ASIAN MONSOON CHANGES ON CENTENNIAL-SCALE AND CHARACTERS OF HEINRICH EVENTS DURING THE MIS 3/2 TRANSITION FROM A STALAGMITE RECORD IN SOUTHWEST CHINA

Abstract

A high-resolution stalagmite oxygen isotope record from the Wulu Cave,based on 371 oxygen isotope measurements and 12 precise 230Th dates,has provided a detailed Asian summer monsoon(ASM) history from 29 to 20.8 kaBP,spanning the marine isotope stage 3 and 2.The calcite δ18O records are essentially similar with the previously reported Hulu record formed during the same stage,although they are geographically far away(about 1,000 kilometers between the two sites).This supports the idea that changes in speleothem δ18O may represent variations in isotopic composition of precipitation associated with large-scale summer monsoon circulation over a large portion of China.Stalagmite Wu32 exhibits a first order increasing trend of δ18O values,which follows the changes in northern summer insolation.Superimposed on the long-term trend are a number of centennial-millennial scale monsoon events.The distinct positive excursions in δ18O exhibit a striking correlation with the Greenland Ca2+ record and ice-rafting events in the North Atlantic.This indicates that atmospheric circulation changes are important in transmitting abrupt climate signals globally and implies that the Asian summer monsoon is likely anti-phased with the winter monsoon on centennial to millennial-scales.Two remarkable weak summer monsoon events at 25.7 and 24.2 kaBP,indicated by a large abrupt 1.5 shift in δ18O,are coincident with H2b and H2a in the North Atlantic within error.The two peaks in H2 event are identical to those in H1,suggesting a common driving force of the H1 and H2 events.