The Organic Carbon-based AMS¹⁴C Chronological Study For Late Holocene Lake Sediments Of Lake Toson In Qaidam Basin

The radiocarbon dating is the most commonly used method for lake sediments,while the bulk organic matter is usually chosen as dating material when there are none terrestrial plants in lake sediment,and TOC 14 C reservoir effect is the prerequisite and basis for the establishment of the lake sediment chronological sequence.In this dissertation,a high-density of TOC AMS-14 C dating had been done for the 3.81m-long core in Toson Lake(TSLA),and the 14 C reservoir effect was evaluated by the intercept method to establish chronological sequence since late Holocene,providing the basis for the discussion of high-resolution climatic evolution in this region.The 14 C ages of modern watershed water DIC(Dissolved Inorganic Carbon)and watershed surface sediments indicate the modern reservoir effect is complex in spatial distribution,with different reservoir effects at different locations in the Toson Lake.The input of organic debris from the watershed surface sediment,which contains old carbon,is the main factor of reservoir effect in organic dating result of core TSLA.The average reservoir effect of core TSLA was 1650 years using the intercept method for 19 TOC 14 C ages.Combined with the distribution characteristics of age-depth relationship,old group A2 and young group A1 might share the same sediment rate when their regression curves paralleled,but their intercepts represented different reservoir effects,2086 and 1520 years respectively.However,the reversed and unusually old 14 C years,outside the age-depth relationship,contained more old carbon.After deducting the reservoir effects,the common three modeling programs(Oxcal?Clam and Bacon)were applied separately to calibrate the 14 C ages and establish the age-depth models.Comparing the changes of the inorganic carbon isotope(?18Ocarb)of the core TSLA and the core GHB in Gahai,where it had been established the accurate chronology in core GHB,the results indicated that Bacon modeling program could better reflect deposition pattern of Toson Lake and also proved that the evaluation of reservoir effect in TOC 14 C ages since late Holocene was reasonable.Based on the age-depth model from Bacon modeling program,the core TSLA covered the past 4633 years and provided chronological basis for reconstructing the environmental changes since late Holocene with core TSLA.