High Resolution Stalagmite Record From Wanxiang Cave During The Last Deglaciation

During the last deglaciation, global climate represented one of the largest and most rapid natural climate changes in Earth’s recent history, dramatic and clear climate variations of the climate supplied us lots of important study materials in the understanding of the climate system and its forcing mechanisms, have been arousing great interest in the paleoclimate research. The Asian monsoon system is an important part of the global climate system, which connects the westerly belt to the north and the low-latitude over-equator monsoon system to the south, actively carries the meridional and zonal climatic signals transportation, in the capacity of a ligament of the high latitude ice caps-ocean system-atmosphere circulation. Meanwhile, the monsoon effected area load supporting a majority of population of our country, the advance and retreat of the monsoon which links to the precipitation variation relatives to national economy and the people’s livelihood. Hence, the research about the Asian monsoon system have an important and crucial scientific and reality significance.Wanxiang Cave locates on the margin of modern summer monsoon effect area, northwest of China, the climate is semi-Arid, sensitively to the variation of the monsoon intensity. Moreover, in this region, still lack of exactly dated high resolution climate records during the last deglaciation. Hence, stalagmite records from Wanxiang Cave during this time period have an important scientific significance. In this paper, we choose a stalagmite from Wanxiang Cave, grown during the last deglaciation as our study object,14 high precision 230Th dating data,1178 carbon and oxygen isotope pares were obtained and a 4-yr resolution precipitation and vegetation evolution time series were established. Besides, through the numerical statement of the 7857 sub-samples during the high resolution manual sub-sample cutting works and the treatment of the scan image, obtained the density and gray scale time series of the stalagmite. Through the data analysis and comparison with other climate records, got the main conclusions as bellow:1. Wanxiang Cave stalagmiteδ18O andδ13C records reflect the advance and retreat of the Asian monsoon in the western loess plateau in detail, through the comparison with other climate records, the climate of western loess plateau shows an gradually retreat of the Asian monsoon after the Heinrich levent, and the stalagmiteδ18O records from Wanxiang and Hulu Cave are inconsistent in trend, this may indicated that during the coldest time period of the H1 cold reversal, the north margin of the Asian summer monsoon may stepped back to the south of Wanxiang Cave. Meanwhile, during the Bolling/Allerod(B/A) warming, Wanxiang Cave stalagmiteδ18O record shows a gradually warming process, the starting time accords with Hulu stalagmite and Greenland ice core records. During the B/A warm period, the temperature recorded by Greenland ice core shows a gradually decrease and the Asian monsoon intensity recorded by Hulu stalagmite record shows a stable time period, but Wanxiang Caveδ18O record still keep the decrease trend as the B/A warmming, this may indicates the effect of the Asian monsoon turns more obviously during this time period in the northwest China, follows the rising sea level and the retreat of the ice-cap in the north.2. On the high frequency variation characteristics,δ13C andδ18O records from Wanxiang Cave represents an almost the same variation shapes, may reflects that the vegetation status rapidly responds to the monsoon precipitation variations in the western loess plateau. During the H1 cold event,δ13C shows an dramatically variations, the amplitude reached to 4%o, indicated that during H 1 events, as a result of the quit of the summer monsoon, the vegetation habitat worsened dramatically, extremely sensitive to the precipitation’s variation. After the B/A warming,δ13C andδ18O present a same change trends, the decrease ofδ13C andδ18O indicates the strengthen of the summer monsoon and the upturn of the vegetation condition.3. During the stalagmite deposition progress, the chemical and material components, environmental temperature, vegetation and soil conditions variations may cause to change of the calcite crystal shape and arrangements, detrital materials and trace elements in the stalagmite, all these changes may lead to the change of the stalagmite density, so, stalagmite density may recorded the climate change information during its growth period.4. Stalagmite gray scale record from Wanxiang Cave reflects the chemical and material components, cave water dynamics during its growth, the high frequency variation of the gray scale record appears an opposite change characteristics with density index, illustrate that the calcite crystal formation, crystal arrangements is the primary control factor of the stalagmite density and gray scale.5. The inner structure of H 1 event appears a distinctly double-peak characteristic, the main cooling process continued about 170 a, this cooling process appears an "three-steps" cooling,δ18O increased about 2%o, and the time of the occurrence is in agreement with Hulu record within the dating error.