The density of a stalagmite(WX42A)from Wanxiang Cave,Wudu County,Gansu Province,China,in the western margin of the Asian summer monsoon region,presents regular fluctuations in different deposition periods during the l...The density of a stalagmite(WX42A)from Wanxiang Cave,Wudu County,Gansu Province,China,in the western margin of the Asian summer monsoon region,presents regular fluctuations in different deposition periods during the last deglaciation.Over long timescales,high-precision 230Th dating and high-resolution stalagmite density data indicate that the density-time series between 17644 a BP and 12758 a BP is quite similar to the stalagmite δ18O record which reflects Asian monsoon intensity.Strengthening/weakening(lighter/heavier stalagmite δ18O values)of the Asian monsoon is accompanied by increase/decrease in stalagmite density.Over short timescales,decrease in stalagmite density correlates to monsoon-retreat events such as the Inter-AllerФd Cold Period(IACP),Older Dryas(OD)and Inter-BФlling Cold Period(IBCP).Generally,this kind of decrease in stalagmite density reflects precipitation decrease with weakening of the Asian monsoon,which in turn slows cave dripwater rate and decreases crystal nuclei,leading to enlargement of calcite crystals,weakened biological activity and decreased soil pCO2 which increases the abundance of impure detrital materials in stalagmites.However,during the period of large amplitude reduction of precipitation and biological activity which resulted from extreme monsoon-retreat events,temperature variation would dominate fluctuation of stalagmite density.For example,stalagmite density increased suddenly when temperature dropped suddenly in the north Atlantic during Heinrich event 1(H-1).This may be caused by low seepage water temperature,more dissolved calcium carbonate,compact regular crystals forming under higher supersaturation,leading to the stalagmite increased density.Stalagmite density fluctuation sensitively recorded stalagmite growth history and environment,demonstrating that stalagmite density can be used as a proxy for paleoclimatic research.展开更多
We explored a time series of the Asian summer monsoon(ASM) variability during the transition period from the middle to the late Holocene in the marginal Asian monsoon region. We used an absolutely dated ^(230)Th recor...We explored a time series of the Asian summer monsoon(ASM) variability during the transition period from the middle to the late Holocene in the marginal Asian monsoon region. We used an absolutely dated ^(230)Th record with only a ~20-year dating error, and oxygen isotope data with an 8-year average temporal resolution from the top 22-mm segment of stalagmite WXB07-4 from Wanxiang Cave, western Loess Plateau. The ASM intensity weakened gradually from 6420 to 4920 a BP, which was mainly characterized by three phases:(1) a strengthening phase with a higher precipitation amount between 6420 and 6170 a BP;(2) a smooth fluctuating interval during 6170–5700 a BP; and(3) a sudden extreme weakening period from 5700 to 4920 a BP. Interestingly, the extreme weakening interval of the ASM occurred during the period between 5700 and 4920 a BP, an abrupt change dated at 5430 a BP, which is known as the 5400 a BP, or 5.4 ka BP, event. The period included 290 years of gradual weakening, and 350 years of slow strengthening. This was synchronous with some cave records from the Asian monsoon region within dating errors. Comparing with Chinese archaeological archives over the past 7000 years, the early decline of the Yangshao Culture in the Yellow River Basin and the Hongshan Culture in the West Liao River Basin occurred during the period of gradual decrease of ASM precipitation. The dramatic decline in precipitation, caused by the extreme weakening of the ASM at 5400 a BP,may have been partly related to the decline of the Miaodigou Culture at the Yangguanzhai site in the Weihe River valley; the middle Yangshao Culture in western Henan in the Yellow River Basin; the early Dawenkou Culture on the lower reaches of the Yellow River; and the middle Hongshan Culture in the west of the Liaohe River valley. During the later period of the 5400 a BP event(5430–4920 a BP), a small amplitude increase and a subsequent sharp decrease of ASM precipitation may have also been linked to the contemporaneous prosperity and disappearance of the late Yangshao and Hongshan cultures; the disappearance of the late Yangshao Culture represented by the Yangguanzhai site in the Guanzhong basin on the Weihe River; the fourth phase of the late Yangshao Culture on the upstream Dadiwan site; the beginning of the middle Dawenkou Culture, the formation of its late stage,and the rise of the Longshan culture; and the rise of the Qujialing and Liangzhu cultures on the lower Yangtze River. Compared with the stalagmite precipitation records on the Qinghai-Tibetan Plateau, the rise and expansion of the Majiayao Culture in the upper Yellow River valley at 5300 a BP may have also been connected to the more dramatic increase of the summer monsoon precipitation at higher, rather than lower, altitudes during the late 5400 a BP event.展开更多
基金supported by the National Natural Science Foundation of China(40973007 and 40772110)the Specialized Research Fund for the Doctoral Program of Higher Education(200807300030)
文摘The density of a stalagmite(WX42A)from Wanxiang Cave,Wudu County,Gansu Province,China,in the western margin of the Asian summer monsoon region,presents regular fluctuations in different deposition periods during the last deglaciation.Over long timescales,high-precision 230Th dating and high-resolution stalagmite density data indicate that the density-time series between 17644 a BP and 12758 a BP is quite similar to the stalagmite δ18O record which reflects Asian monsoon intensity.Strengthening/weakening(lighter/heavier stalagmite δ18O values)of the Asian monsoon is accompanied by increase/decrease in stalagmite density.Over short timescales,decrease in stalagmite density correlates to monsoon-retreat events such as the Inter-AllerФd Cold Period(IACP),Older Dryas(OD)and Inter-BФlling Cold Period(IBCP).Generally,this kind of decrease in stalagmite density reflects precipitation decrease with weakening of the Asian monsoon,which in turn slows cave dripwater rate and decreases crystal nuclei,leading to enlargement of calcite crystals,weakened biological activity and decreased soil pCO2 which increases the abundance of impure detrital materials in stalagmites.However,during the period of large amplitude reduction of precipitation and biological activity which resulted from extreme monsoon-retreat events,temperature variation would dominate fluctuation of stalagmite density.For example,stalagmite density increased suddenly when temperature dropped suddenly in the north Atlantic during Heinrich event 1(H-1).This may be caused by low seepage water temperature,more dissolved calcium carbonate,compact regular crystals forming under higher supersaturation,leading to the stalagmite increased density.Stalagmite density fluctuation sensitively recorded stalagmite growth history and environment,demonstrating that stalagmite density can be used as a proxy for paleoclimatic research.
基金supported by the National Natural Science Foundation of China (Grants Nos. 41473009, 41273014, 40973007 & 40772110)
文摘We explored a time series of the Asian summer monsoon(ASM) variability during the transition period from the middle to the late Holocene in the marginal Asian monsoon region. We used an absolutely dated ^(230)Th record with only a ~20-year dating error, and oxygen isotope data with an 8-year average temporal resolution from the top 22-mm segment of stalagmite WXB07-4 from Wanxiang Cave, western Loess Plateau. The ASM intensity weakened gradually from 6420 to 4920 a BP, which was mainly characterized by three phases:(1) a strengthening phase with a higher precipitation amount between 6420 and 6170 a BP;(2) a smooth fluctuating interval during 6170–5700 a BP; and(3) a sudden extreme weakening period from 5700 to 4920 a BP. Interestingly, the extreme weakening interval of the ASM occurred during the period between 5700 and 4920 a BP, an abrupt change dated at 5430 a BP, which is known as the 5400 a BP, or 5.4 ka BP, event. The period included 290 years of gradual weakening, and 350 years of slow strengthening. This was synchronous with some cave records from the Asian monsoon region within dating errors. Comparing with Chinese archaeological archives over the past 7000 years, the early decline of the Yangshao Culture in the Yellow River Basin and the Hongshan Culture in the West Liao River Basin occurred during the period of gradual decrease of ASM precipitation. The dramatic decline in precipitation, caused by the extreme weakening of the ASM at 5400 a BP,may have been partly related to the decline of the Miaodigou Culture at the Yangguanzhai site in the Weihe River valley; the middle Yangshao Culture in western Henan in the Yellow River Basin; the early Dawenkou Culture on the lower reaches of the Yellow River; and the middle Hongshan Culture in the west of the Liaohe River valley. During the later period of the 5400 a BP event(5430–4920 a BP), a small amplitude increase and a subsequent sharp decrease of ASM precipitation may have also been linked to the contemporaneous prosperity and disappearance of the late Yangshao and Hongshan cultures; the disappearance of the late Yangshao Culture represented by the Yangguanzhai site in the Guanzhong basin on the Weihe River; the fourth phase of the late Yangshao Culture on the upstream Dadiwan site; the beginning of the middle Dawenkou Culture, the formation of its late stage,and the rise of the Longshan culture; and the rise of the Qujialing and Liangzhu cultures on the lower Yangtze River. Compared with the stalagmite precipitation records on the Qinghai-Tibetan Plateau, the rise and expansion of the Majiayao Culture in the upper Yellow River valley at 5300 a BP may have also been connected to the more dramatic increase of the summer monsoon precipitation at higher, rather than lower, altitudes during the late 5400 a BP event.
