[A-CC37] [EJ] アイスコアと古環境変動

[ACC37-P04] Seasonal scale dating of a shallow ice core from Greenland using oxygen isotope matching between data and simulation

古川 崚人¹、*植村 立²、藤田 耕史³、Sjolte Jesper⁴、芳村 圭⁵、的場 澄人¹、飯塚 芳徳¹ (1.北海道大学低温科学研究所、2.琉球大学理学部、3.名古屋大学環境学研究科、4.ルンド大学第四紀地質学教室、5.東京大学生産技術研究所)

キーワード：Greenland, ice core, seasonal scale dating, oxygen isotope, air temperature, annual accumulation rate

A precise age scale based on annual layer counting is essential for investigating past environmental changes from ice core records. However, the uncertain seasonal cycle (i.e., non-sinusoidal pattern) of oxygen isotope (δ¹⁸O) records causes inevitable errors in the dating. Here, we propose a dating method based on matching the δ¹⁸O variations between ice-core records and records simulated by isotope-enabled climate models. We applied this method to a new δ¹⁸O record from an ice core obtained from a dome site in southeast Greenland. The close similarity between the δ¹⁸O records from the ice core and models enabled correlation and the production of a precise age scale, whose accuracy was ±2 months. A missing δ¹⁸O minimum in the 1995/1996 winter is an example of the uncertain δ¹⁸O seasonal cycle, which hampers annual layer counting. Our analysis suggests that the missing δ¹⁸O minimum was likely caused by a combination of warm air temperature, weak moisture transport, and cool ocean temperature. Based on the age scale, the average accumulation rate from 1960 to 2014 was reconstructed as 1.02 m yr^-1. The annual accumulation rate increases with a slope of 3.6 (mm year^-1), which is mainly caused by the increase in the autumn accumulation rate (2.6 mm year^-1), which is likely linked to the enhanced hydrological cycle caused by the decrease in Arctic sea ice area. On a seasonal time-scale, our reconstructed accumulation suggests that the ERA re-analysis data overestimates the seasonality in this southeast dome region.