Greenland ice cores provided the most directly and highly resolved records of glacial climate events during the past 120 000 years,but they presented different time scales for these rapid climate events.As we previously reported,precisely-dated and high-resolution cave δ18O records make it possible to correct the chronologies of Greenland ice cores.Furthermore,annual to decadal-resolved monsoon records would explore a detailed transition pattern for the climate events,providing a crucial test for physical models of abrupt climate events.Here we present such precisely-dated East Asian monsoon record between 24 and 21 ka B.P.,and then discuss a possible forcing mechanism for the climate events during the Last Glacial Maximum.The growth phase for one stalagmite from Hulu Cave,Nanjing,has been precisely dated by thermal ionization mass spectrometry and counting result for continuous annual lamination profile under microscope.A total of 727 sub-samples were scraped off from successive laminations of the polished column and their oxygen isotope composition was measured by MAT-253 mass spectrometry.Based on the 230Th dates and more than 3000-year-long duration of annual banding sequence,an average 3-year resolution stalagmite δ18O time series between 24 and 21 ka B.P.has been established.The high resolution oxygen isotope record well reflects the variation of Asian summer monsoon precipitation during the last glacial period,i.e.the more negative value of stalagmite δ18O,the higher precipitation.The stalagmite δ18O record displays large amplitude from-4.709‰ to-8.709‰ in δ18O value,suggesting that monsoon precipitation changed largely in magnitude even during the Last Glacial Maximum.We recognizes two cycles of wet/dry from this record: one is from 24.0 to 22.1 ka B.P.and the other is from 22.1 to 21.1 ka B.P.Most importantly,shorter-term climatic events are superimposed on the two millennial cycles,coherently linking to the remote climate events,such as Heinrich events in North Atlantic and Dansgaard-Oeschger events in Greenland ice core records. The precisely-dated δ18O record provided a strong support for accuracy of the GISP2 time scale.An IS2 event(or DO 2),well expressed in the Greenland ice core δ18O records,can be unambiguously identified in our record.The timing of IS2 in GISP2 is close to the chronology of the stalagmite records within the uncertainty of U/Th dates.However,GRIP and NGRIP are younger than GISP2 by 800 to 2000 years for the same event.This discrepancy among the three Greenland ice cores would come from a larger uncertainty for the ice cores: age errors up to 1% during the Holocene and the uncertainties become larger as the chronology gets older.If the time scale of GISP2 is accurate before 40 ka B.P.based on ice-layer counting,we suggest that the event was synchronous over the Northern Hemisphere. Our record,in combination with the previously-published record between 17 and 15 ka B.P.also from Hulu Cave,indicated that the monsoon events(H1 and H2),in terms of their structures,are quite different from the cold events in North Atlantic,which were well presented in the Greenland ice core δ18O records. For the both of H1 and H2,the monsoon precipitation records show a rapid transition from dry to wet conditions,followed by a stepwise increasing trend,with a total duration of more than 600 years.In contrast,the Greenland δ18O records display abrupt changes either into or out of the events.This suggests that changes of East Asian monsoon were triggered by not only the North Atlantic themorhaline circulation but also the coupled oceanic-atmospheric circulation from tropical Pacific.
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