The Influence Factors And Evalution Of ¹⁴C Reservoir Effects Of Lakes In The Western China

Numerous lakes in the western China are excellent media for studying environmentchange.The establishment of age in the lake sediment profile mainly depends on the AMS ¹⁴C dating technique However,the most of the lakes have the presence of ¹⁴C lake reservoir effects?LREs?,especially in dry and cold areas with a meager plant cover in the west China lakes.The presence of LREs is often hampered by using radiocarbon dating of lake sediments in the palaeoenvironmental and climate research.In recent years,the lakes of western China became a hotspot of the palaeoenvironmental and climate researchers and the assessment of influence factors and spatial patterns of LREs is crucial,especially the evaluation of modern LREs is a key prerequisite for the organization of reliable radiocarbon age-depth relationships for lake sediment cores.Hence,in this paper we selected research points related to the lake surface sediments?LSSs?in the western China?2 Xinjiang freshwater lakes,3 Hoh Xil area lakes,and 12 northern Tibet lakes?to investigate the radiocarbon chronology and LREs.Based on 28 samples of LSSs and three plant residues,which are collected from the western region?17 lakes?discussed the differences in the spatial and temporal of the LREs.28 samples and three plant residues were dated by the AMS ¹⁴C dating approach.The water chemistry and sediment geochemistry of the lakes were analyzed.By summarizing and analyzing the lake reservoir ages?RAs?,water chemistry and sediment geochemistry in the western China lakes,which exhibited the distribution characteristics of the LREs and the main influence factors.Furthermore,we evaluated the merits and demerits of modern calibration approach in LSS.This paper mainly obtained the following conclusions:?1?The RAs of Lake Bosten have been focused on 670 to 945 a,and the maximum age is up to 3535 a,the minimum age is present-day.The RAs of Lake Ulungur centered on from 85 to365 a,and the maximum age is up to 415 a,the minimum age is present-day.This investigation works the spatial variability of LREs within single lakes,through an argument of new data for Lake Ulungur,Lake Bosten and Lake Heihai,as well as the previously published data for other individual lakes.The LREs for Lake Ulungur,Lake Bosten and Lake Heihai on the Xinjiang and Hoh Xil region were determined for LSSs collected to locate different sites.Relatively larger LREs in the margins of lakes,lower and more stable LREs towards the central region owing to more authigenic carbonate rocks in lake,and higher LREs in river-lake confluence and wetland are a common pattern due to more exogenous carbonate rocks within lake.Meanwhile,more complicated LREs were affected by the human activity.The influence of groundwater due to the dissolution of carbonaceous basement rock has higher LREs.The tectonically active lake catchment of Lake Kusai and xz-51 recorded larger LREs,which speculated that rising crustal old CO₂,HCO₃^-and CO₃^2-.Total organic matter contents?TOCs?in the central regions were contributed by endogenesis aquatic plants,and TOCs in the margins were mainly derived from endogenesis aquatic plants and exogenous plants,and the margin W-1 of Lake Ulungur contains lesser LREs.In addition,as a result of nuclear bomb testing,the ¹⁴C level of the atmosphere was elevated.LSSs of the slow sediment accumulation rates have a significantly impact on LREs.13.5-27.0 a for Lake Ulungur of accumulation age,which indicates F¹⁴C drop is the range of5%-10%for a sample in the study caused an uncertainty in LRE determination of 300-600 year.Therefore,this is another one reason why the lower LRE of Lake Ulungur than Lake Bosten.?2?The maximum age is up to 7750 a,and the minimum age is present-day in the Tibet Lake.The RAs of salt lake have been focused on 505 to 5995 a,and the older age is up to 7185 a,the younger age is 215 a.The RAs of freshwater lakes lake centered on 90 to 670 a,whereas the maximum age is 2110 a,and the minimum age is present-day.The large lakes have been focused on 905 to 7185 a,whereas the maximum age is up to 3535 a,as well as the minimum age is 670 a.The ages of the pool are 2110 a and 215 a.The older age of plant residues is 85 a,the other ages of plant residues are present-day.This discussion of 17 lakes in the western China indicates that the positive correlation between LREs and water chemistry(i.e.HCO₃^-and CO₃^2-),whereas the no significant correlation between LREs and pH,Ca²⁺.However,a pool of xz-23 has low water chmestry index,while the LRE is strong?2110 a?,which infer the pool was influned by weathering the carbonaceous basement rocks.The higher the salinity,the greater the LREs.The investigation of lakes basement rock exhibits carbonaceous rocks are crucial influence factors for LREs.Geochemistry study shows the research region is strong weathering intensity.Quartz and feldspar is main mineral in lakes.Then,higher clay and carbonate mineral contents in the north Tibet and Hoh Xil area,as well as larger carbonate mineral contents in Lake Bosten are common pattern.There are the obvious correlation between the weathering intensity?CIA,CIW and PIA?and LREs in north Tibet,Hoh Xil region lakes and Lake Bosten.The xz-51 sample of hydrothermal sediment has the lower CIA,CIW and PIA,which suggested that rising CO₂,HCO₃^-and CO₃^2-further contributes to the LREs in the pool.Though analyzing?¹³C,?¹⁸O,?¹³C_org,TOCs and C/N ratios for lakes in western China in this paper,the results suggested that the TOCs are derived from endogenesis aquatic plants,mainly consist of phytoplankton,diatoms,aquatic plants,aquatic plants+terrestrial plants,and less terrestrial plants.?3?This paper analyzed the LREs using the LSSs,determined the presence of LRE in the studied lakes,examined their temporal patterns as well as assessed the imposed chronological uncertainties.The lake RAs vary from present-day carbon to 24400 a,which have been focused on1000 a to 2000 a,and the maximum age is up to 24400 a.The study infers the spatial variability of LREs in individual lake,which ¹⁴C RA errors of Lake Qinghai and Lake Genggahai are 2810 a and 6540 a,respectively.Thus,using these ages corrected LRE need to be careful.However,partial lakes can be utilized to correct LRE,i.e.Lake Heihai,Lake Bosten,Lake Ulungur and Lake Dangyongco.This study also shows carbonate materials for dating are affected by LRE significantly.We compile the published ¹⁴C RAs to use other LREs calibration approach,and the lake RAs vary from 90 a?Lake Manas?to 6670 a?Lake Bangong Co?,they are centered on from1000 a to 3000 a,the maximum lake RA is up to 6670 a.Meanwhile,the study reveals the lakes of carbonaceous basement rocks have strong impact on the LREs.?4?The discussion of modern LREs calibration approach show that the AMS ¹⁴C of LSS can obtain the present-day LREs,whereas the result was significantly influenced by these different components and hard-water effect.Therefore,present-day LREs calibration approach of LSS is not positive way for correcting LREs.However,if there are materials?i.e.plant or animal residues,sporopollen,charcoal,et al.?in lake sediments,it will be extremely useful approach.Meanwhile,we are utilized other dating(i.e.OSL,²¹⁰Pb and ¹³⁷Cs,et al.).