly, the new calculation method of U-Pb and Pb-Pb age discordance, such as using Aitchison concordia distance, makes data filtering more reasonable. Based on recent research progress, the future of automation and standardization of large-n detrital zircon U-Pb geochronology is discussed and advice on the selection of instruments and reduction software is provided.CONCLUSIONS:In the future, the development of large-n detrital zircon U-Pb geochronology has great prospects, and will play a greater role in the study of provenance tracing and stratigraphic dating

A detailed East Asian monsoon history surrounding the ‘Mystery Interval’ derived from three Chinese speleothem records

The ‘Mystery Interval’ (MI, 17.5−14.5 ka) was the first stage of the last deglaciation, a key interval for understanding mechanisms of glacial–interglacial cycles. To elucidate possible causes of the MI, here we present three high-resolution, precisely dated oxygen-isotope records of stalagmites from Qingtian and Hulu Caves in China, reflecting changes in the East Asian summer monsoon (EASM) then. Based on well-established chronologies using precise 230Th dates and annual-band counting results, the two-cave δ18O profiles of ~ 7-yr resolution match well at decadal timescales. Both of the two-cave records document an abrupt weakening (2‰ of δ18O rise within 20 yr) in the EASM at ~ 16.1 ka, coinciding with the transition of the two-phased MI reconstructed from New Mexico's Lake Estancia. Our results indicate that the maximum southward displacement of the Intertropical Convergence Zone and associated southward shift of polar jet stream may generate this two-phase feature of the MI during that time. We also discover a linear relationship among decreasing EASM intensity, rising atmospheric CO2 and weakening Atlantic Meridional Overturning Circulation between the MI and Younger Dryas episodes, suggesting a strong coupling of atmospheric/oceanic circulations in response to the millennial-scale forcing, which in turn regulates global climate changes and carbon cycles

Strong coupling of Asian Monsoon and Antarctic climates on sub-orbital timescales

There is increasing evidence that millennial-scale climate variability played an active role on orbital-scale climate changes, but the mechanism for this remains unclear. A 230Th-dated stalagmite δ18O record between 88 and 22 thousand years (ka) ago from Yongxing Cave in central China characterizes changes in Asian monsoon (AM) strength. After removing the 65°N insolation signal from our record, the δ18O residue is strongly anti-phased with Antarctic temperature variability on sub-orbital timescales during the Marine Isotope Stage (MIS) 3. Furthermore, once the ice volume signal from Antarctic ice core records were removed and extrapolated back to the last two glacial-interglacial cycles, we observe a linear relationship for both short- and long-duration events between Asian and Antarctic climate changes. This provides the robust evidence of a link between northern and southern hemisphere climates that operates through changes in atmospheric circulation. We find that the weakest monsoon closely associated with the warmest Antarctic event always occurred during the Terminations. This finding, along with similar shifts in the opal flux record, suggests that millennial-scale events play a key role in driving the deglaciation through positive feedbacks associated with enhanced upwelling and increasing CO2.Published versio

Reconciliation of hydroclimate sequences from the Chinese Loess Plateauand low-latitude East Asian Summer Monsoon regions over thepast 14,500 years

We discuss replicated stalagmite &delta;18O records with interannual-to-multidecadal resolution from Lianhua Cave on the Chinese Loess Plateau to illustrate the precipitation history of the East Asian Summer Monsoon (EASM) region over the last 14.5 thousand years (ka BP, before 1950 CE, hereafter), and to re-evaluate the inconsistency in the proxy-inferred palaeoclimate time series in northern China. Agreement between the stalagmite &delta;18O from Lianhua and other caves from central-southern China indicates that regional climate changes after the Last Glacial were concurrent across mainland China, indicating that insolation was the primary factor controlling the evolution of the Asian Summer Monsoon (ASM). The stalagmite 18O enrichment of 2.5&permil; in the Younger Dryas and 1.7&permil; during the 8.2-ka BP event in Lianhua were larger than those in caves from central and southern China. The evidence suggests that different meridional responses of weak precipitation conditions in the ASM realm occurred during these two abrupt events, driven by high-latitude forcing in the Northern Hemisphere. The heterogeneous hydroclimate sequences in northern China inferred from different natural archives are most likely attributable to the complexity of the formations and/or some chronological uncertainty.</p

Hydroclimate changes across the Amazon lowlands over the past 45,000 years

Reconstructing the history of tropical hydroclimates has been difficult, particularly for the Amazon basin—one of Earth’s major centres of deep atmospheric convection1,2. For example, whether the Amazon basin was substantially drier3,4 or remained wet1,5 during glacial times has been controversial, largely because most study sites have been located on the periphery of the basin, and because interpretations can be complicated by sediment preservation, uncertainties in chronology, and topographical setting6. Here we show that rainfall in the basin responds closely to changes in glacial boundary conditions in terms of temperature and atmospheric concentrations of carbon dioxide7. Our results are based on a decadally resolved, uranium/thorium-dated, oxygen isotopic record for much of the past 45,000 years, obtained using speleothems from Paraíso Cave in eastern Amazonia; we interpret the record as being broadly related to precipitation. Relative to modern levels, precipitation in the region was about 58% during the Last Glacial Maximum (around 21,000 years ago) and 142% during the mid-Holocene epoch (about 6,000 years ago). We find that, as compared with cave records from the western edge of the lowlands, the Amazon was widely drier during the last glacial period, with much less recycling of water and probably reduced plant transpiration, although the rainforest persisted throughout this time.NRF (Natl Research Foundation, S’pore)Accepted versio