摘要
青藏高原作为地球“第三极”,对全球气候变化响应敏感。在季风与西风协同作用下,青藏高原在过去数千年中的年代际、百年时间尺度上存在南北相反的气候变化格局;但受限于青藏高原腹地缺少年代可靠的全新世高分辨率气候记录,千年时间尺度高原南北气候变化模态异同仍不明晰,更无从得知高原腹地湖泊及其流域的生态环境对气候变化的响应过程。本研究聚焦高原腹地沱沱河上游的开放湖泊班德湖(34.239°N,92.099°E;4583 m a.s.l),基于长115 cm的BDH19A沉积物岩芯的植物残体AMSC年代建立了可靠的年代框架,通过粒度、元素、矿物、自生碳酸盐及其碳、氧同位素、有机质含量和正构烷烃等多指标,重建了过去10 ka以来青藏高原中部的气候变化与生态环境响应过程。结果显示,青藏高原腹地在全新世以来表现出北半球夏季太阳辐射控制下夏季风降水逐渐减少的季风模式,导致流域和湖泊生产力持续降低,区域风沙活动整体增强。在千年时间尺度上,10~8.7 ka高原中部夏季风降水量最大,加之可能由于植物覆盖度较高,流域径流侵蚀减弱,风沙活动减少;7.7~5.2 ka和4~2 ka夏季风降水维持高值,入湖径流增加,促进流域和湖泊生物生产力提高,风沙活动受到抑制;相反,8.7~7.7 ka、5.2~4 ka和2 ka以来高原中部风沙活动的加剧是对亚洲夏季风快速衰退的响应,当前班德湖流域风沙环境是过去2 ka干旱风沙环境的延续与加剧。
As the“Third Pole”of the Earth,the Tibetan Plateau is sensitive to global climate change.Interactions between the Asian monsoon and the Westerlies systems control climatic and environmental changes in the Tibetan Plateau,resulting in an out-of-phase pattern of precipitation variation between the northern and the southern Tibetan Plateau on decadal to centurial time scales during the past several millenniums.However,it is not clear whether such an out-of-phase pattern of precipitation existed on a millennial time scale during the Holocene due to the lack of high resolution precipitation records with robust chronology from the northern Tibetan Plateau.In addition,it remains unknown how the ecosystem of a lake and the natural environment in its drainage basin response to climate change.In the present study,we focus on a 115-cm-long sedimentary core(BDH19A)collected from Lake Bande(34.239°N,92.099°E;4583 m a.s.l),an open lake in the upper reaches of Tuotuo River in the inner Tibetan Plateau where is located in an arid and semi-arid continental climate and surrounded by desert,alpine grassland and meadow.The reliable age model of the core was established by using AMSC dates from plant remains.Based on multiple proxies including grain size,XRF-based elements,minerals,carbon and oxygen isotopes of authigenic carbonate,organic matter content and n-alkanes from lacustrine sediments,the Holocene climate variations and their influences on the environment in the inner Tibetan Plateau during the past 10 ka(1 ka=1000 cal.a B.P.)were reconstructed.The results show that the oxygen isotope of authigenic carbonate,representing the summer monsoon precipitation,ranges from-10.70‰to-5.80‰,with an average of-9.03‰,and has been continuously positive since the Early Holocene,indicating that the precipitation gradually decreased during the Holocene.The percentage of sand in sediments increased rapidly from about 30%during the Early Holocene to over60%during the Late Holocene.In addition,the values of principal component 1,which represents the terrigenous mineral elements decreases periodically during the Holocene.The organic matter content ranges from 2.27%to7.08%(with an average of 4.18%)and the total concentration of n-alkanes ranges from 2.76μg/g to 21.83μg/g(with an average of 6.45μg/g).The carbonate content varies from 21.59%to 57.73%(with an average of36.70%),and its carbon isotope values change between 3.21‰to 7.50‰(with an average of 5.45‰).In summary,the terrestrial mineral elements content,carbonate content,carbon isotope of authigenic carbonate,organic matter content and total n-alkanes concentration decreased correspondingly during the Holocene.We also found that the inner Tibetan Plateau has experienced a gradually decreasing summer monsoon precipitation during the Holocene,which was triggered by the Northern Hemisphere summer insolation;the long-term decreasing precipitation has led to a continuous decline of productivity in the basin and the lake,and led to the overall increase of regional aeolian activities.On millennium timescales,summer monsoon precipitation was enhanced during 10.0~8.7 ka,resulting in decreased runoff erosion and weakened aeolian activities with a possible higher vegetation coverage.During the periods of 7.7~5.2 ka and 4~2 ka,the summer monsoon precipitation maintained at a high level and the runoff increased,promoting increased productivity and the inhibited aeolian activities.On the contrary,the intensification of aeolian activities were the response of the rapid decline of Asian summer monsoon during intervals of 8.7~7.7 ka,5.2~4.0 ka and 2~0 ka.We suggest that the modern aeolian environment in the drainage basin of Lake Bande is the continuation and intensification of the arid and aeolian environment during the past 2 ka.
作者
李友谟
吴铎
袁子杰
陈林
陈雪梅
周爱锋
LI Youmo;WU Duo;YUAN Zijie;CHEN Lin;CHEN Xuemei;ZHOU Aifeng(Key Laboratory of Western China's Environmental Systems,Ministry of Education,College of Earth and Environmental Sciences,Lanzhou University,Lanzhou 730000,Gansu;Northwest Institute of Eco-Environment and Resources,Chinese Academy of Science,Lanzhou 730000,Gansu)
出处
《第四纪研究》
CAS
CSCD
北大核心
2022年第5期1328-1348,共21页
Quaternary Sciences
基金
国家自然科学基金项目(批准号:41807442和42171150)
科技部第二次青藏高原综合科学考察研究项目(批准号:2019QZKK0601)共同资助。
关键词
青藏高原
班德湖
亚洲夏季风
全新世
生态环境响应
Tibetan Plateau
Lake Bande
Asian summer monsoon
Holocene
ecological environment response
