Details Of H Events And Karst Ecological Processes Recorded By Stalagmites In Wulu Cave In Southwest Guizhou In The Middle And Late MIS 3

Millennial-scale climatic oscillations occurred during the last glacial period have been confirmed by a large number of geological records.Analyzing its transitional and internal structures is important for understanding forcing mechanisms of climate changes.In this study,19 high-precision U/Th dates,1907 isotopic(?¹⁸O and?¹³C),and trace element data were analyzed from two stalagmites from Wulu cave,southwestern Guizhou,to reconstruct Asian monsoon and ecological processes during mid to late MIS 3?Marine Isotope Stage??41.1?26.1 ka BP?.Especially,H3 and H4 events are further addressed.In ?¹⁸O profiles,H event from two samples is expressed as an irregular"V"shape,that is,a"three-stage"structure:?1?At the onset,?¹⁸O values increase,and the monsoon weakened rapidly;?2?During mid-H event,?¹⁸O decreases gradually,and the monsoon slowly increased;?3?At the end,?¹⁸O values are rapidly depleted,and the monsoon increased sharply.The unstable monsoon variability during mid-H event is widely found in other cave records in China,which is consistent with the atmospheric methane and dust records from ice cores,and low-latitude geological records.At the same time,the low Greenland temperature remained at a stable level,indicating that high-and low-latitude climates are decoupled.One possible explanation is:?1?Freshwater unputs into the North Atlantic caused a significant weakening of the Asian summer monsoon;?2?Subsequently,the injection of fresh water weakened,and the northward shift or expansion of ITCZ induced a gradual strengthening of Asian monsoon;?3?At the end,the AMOC reworked,thereby strengthening the Asian monsoon and ending the H event.On millennium scale,?¹⁸O records from two stalagmites are well reproduced,but?¹³C records are significantly different,especially during the cold period?H3,H4?.The growth rate of sample Wu81 changed significantly,and?¹⁸O and?¹³C records showed a negative correlation during the H event.Probably,the overlying soil cover is thin and the mixing time of infiltration waters is short.Therefore,during the warming event,the“over-humidity mode”occurred.This caused more carbon isotopes from the bedrock and enriched?¹³C values in the stalagmite.In sample Wu20,the deposition rate is stable,the soil cover is thick,the mixing time of infiltration waters is long,and the growth rate does not change significantly.During H3 and H4 events,less precipitation made the"over-humidity mode"insignificant,which resulted in a large amount of deposition.At the same time,the stable seepage waters and sufficient exchange between drips and soil CO₂ make?¹³C values change within a small amplitude.At centennial scale,?¹⁸O and?¹³C changes are similar during intersdatials,but are decoupled during H3 and H4 events.This may be related to the weak monsoon,less rainfall and reduced effective humidity,highlighting dynamic effects of calcite deposition such as CO₂ degassing.Trace element analysis shows that Mg/Ca did not respond significantly to abrupt climatic events.Ba/Ca and Sr/Ca can reflect infiltration conditions when the monsoon intensified.During H3 and H4,these elements may trace a source from atmospheric dust activity.Changes of elements are consistent with?¹³C records,suggesting that they are locally dependent.Probably,regional climates can influence them at millennial scale,and site-sepcific processes,i.e.,soil thickness,vegetation type,soil microbial activity,and karst,are both involved.