利用高解析度石筍紀錄重建中國東北晚全新世以來的古氣候和植被變化：吉林省無名洞石筍S1S

Abstract

本研究使用的材料為一根採自中國東北地區通化市無名洞長度8.7公分的石筍（取名為S1S），研究目的是希望藉由高解析度的石筍紀錄找尋驅動中國東北地區氣候變化的因子。 由於S1S所含的鈾含量太少且初始釷含量過高，導致鈾釷定年無法為S1S提供良好的年代結果，因此本研究需另尋其他方法為S1S建立合理的年代模式；根據表層核爆碳的信號以及Pb-210定年所表現的衰變趨勢，清楚地了解到S1S表層為現代沉積（晚於AD 1950），再藉由12個14C定年的結果可知S1S涵蓋近2500年。雖然死碳效應存在於石筍當中，進而影響碳十四定年的最終結果，但本研究基於固定S1S沉積速率的方法成功回推整根石筍的年代。 本研究同時分析873個穩定同位素樣品，將S1S的δ18O 和δ13C曲線與近代2500年的太陽總輻照度（TSI）進行對比，發現當太陽總輻照度較弱時大致對應δ18O和δ13C偏重的情形，推測關係為：當太陽總輻照度較弱，導致海陸的溫差減小，東亞夏季風（EASM）強度減弱，中國東北地區降雨量減少，又因為在百年尺度的東亞石筍δ18O紀錄主要反映雨量效應，造成石筍δ18O偏重；另外，雨量的減少又會使當地植被發育較差且C3/C4植物比例下降，造成δ13C的偏重。 對S1S的δ18O和δ13C曲線進行功率譜分析能觀察到中國降水以及太陽百年活動的週期性（如：Suess cycle），再次說明S1S的δ18O和δ13C紀錄足以還原晚全新世以來中國東北的古氣候。在近1500年以來，S1S的δ18O在AD 820〜920、1040〜1120、1280〜1350、1450〜1570、1900〜現在這幾個時期普遍偏重，或可代表當時中國東北地區氣候較為乾燥。另外，本研究對比了S1S紀錄與石花洞、萬象洞、董哥洞及和尚洞的石筍紀錄、花粉紀錄、韓國乾指數和中國北方的乾濕指數等，討論區域氣候的關係。

A 8.7-cm long stalagmite （S1S） from Unnamed Cave （41.82oN, 126.15oE） located at Tonghua City has been studied for understanding forcing factors of the climate in Northeast China. Owing to low U contents, 230Th/U dating on the stalagmite was not successful. According to AMS 14C and 210Pb dating results, Stalagmite S1S covers a positional record of the past 2500 years with the modern surface （after 1950 AD）. Although dead carbon influence （DCI） affects the AMS 14C dating results, we adopted appropriate method to get the age sequence of S1S. 873 subsamples from S1S were measured δ18O and δ13C. Comparison of the δ18O record of S1S with the Total Solar Irradiance （TSI） records exhibits negative correlations - When TSI is lower, the δ18O is heavier; and vice versa. We interpret that the temperature difference between continent and ocean is decreasing when TSI is low, leading EASM intensity to be weaker. Then, the water vapor transported from western Pacific Ocean to Northeast China is less, resulting heavier δ18O value （dominated by amount effect）. On the other hand, due to low precipitation, vegetation coverage is sparse under dry climates, resulting heavier δ13C trend. Furthermore, both power spectral and wavelet analyses of the δ18O record of S1S show clearly a 202-year cycle, which is one of the most famous cycle of solar activity, named “Suess cycle” as known as “de Vries cycle”. This study also compared S1S with many records such as other stalagmite records, pollen records, drought index in Korea and DWI in NC and so on. This study indicates that the S1S record not only helps us to reconstruct the climate change during the past 2500 years in Northeastern China, but also illustrate the controlling factors such as TSI of the regional climate.