Ice-volume and insolation influences on hydroclimate changes in central eastern China during the antepenultimate glacial period

The rainfall changes in East Asian summer monsoon(EASM)regions on the orbital timescale remain controversial due to the lack of reliable rainfall records.Here,we present new multiproxy records(δ^(18)O,δ^(13)C,Sr/Ca and Mg/Ca)of a230Thdated stalagmite from Hulu Cave in central eastern China.Multiproxy records reconstruct a regional hydroclimate history from 340 to 261 kyr BP(thousand years before present),approximately covering the antepenultimate glacial period.Theδ^(18)O record is dominated by the precessional cycles,suggesting that EASM responds to changes in Northern Hemisphere summer insolation(NHSI)on the orbital timescale.Significant correlations amongst theδ^(13)C,Sr/Ca and Mg/Ca suggest that a common factor,i.e.,the local hydrological cycle,controlled their variability,and their leading principal component can be used as a proxy linked to regional rainfall.This composite record bears a good similarity to those from the Chinese Loess Plateau,showing a gradually decreasing rainfall during the antepenultimate glacial period,consistent with changes in global ice volume.Superimposed on the long-term trend,three relative wetter intervals were responding to the higher NHSI periods,suggesting that EASM rainfall variability was induced by integrated effects of global ice volume and NHSI.The increased ice sheets and lower NHSI resulted in an increased meridional temperature gradient and southward shift of the westerlies,which shortened the duration of Meiyu and midsummer rainfall.The differences between the rainfall record and the stalagmiteδ^(18)O record indicate that the latter represents the overall EASM intensity linked to monsoon circulation,but does not directly reflect the rainfall changes at the cave sites.

Multiscale analysis of Asian Monsoon over the past 640 ka

The empirical mode decomposition(EMD) method is used to re-analyse the high-resolution and precisely-dated stalagmite record from Chinese caves over the past 640 ka. Results show that(1) the variation in the Asian Monsoon can be completely decomposed into ten quasiperiod oscillations, among which the precession and semiprecession band oscillations are the most prominent periodicities, with contribution rates of 31.1% and 30.7%, respectively;(2) the cross-spectrum analysis of the semiprecession component and bi-hemisphere insolation(BHI) are strongly correlated, indicating an amplified response of precipitation and temperature variability to the interhemispheric insolation in the low-latitude regions, thus further affecting the intensity of the Asian Monsoon;(3) on millennial timescales, obvious oscillations at the 5 ka and 1–2 ka bands roughly correspond to the classical Bond and Dansgaard-Oeschger(DO) cycles. Additionally, a strong correlation is found between the detrended stalagmite δ18 O records and Ca/Sr sequence from the North Atlantic(especially at the 5 ka band). This result means that the 5 ka cycle is characteristic of the glacial-interglacial cycle since the middle and late Pleistocene and may imply that climate change on the millennial timescale is the result of an interaction between global ice volume and insolation.