Climate Change In The Past2000Years Revealed By Stalagmites From Lianhua Cave In Northwest Hunan, China

As the global warming, the frequency of extreme events shows a higher tendency than before, many places have suffered the extreme events in the recent years in China. Such as the extreme drought happened at southwest China between2009and2010, the extreme precipitation in Beijing, July21th,2012, which threatened peoples’ lives, property, and it has also received attention from Chinese leaders. So how to deal with the extreme events is an urgent problem to our Chinese. Due to the fact that the atmospheric records are short, most of them started at1957, to research the extreme events is limited, so we need to search effective record which can reflect the extreme events in history, and the author point out using stalagmite to research the extreme events in the past2000years. After the research on230Th chronology, carbon and oxygen isotopes, elements, sedimentology of stalagmites LHD1and LHD3in Lianhua Cave, Longshan county, Hunan, China, we achived the following conclusions,(1) the stalagmites LHD1and LHD3are all aragonite, with high uranium concentration (238U>3ppm), relative high growth rate (about0.1mm/yr), and they are fit for230Th dating. After the precisely dating, the top30mm of stalagmite LHD1grows from1548AD to2011AD, the year we collected. Stalagmite LHD3grows from154BC to1510AD, the main growth time are in past2000years, so we can use these two stalagmites to research the extreme events in the past2000years.(2) the tendency of δ18O of stalagmites in Lianhua Cave reflect the summer monsoon change in hundred to thousand years scale, in annual to multi decadal scale, the δ18O reflects the precipitation in this area, and the drought-flood level in this area. Since1950s, the δ18O of stalagmite LHD1show a dramatic heavier tendency, but the precipitation changed little, so with the Asian monsoon decrease, there may be some other factors affect the δ18O of stalagmite LHD1.(3) the climate change revealed by stalagmite from the Lianhua Cave shows, before the medieval warm period, the precipitation in this area showed a decreased trend as the solar insolation decreased, in the medieval warm period, in the background of warm, this area was dominated by dry, and in the Little Ice Age, this area also showed a dry condition as the climate was cool,1850-1950AD the precipitation in this area is high, but the converse phase between δ18O and precipitation in this area since1950make us can’t use δ18O of stalagmite to construct the precipitation in this area.(4) the stalagmite in Lianhua Cave has recorded four extreme drought since the Little Ice age, the drought in the end of Ming dynasty,1680-1697AD drought,1771-1827AD drought and1896-1902AD drought, All these four drought are widely spreaded and recorded by the historical document. After compared with the drought happened in southwest China between2009and2010, we have found the same mechanism behind. When the extreme events happened, the solar activity was weak, the SST in middle east Pacific was positive anomaly, which expressed the condition of El Nino, the SST in basin of Pacific showed a negative anomaly, the PDO index was positive, and the SST in west Pacific warm pool also negative, and the summer monsoon system was weak, the west Pacific subtropical high was strong, which the position towarded south and west, so all the above circulation conditions make the extreme event happened in China monsoon area. So maybe we can use this to forecast the extreme event in the future.