Search

The penultimate deglaciation was characterized by a sub-millennial-scale warm event in the Heinrich Stadial 11(HS11), termed the 134-ka event. However, its precise timing and structure remain poorly constrained due to the lack of high-resolution and precisely dated records. We present an oxygen isotope record of a speleothem with well-developed annual lamina from Zhangjia Cave, located on the north margin of the Sichuan Basin, characterizing Asian summer monsoon (ASM) changes in the 134-ka event, which included an increase excursion of ca. 149 years and decrease excursion of ca. 200 years, inferred from 3.3‰ δ18O variations. This event also divided the weak ASM interval-II (WMI-II), corresponding to HS11, into two stages, the WMI-IIa 132.8–134.1 ka and WMI-IIb 134.4–136.4 ka. With a comparable climatic pattern globally, the 134-ka event is essentially similar to the millennial-scale events in last glacial–deglacial period. Particularly, the observed weak-strong-weak ASM sequence (138.8–132.8 ka) is largely controlled by changes in the Atlantic Meridional Overturning Circulation (AMOC) forced by the meltwater of northern high-latitude ice sheets. Moreover, our results underpin that AMOC, rather than the global ice volume, is more critical to ASM variations during the last two deglaciations. [ABSTRACT FROM AUTHOR]

Speleothem isotope records have been widely used in the forefront of paleoclimate researches. Although the oxygen isotope (δ18O) records of speleothems remain the most commonly used hydroclimate proxy, the carbon isotope (δ13C) and trace element records of speleothem have also shown their unique advantages in charactering regional-local hydroclimate variations. In this study, we present two high-resolution (seasonal-monthly) and precisely dated speleothem δ13C records (NB2 and NB3) over the past 120 years from Niubi cave in Southeast China. Our analyses show that hydroclimate-induced changes in the regional vegetation coverage appear to be the primary control on the speleothem δ13C values over the past 120 years. However, during the late 1950s to early 1960s, a large high δ13C excursion is observed in the NB record, which is apparently linked to a special human activity in China's modern history, the so-called "Great Leap Forward in Iron and Steel". We suggest that the large degree of damages to regional vegetation occurred during the time period resulted in the observed high speleothem δ13C values, as the local precipitation remained in an ordinary state inferred from δ18O and trace element data. The persistent decreasing trend in the NB δ13C record during the 1980–2018 CE may be attributed to the increased vegetation effect via increases in precipitation, temperature and atmosphere CO 2 , as well as the decrease of δ13C of atmospheric CO 2. [ABSTRACT FROM AUTHOR]

Speleothem oxygen isotope (δ18O s) record as a climatic proxy in southeastern China is still in debate due to multifaceted influencing factors, a modern δ18O s record, which can be calibrated or compared with observational data, is critical to explore the interpretation of δ18O s proxy. Here we present a seasonally resolved δ18O s record spanning the interval of 1898–2018 CE from Niubi Cave, Guangdong Province, southeastern China. A comparison between the Niubi δ18O s and instrumental data reveals that the Niubi δ18O s variability is primarily controlled by changes in precipitation seasonality modulated by El Niño-Southern Oscillation on interannual to interdecadal timescales. Higher (lower) δ18O s values correspond to lower (higher) ratios of the East Asian summer monsoon/non-summer monsoon precipitation during the El Niño (La Niña) events associated with concomitant changes in the outgoing longwave radiation, wind field and Western Pacific Subtropical High. While ∼73% historical drought events correlate to positive anomalies in Niubi δ18O s values over the last 120 years, the rest of drought events associate with the negative δ18O s anomalies. This observation suggests two different mechanisms for the drought events with more and less diminution of rainfall amount in the East Asian summer monsoon relative to the non-summer monsoon precipitation, respectively. Additionally, our Niubi δ18O s record from southeastern China, together with other high-resolution speleothem and tree ring records, demonstrate a "tripole pattern" of summer precipitation during the last ∼100 years in eastern China. • δ18O s records from SEC is controlled by the precipitation seasonality modulated by the ENSO on interannual timescales. • Not all drought events correspond to the higher δ18O s in NB cave because of the effect of precipitation seasonality. • A "tripole pattern" of summer rainfall in eastern China can be observed in palaeoclimatic records over the past ∼100 years. [ABSTRACT FROM AUTHOR]