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
位于青藏高原与黄土高原过渡带的甘肃武都万象洞石笋WXSM51和WXSM52提供了M IS 5(118~79kaB.P.)高分辨率的1δ8O记录。研究表明,万象洞石笋1δ8O值与夏季风强度呈负相关关系,与我国西南部的贵州董歌洞石笋1δ8O记录有良好的对应关系,并...位于青藏高原与黄土高原过渡带的甘肃武都万象洞石笋WXSM51和WXSM52提供了M IS 5(118~79kaB.P.)高分辨率的1δ8O记录。研究表明,万象洞石笋1δ8O值与夏季风强度呈负相关关系,与我国西南部的贵州董歌洞石笋1δ8O记录有良好的对应关系,并与高纬度的格陵兰NGR IP冰芯1δ8O记录和65°N太阳辐射强度有很好的一致性,说明万象洞石笋1δ8O记录了118~79kaB.P.期间亚洲季风强度的变化,同时也说明东亚季风强度的变化和全球气候变化同步,而且主要受控于北半球太阳辐射强度的变化。同时它与地中海碳酸盐记录有很好的相似性,和巴西石笋1δ8O记录在千年尺度上表现出相反的变化趋势,说明东亚季风区、地中海地区以及巴西季风区之间存在密切的联系,指示了南北半球气候在千年尺度上存在“跷跷板”(seesaw)现象。万象洞石笋1δ8O记录的M IS 5b与M IS 5 a突发性转换,与NGR IP冰芯1δ8O记录相似,而与神农架记录存在差异,说明万象洞地区对亚洲季风强度的响应更为敏感。展开更多
The Marine Isotope Stage(MIS5e)is characterized by a warmer climate than that of the pre-industrial period,and serves as an analog for the Current Warm Period(CWP).However,uncertainties persist regarding its climatic ...The Marine Isotope Stage(MIS5e)is characterized by a warmer climate than that of the pre-industrial period,and serves as an analog for the Current Warm Period(CWP).However,uncertainties persist regarding its climatic stability.Here,we retrieved a stalagmite(WXB075)from Wanxiang Cave in the eastern Qinghai-Tibetan Plateau,and employed abs-olute^(230)Th dating and relative annual layer data to establish a high-precision chronological framework for reconstructing the history of the Asian summer monsoon(ASM)and environmental evolution during early MIS5e with multiple proxies.The findings indicate that the annually laminated stalagmite was formed during Cooling Event 27(C27).The deposition of WXB075 experienced a hiatus(~125.58 ka BP)due to a significant cooling event in the North Atlantic,which may be linked to the unstable climate in the Northern Hemisphere.Additionally,the impact of meltwater discharge in high northern latitudes results in a two-phase evolution of the ASM,i.e.,an initial weaker stage followed by a gradual increase(with exception of deposition hiatus).The climatic instability of ASM is generally characterized by a quasi-60 year cycle that affects vegetation conditions,biological productivity,and karst hydroclimate dynamics.However,the increase in meltwater and decrease in temperature in the Northern Hemisphere have led to a weakened ASM and subsequent reduction in precipitation.Consequently,vegetation degradation above the cave has occurred along with a slowdown of karst hydroclimate.The vegetation conditions,organic matter content,and wet/drought of the karst hydroclimate were affected by both the large-scale monsoon circulation and local environment during extreme weakening(strengthening)of the monsoon when high-frequency climatic events of ASM occurred.A comparison ofδ^(18)O records between early MIS5e and the past 2000 years reveals that the climate during early MIS5e differed significantly from that of CWP,Medieval Warm Period(MWP),and Dark Age Cold Period(DACP)but was similar to Little Ice Age(LIA).Comparison with other geological records from the Northern Hemisphere indicates that climate instability was a widespread phenomenon during MIS5e.The power spectrum analysis of WXB075δ^(18)O reveals significant quasi-60 and 35 a cycles during the early MIS5e,which is consistent with the Atlantic Multidecadal Oscillation(AMO).The comprehensive results demonstrate that the ASM in the early MIS5e was closely linked to solar activity,Intertropical Convergence Zone(ITCZ)position,and Atlantic Meridional Overturning Circulation(AMOC).展开更多
Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave,Wudu,Gansu,variation of monsoonal precipita-tion in the moder...Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave,Wudu,Gansu,variation of monsoonal precipita-tion in the modern Asian Monsoon (AM) marginal zone over the past 100 years was reconstructed. Comparison of the speleothem δ18O record with instrumental precipitation data at Wudu in the past 50 years indicates a high parallelism between the two curves,suggesting that the speleothem δ18O is a good proxy for the AM strength and associated precipitation,controlled by "amount effect" of the pre-cipitation. Variation of the monsoonal precipitation during the past 100 years can be divided into three stages,increasing from AD 1875 to 1900,then decreasing from AD 1901 to 1946,and increasing again thereafter. This variation is quite similar to that of the Drought/Flooding index archived from Chinese historical documents. This speleothem-derived AM record shows a close association with the Pacific Decadal Oscillation (PDO) between AD 1875 and 1977,with higher monsoonal precipitation corre-sponding to cold PDO phase and vice versa at decadal timescale. The monsoonal precipitation varia-tion is out of phase with the PDO after AD 1977,probably resulting from the decadal climate jump in the north Pacific occurring at around AD 1976/77. These results demonstrate a strong linkage between the AM and associated precipitation and the Pacific Ocean via ocean/atmosphere interaction. This rela-tionship will aid to forecast future hydrological cycle for the AM monsoon region,and to improve forecasting potential of climatic model with observation data from cave.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.
文摘位于青藏高原与黄土高原过渡带的甘肃武都万象洞石笋WXSM51和WXSM52提供了M IS 5(118~79kaB.P.)高分辨率的1δ8O记录。研究表明,万象洞石笋1δ8O值与夏季风强度呈负相关关系,与我国西南部的贵州董歌洞石笋1δ8O记录有良好的对应关系,并与高纬度的格陵兰NGR IP冰芯1δ8O记录和65°N太阳辐射强度有很好的一致性,说明万象洞石笋1δ8O记录了118~79kaB.P.期间亚洲季风强度的变化,同时也说明东亚季风强度的变化和全球气候变化同步,而且主要受控于北半球太阳辐射强度的变化。同时它与地中海碳酸盐记录有很好的相似性,和巴西石笋1δ8O记录在千年尺度上表现出相反的变化趋势,说明东亚季风区、地中海地区以及巴西季风区之间存在密切的联系,指示了南北半球气候在千年尺度上存在“跷跷板”(seesaw)现象。万象洞石笋1δ8O记录的M IS 5b与M IS 5 a突发性转换,与NGR IP冰芯1δ8O记录相似,而与神农架记录存在差异,说明万象洞地区对亚洲季风强度的响应更为敏感。
基金supported by the National Natural Science Foundation of China(Grant Nos.41873001&41473009)。
文摘The Marine Isotope Stage(MIS5e)is characterized by a warmer climate than that of the pre-industrial period,and serves as an analog for the Current Warm Period(CWP).However,uncertainties persist regarding its climatic stability.Here,we retrieved a stalagmite(WXB075)from Wanxiang Cave in the eastern Qinghai-Tibetan Plateau,and employed abs-olute^(230)Th dating and relative annual layer data to establish a high-precision chronological framework for reconstructing the history of the Asian summer monsoon(ASM)and environmental evolution during early MIS5e with multiple proxies.The findings indicate that the annually laminated stalagmite was formed during Cooling Event 27(C27).The deposition of WXB075 experienced a hiatus(~125.58 ka BP)due to a significant cooling event in the North Atlantic,which may be linked to the unstable climate in the Northern Hemisphere.Additionally,the impact of meltwater discharge in high northern latitudes results in a two-phase evolution of the ASM,i.e.,an initial weaker stage followed by a gradual increase(with exception of deposition hiatus).The climatic instability of ASM is generally characterized by a quasi-60 year cycle that affects vegetation conditions,biological productivity,and karst hydroclimate dynamics.However,the increase in meltwater and decrease in temperature in the Northern Hemisphere have led to a weakened ASM and subsequent reduction in precipitation.Consequently,vegetation degradation above the cave has occurred along with a slowdown of karst hydroclimate.The vegetation conditions,organic matter content,and wet/drought of the karst hydroclimate were affected by both the large-scale monsoon circulation and local environment during extreme weakening(strengthening)of the monsoon when high-frequency climatic events of ASM occurred.A comparison ofδ^(18)O records between early MIS5e and the past 2000 years reveals that the climate during early MIS5e differed significantly from that of CWP,Medieval Warm Period(MWP),and Dark Age Cold Period(DACP)but was similar to Little Ice Age(LIA).Comparison with other geological records from the Northern Hemisphere indicates that climate instability was a widespread phenomenon during MIS5e.The power spectrum analysis of WXB075δ^(18)O reveals significant quasi-60 and 35 a cycles during the early MIS5e,which is consistent with the Atlantic Multidecadal Oscillation(AMO).The comprehensive results demonstrate that the ASM in the early MIS5e was closely linked to solar activity,Intertropical Convergence Zone(ITCZ)position,and Atlantic Meridional Overturning Circulation(AMOC).
基金the National Natural Science Foundation of China (NSFC) (Grant No.40471137)the Innovation Team Project of the NSFC (Grant No.40421101)Doctor Station Foundation,Ministry of Education of China (Grant No.20040730025)
文摘Based on 5 high-precision 230Th dates and 103 stable oxygen isotope ratios (δ18O) obtained from the top 16 mm of a stalagmite collected from Wanxiang Cave,Wudu,Gansu,variation of monsoonal precipita-tion in the modern Asian Monsoon (AM) marginal zone over the past 100 years was reconstructed. Comparison of the speleothem δ18O record with instrumental precipitation data at Wudu in the past 50 years indicates a high parallelism between the two curves,suggesting that the speleothem δ18O is a good proxy for the AM strength and associated precipitation,controlled by "amount effect" of the pre-cipitation. Variation of the monsoonal precipitation during the past 100 years can be divided into three stages,increasing from AD 1875 to 1900,then decreasing from AD 1901 to 1946,and increasing again thereafter. This variation is quite similar to that of the Drought/Flooding index archived from Chinese historical documents. This speleothem-derived AM record shows a close association with the Pacific Decadal Oscillation (PDO) between AD 1875 and 1977,with higher monsoonal precipitation corre-sponding to cold PDO phase and vice versa at decadal timescale. The monsoonal precipitation varia-tion is out of phase with the PDO after AD 1977,probably resulting from the decadal climate jump in the north Pacific occurring at around AD 1976/77. These results demonstrate a strong linkage between the AM and associated precipitation and the Pacific Ocean via ocean/atmosphere interaction. This rela-tionship will aid to forecast future hydrological cycle for the AM monsoon region,and to improve forecasting potential of climatic model with observation data from cave.
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.
