Climatic Variation Over The Past 570 Years Documented By Sediments From Kanas Lake,Altai Mountains,Northwestern China

Kanas Lake,in the Altai Mountains of Northwestern China,is surrounded by dense forests.The climate of the area is characterized by relatively abundant precipitation and cold temperatures.The understandings of the climate and environmental change history in this region are not only significant to the understanding of global climate change,but crucial to the sustainable development of the region as well.The study of high-resolution climate change in recent millennia has received wide attention is due to the profound impact of human on the environment and the rich research data.Because there is few meteorological station and short-term history of meteorological observation and scarce historical documents and in the region,although there are numerous tree-ring records,we need more abundant climatic proxies to provide us with much information of palaeoclimate and Palaeoenvironment to understand the climate change in this region deeply.Here a chronology was constructed from five AMS ¹⁴C dates from wood fragments?twigs?and it reveals that the 81-cm-long core spans the past 570 years.we present the results of stable carbon isotope analysis of a sequence of C3 terrestrial plant remains recovered from Kanas Lake.And also the results of grian size are used to reconstruct the hydraulic energy and depositional environments.The main conclusions are as follows.1.After correction for the atmospheric CO₂ concentration,the stable carbon isotope record provides a record of temperature changes over the last 570 years which can be clearly divided into the Little Ice Age and the Current Warm Period.The temperature increased continuously since the early 19th century and the 20^th century was the warmest period in the sequence.The temperature variations revealed in our study are consistent with temperature reconstructions from ice cores,tree-rings and from Teletskoe Lake in the Russian Altai,as well as with the extratropical NH mean temperature record.In addition,a trend of decreasing temperature is indicated by the decreasing stable carbon isotope ratios of both bulk plant remains and conifer needles in the upper part of the core,which corresponds with the widely-reported phenomenon of a hiatus in global warming and with meteorological data from the study region.2.The sensitive grain size component is identified in the sediment series using the grade-standard deviation method.Four end-members are decomposed by the Paterson end-member modelling algorithm based on grain-size data from core KNS15E in Kanas Lake,Altai Mountains.The results of EM2?EM3 and EM4 decomposed by the Paterson end-member modelling reflect the hydrodynamic conditions.EM4 represents the highest hydraulic energy and has a high average percentage during the period of 1450-1490 AD.EM3 represents a higher hydraulic energy and has the highest average percentage during the period of 1470-1800 AD and higher average percentage during the period of 1800-1950 AD.EM4 represents a lower hydraulic energy and has a high average percentage after 1800AD.The lowest hydraulic energy is in the period of CWP and before the Little Ice Age.The NAO and ENSO may play important roles in determining hydro-climatic variability on a multi-centennial time-scale.The study shows a cold and humid Little Ice Age over the past 570 years.