Application of automatic annual layer identification method in ice core dating on the Qinghai-Xizang Plateau
Ice cores are an effective proxy for past climate changes,and high-resolution reconstruction necessi-tates precise dating methods. This study combines manual dating with an automated layer recognition algorithm (StratiCounter) based on a Hidden Markov Model (HMM) framework to test,validate,and analyse the perfor-mance of the algorithm in assisting the dating of Zuoqiupu,Dasuopu,and Anemaqen ice cores. The method re-duces the time required for manual layer-by-layer identification during binding reference layers,synchronizing with other ice core records,and reviewing processes by automatically inferring layer positions and providing er-ror ranges. Initially,a collection of fundamental dating templates and layer constraint points are manually pro-vided. Next,the algorithm familiarises itself with the template for calculating the quasi periodic cycle of the ice core proxy variable. It then identifies the target paragraph and examines the presence of layer constraints. Per-form a comprehensive search for potential points while considering layer constraints,and employ the maximum likelihood method to determine the most suitable solution from the available options. The findings show that for the upper sections of the Zuoqiupu and Dasuopu ice cores,the algorithm-assisted dating results have an accumu-lated error of less than 2 years (3％) when compared to known chronologies,indicating a high level of consisten-cy. Even under simulated sample loss conditions and the absence of tie points,the algorithm remains operation-al,resulting in a cumulative error of less than five years. Further analysis of the upper section of the Anemaqen ice core reveals 1 to 2 year differences between algorithmic and manual dating results at specific sections e1[2.07,4.47]and e2[8.31,9.71]. After using pollution layer data,the ice core at 56.48 metres was dated to 74 years with an error range of±3 years. Integrating reference layer findings like β-activity and 137Cs with δ18O counting layers helped determine the age sequence of the upper 0.05～56.48 m of the Anemaqen Ice Core,from 1947 to 2020 AD. The method combines the advantages of manual dating with the standardised hierarchical rec-ognition capability of algorithms,thereby reducing the need for manual intervention in the age correction pro-cess. It also quantifies potential dating errors and,to some extent,improves the dating procedure.
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