Study On "Lake ¹⁴C Reservoir Effect" In Qinghai Lake And Xiligou Lake

The study of global change has special significance for revealing the operating mechanism of the Earth system,the laws of climate change and the influence of human on the Earth surface system.In the study of past global changes,we master the rules of the environment and climate change based on the study of the climate change of the Earth surface environment,so as to make the correct judgments for changes of the environment and climate in the future.The Qinghai-Tibet Plateau is a sensitive region which has a strong response to the global change,as a hot area in international research,it gains great attention with the problem of the global environmental climate becoming increasingly severe.There are plentiful brackish saline lakes on the Qinghai-Tibet plateau which record the abundant information of the environmental evolution in the past.¹⁴C Dating technology is a common method for the measurement of lacustrine sediments in the Qinghai-Tibet Plateau,however,due to the influence of"Lake ¹⁴C reservoir effect"?LRE?,there exists great differences in the environmental evolution records of different drills in the same lake.Taking Qinghai Lake?Brackish Lake?and Xiligou Lake?Salt Lake?as an example,the problem of LRE is systematically discussed in order to provide chronological basis for accurate reconstruction of the environmental evolution in northeast of the Qinghai-Tibet Plateau.We find that the LRE is different with different methods through summarizing the results of LRE research in Qinghai Lake area;The LRE is not identical in different position drillings with same method.In the same way,the LRE has difference in the geological history period.Considering that the LRE can be passed through the food chain,moreover,in some sites around Qinghai Lake,which preserves a large number of ¹⁴C dating materials such as naked carp bone,terrestrial animal bone,terrestrial plant charcoal and so on,thus,this paper tries to use the fish bone in the sites to obtain the LRE in different time and space of Qinghai Lake and explore the relationship of the LRE between fish bone and total organic carbon?TOC?recording.The 23 ¹⁴C ages?9 fish bones,5 bones,1 otolith,8 carbons?in the four sites or sections?GC,SLHQX,SNH and ND?around Qinghai Lake were selected,the conclusion as follow:the LRE in the fish bone of Qinghai Lake at 3 ka BP was 0.5 ka,the LRE in the otolith was 0.4 ka,the LRE of fish bone at 590yr BP was 0.6 ka and the LRE of modern fish bone may be 690±220 yr.The LRE in two modern algae samples are almost consistent,respectively are 1210±270 yr and1190±270 yr,the LRE of TOC and fish bone record are 1320±270 yr and 690±220 yr respectively,in summary,the LRE of fish bone is probably the smallest LRE of Qinghai Lake contemporarily.The three sites?GC,SLHQX and SNH?are contemporary site belongs to Kayue which is about 3100 cal BP,the LRE of fish bone records at three sites are almost identical,which are approximately 0.5 ka,illustrating that it has no significant difference in space of the LRE that fishbone recorded,which may reflect the overall LRE of Qinghai Lake,and the LRE of fish bone has great guiding significance for the correction of LRE of Qinghai Lake in later stage.There have been very few studies about Xiligou Lake in the past,in this paper,LRE is studied systematically for the first time.In April 2016,a sampling of the lake was carried out by using a gravity drill and a mud grab,altogether 5 cores were sampled and we selected a 80 cm long core to systematically study its chronology.The core is rich in ruppia seeds,meanwhile,plant residues are found on the surface and bottom,the ¹⁴C dating of TOC,seeds and plant residues at the same layer found that TOC has a higher LRE and the age results of ruppia seeds and plant residues have a good consistency.By using the difference values between the ruppia seeds and the TOC and then combining the linear extrapolation,we concluded that the LRE on the surface is 559±42a,at 40 cm,65cm and 75cm layer,the LRE is 609±42 a,731±42 a and 794±42 a respectively.