Evolution of climate in the Jianghan Plain:evidence from elemental geochemical records of lacustrine sediments since 12.8 cal.ka BP
Background,aim,and scope The Jianghan Plain is a typical flood plain composed of inter-river depressions,with alternating fluvial and lacustrine sediments that are sensitive to climate change and contain a large amount of paleoclimate information.Therefore,it is an ideal place to study paleoclimate.Previous studies have mostly concentrated on magnetic susceptibility,particle size,and pollen assemblages.However,it is insufficient to reconstruct the climatic and environmental evolution of Jianghan Plain from the end of the deglacial to the Holocene through the combination of regular trace elements in lacustrine sediments and geochemical analysis methods on a longer time scale.Based on the analysis of lacustrine sedimentary geochemical elements,we aimed to reconstruct the climatic and environmental evolution of the Jianghan Plain from the end of the deglacial to the Holocene and discuss the possible driving factors of this change.Materials and methods A lacustrine sedimentary section(numbered JZ-2010)in Jingzhou,with a thickness of 637 cm was selected for sampling,which was composed of silty clay rich in organic matter.Furthermore,only the lacustrine sedimentary section in the middle and lower parts was sampled,and that in the upper part was not discussed due to flood disturbances.The lacustrine sedimentary section in the middle and lower parts was further subdivided into nine layers,and 206 samples were collected from bottom to top at 2 cm intervals.X-ray fluorescence spectroscopy(XRF)was used to determine the composition of geochemical elements.To establish the sedimentary chronosequence,six samples were collected from the middle and lower parts of the section for accelerator mass spectrometry radiocarbon(AMS 14C)dating.The samples ware jointly performed by the AMS 14C Sample Preparation Laboratory of Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,and the State Key Laboratory of Nuclear Physics and Technology,Peking University.Results The results showed that from 12.8 to 9.1 cal.ka BP,the climate of the study area was generally cool and dry,with a trend of gradually changing to warm and humid.From 9.1 to 6.3 cal.ka BP,the climate was warm and humid,which should be the beginning of the Holocene Optimum.From 6.3 to 4.4 cal.ka BP,the environmental proxies changed obviously,indicating unstable environmental fluctuations in the early stage,and there was a trend that the climate changed to drought gradually.From 4.4 to 1.3 cal.ka BP,the climate gradually changed to warm and humid after the 4.2 ka cold-dry event.Discussion We found a significant relationship between SiO2/Al2O3 ratios,chemical index of alteration(CIA),Rb/Sr ratios,solar radiation,a record of hematite-stained particles in North Atlantic,and δ13C of benthic foraminifera shells,revealing that the climate change in the Jianghan Plain since 12.8 cal.ka BP has been driven by the variation of North Atlantic Deep Water(NADW).The millennial cold-dry event might have established an ocean-atmosphere linkage mechanism affecting climate change with the Atlantic through the low-latitude Pacific and its upper atmosphere.At the same time,the trend of climate change was consistent with the reduction of the northern hemisphere summer solar radiation since the Middle and Late Holocene,and the solar radiation indirectly affected regional climate change mainly through monsoon circulation.In addition,the climate in the Jianghan Plain was strongly suppressed by the Laurentide Ice Sheet in the high latitude of the northern hemisphere,resulting in a more severe climate during the Early Holocene.Conclusions The five environmental proxies of Ti,CIA,Rb/Sr,SiO2/Al2O3,and SiO2/Fe2O3 ratios in the JZ-2010 section of the Jianghan Plain significantly recorded the abrupt climate events,such as YD,9.5 ka BP,5.3 ka BP,and 4.2 ka BP events,while there was no obvious record of the 8.2 ka BP event.By comparing the solar radiation record,the North Atlantic hematite staining particles and benthic δ13C records with the variation characteristics of environmental indicators in the Jianghan Plain,we found that solar radiation might be one of the main driving factors of the millennial-scale climate change in the Middle and Late Holocene.There was a certain correlation between the NADW,North Atlantic drift ice events,and SiO2/Al2O3,Rb/Sr,and CIA,indicating that the air-sea coupling process would cause regional climate change by influencing the atmospheric circulation model.Therefore,in the Jianghan Plain,the Early Holocene climate change was dominated by NADW,and the Middle and Late Holocene climate change was driven by NADW and the northern hemisphere solar radiation.Recommendations and perspectives The results of this study provide possible driving mechanism of climate change in the Jianghan Plain.Furthermore,more research should be conducted to deepen understanding of the possible driving factors of paleoenvironmental evolution from the end of the last deglaciation to the Holocene.
万方数据
