A High-resolution Stalagmite Study On The Evolution Of The Asian Monsoon During The Last Glacial Period

The study of the glacial period climate is the key on the paleoclimate research.There are many great achievements in the last glacial,but the study of older glacial period(such as the penultimate glacial period)still exist a lot of unresolved problems.In the thesis,a stalagmite(LS30)was collected from LuoShui cave,Hubei province.A high resolution sequence of Asian Summer Monsoon from orbit to millennial scale(170～135 ka B.P.,average resolution is 36 a)is reconstructed during the penultimate glacial based on the 29 high-precision U/Th dates and 1588 δ18O and 813C data.The upper part of the stalagmite LS30 is continuously deposited(0～892mm).There are 15 sedimentary cycles and different time length hiatus in the lower half of LS30(893～1458mm).The δ18O in LS30 is coherence with other stalagmite records at same the time(Hulu cave,Sanbao cave and Yangkou cave)in changing patterns and details.They all follow NHSI in orbit scale and superimpose the millennial scale climate oscillations.This shows that LS30 δ18O has a good repeatability with other records and can be regarded a reliable proxy of the Asian Monsoon intensity.New residual signal(△δ18)of removing NHSI(sensible heat signal)from LS30δ18O still presents orbital or suborbital trends,which indicates that the impact of orbital factors on millennial scale events can not be ignored.Comparison between△δ18O and EDC ice core δD(a proxy of Antarctic temperature change)reveals that both of them have strong synchronous anti-phase relationship on suborbital and millennial scale.This shows that Asian Monsoon intensity is driven more obviously by the latent heat release from the southern hemisphere(especially the Southern Ocean)after removing the NHSI.The Southern Ocean temperature changes drive corresponding changes of Mascarene High Pressure and Australia High Pressure,then change the cross equatorial air flow and the position and intensity of Western Pacific subtropical high Pressure,thus influence the intensity of Asian Summer Monsoon.In addition,△δ18O record supports the model of sharp change in the Antarctic temperature at MIS6.4,which means that the Antarctic "reservoir effect " is weakened or even disappeared at the background of extremely heavy ice volume in the penultimate glacial period.This phenomenon indicates that the heat storage and climate response of the Southern Ocean are different in the diverse climate boundaries.After removing the signal of orbital scale,the δ18O and δ13C appear positive correlation,which is probably because the δ13C indicates soil moisture related to precipitation.The correlation between δ18O and δ13C reflects the evolution of climate and environment at the cold and dry climate background in penultimate glacial period.15 sedimentary cycles and their changes in lithology correspond to the changes of climate or the adjustment of cave system.Lithologic analysis shows that the tawny and multihole sedimentary cycles correspond to warm and humid climate in the interglacial period,on the contrary,gray and gray-brown sedimentary corresponds to the cold dry climate at the end of the ice period.There are 12 sedimentary cycles accompanied by the progress of positively biased δ13C.This may reflect the decrease of soil moisture,the decrease rate of the mother liquid of stalagmite and the strengthening of the PCP effect.