A High-resolution Sinkhole Record Of The Evolution Of The Asian Summer Monsoon In MIS11

Characteristics and mechanisms of millennial-scale climate during the Marine Isotope Stage 11(MIS 11)still remains to be resolved by high-resolution and precisely-dated proxy records.Here we obtain 11 230Th datings and 3410 stable isotope measurements from a 3700 mm-long stalagmite(LS60)from Luoshui Cave,Hubei Province,central China to reconstruct the Asian Monsoon climates and environment evolution from 403.7-354.1 ka B.P.,with a high resolution of 17a.Eight weak monsoon events,with amplitudes of over 1‰,are recognized superimposed on the solar insolation changes from the LS60 ?18O record.These weak monsoon events are characterized with a reoccurrence of 5-7 ka,similar to Bond cycles in the last glacial period.The first three weak monsoon events,beginning at 392.0,386.2 and 380.5 ka B.P.,respectively,all correspond to Greenland coolings,Antarctic warmings,lower Iberian Margin sea surface temperatures and IRD layers within dating errors.Considering the prominent features similar to Heinrich events and the strong agreement to bipolar seesaw mechanism,we here define them as Heinrich-like(HL)events HL1,HL2 and HL3.The HL events are also captured by another high-resolution record from a nearby Yongxing Cave.Both stalagmite records show that the rapid shifts of HL events take place within 0.3 ka,and weak mosoon periods are "flat shaped".The HL events have a pace of 6-8 ka,similar to the quasi periodicity of Heinrich events in the last ice age.It is also revealed that Heinrich and HL events occur during low solar insolation(425-455 W/11m2)periods.Differences are recognized that the onset and ending of Heinrich events are slower,and the events are both "flat shaped" and "valley shaped".A comparison with ocean and ice core record suggests HL events in MIS11 to be global events.Global millennial events are good identifiers of glacial inceptions,indicating the recovery of seesaw activities as well as the extensive ice sheet which is large enough to collapse and interrupt ocean circulation.Therefore,we use the onset of HL3 event to determine the end of MIS11c period,and find that the end should at least be earlier than 395.0 ka B.P..The total length of MIS11c is calculated to be about 31 ka,approximate to results from oceanic isotope and sea surface temperature records in the North Atlantic.Furthermore,we derive monsoon climate variabilities using power spectra and EMD analyses.Analytical results show significant variances on centennial scales,with 180a cycles corresponding to de Vries cycles,a similarity shared by monsoon climates in the Last Interglacial and the Holocene.It supports the idea that low-latitude hydrology is responsive to solar activities in the past interglacials.The LS60 ?13C record is divided into two stages,a continuous positive trend from 403.7 to 395.0 ka B.P.followed by fluctuations around an average value of-5.8‰.Its general pattern follows the global ice volume,as well as the global temperature,indicating that changes of local plant categories(C3 and C4)are controlled by orbital-scale elements.On the millennial scale,the detrended ??13C and ??18O records show a positive correlation(r=0.31,n=3306).A detailed comparison shows that stable isotope records are synchronized in HL events,with positive shifts in both profiles,supporting the existence of identified Heinrich-like events.But they are not in good agreement during other weak monsoon events,indicating different mechanisms from Heinrich events.Cross-spectra analysis shows a common periodicity of 1-3 ka of ??13C and ??18O records,suggesting that ?13C is responsive to Asian Monsoon circulation on the millennial timescale.In summary,we provide three new insights into the millennial Asian Monsoon events during MIS 11 on the basis of our decadally-resolved record:(1)HL events are comparable to Heinrich events from aspects of characteristics,frequencies and amplitudes,implying a same mechanism underneath;(2)the first weak monsoon event(HL3)after MIS 11c is determined at 392.0 ka B.P.,indicating the ending of MIS11c prior to 395.0 ka B.P.;(3)MIS11c,the interglacial used to compare with the Holocene,has a high-frequency variations internally and centennial to decadal-scale solar acitivity periodicities,providing new evidence for present climate and future predications.