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High-resolution Stalagmite Records from Diaoshuihu Cave, Changchun, Northeast China for Late Holocene Paleoclimate and Environmental Reconstruction
stalagmite,stable isotope record,Late Holocene,AMS 14,
|Publication Year :||2019|
於長春市吊水壺洞採集的兩個石筍：DSH-1 (7公分)和DSH-2 (10公分)，分別在0.85公分和0.98公分左右的深度存在間斷，沉積間斷上方顏色較白較純；下半部由於石筍生長於洞內洪氾的淤泥之上，碳酸鈣純度不高，顏色褐黃。鈾釷定年困難，藉由210Pb定年與AMS碳十四定年建立石筍的年代模組。兩根石筍的210Pb定年均顯示頂部為現代沉積， 但DSH-2的210Pb定年結果較好，DSH-2頂部6mm為200年以內的沉積，沉積速率約為0.036mm/yr，AMS碳十四定年經死碳影響 (640年)的校正後，建立了約5300年的石筍年代模組。DSH-1的AMS 14C年代結果與DSH-2的基本相同，但死碳影響變化較大。
DSH-1和DSH-2分別做了486與698個穩定同位素分析，兩根石筍的穩定同位素結果有著相似的變化趨勢，指示為可用之氣候重建材料，並藉由兩根石筍穩同變化的峰谷點進行DSH-1的年代建立與校正。d18O、d13C與氣測資料及多種氣候指標(總太陽輻照-TSI、太平洋十年震盪指數-PDO、南方震盪指數-SOI)做對比，結果顯示d18O偏輕時對應於高降雨，反之亦反，指示主要反映降雨量效應，且d13C與d18O有相同的變化趨勢，指示氣候對於當地植被的影響。高雨量時期，d18O 偏輕，氣候濕潤，有利於植被生長，植被繁茂使d13C偏輕。d18O與總太陽輻照的對比結果可見d18O偏重時對應於較弱的太陽輻照，反之亦然。如在中世紀暖期、1800~1600 yr BP、以及2700~2400 yr BP，皆可見d18O與d13C偏輕(指示潮濕與植被良好時期)對應於較強的總太陽幅照；而在小冰期前期、3200~2800 yr BP，亦可見d18O與d13C偏重對應於較弱的總太陽輻照，尤其在約1300-1400 yr BP，石筍紀錄中d18O最重的時期，對應到總太陽輻照的最弱期。石筍紀錄中小冰期晚期因石筍沉積間斷而無紀錄，推測可能為當時氣候過於冷乾不利於石筍生長。d18O與PDO、SOI的比對結果中發現d18O偏輕時，對應於PDO的冷相位及反聖嬰時期，此兩時期時，西太平洋海溫較高，可從海洋帶來較多水氣。從水氣來源分析(NOAA HYSPLIT MODEL)結果中可見，氣測資料中的明顯乾期(AD2006)與濕期(AD1955)來自海洋的水氣有明顯不同，指示出研究區域的氣候，主要受太陽輻照的影響且水氣來源主要來自西北太平洋。
Located in North China, Changchun is near the north boundary of East Asian Summer Monsoon and shows quite different precipitation patterns on decadal scales from central and south China. Study of climatic variability and its forcing factors will be helpful for understanding of variation and forcing factors of entire East Asian Monsoon system.
Two stalagmites, DSH-1 (7-cm long) and DSH-2 (10-cm long), were collected from Diaoshuihu Cave (43o20’32”N, 125o50’35”E, 610 m a.s.l.) in southeast Changchun, Jilin, China. They grew on mud debris of an ancient groundwater flow channel inside the cave and contained significant detritus with yellowish color. The two stalagmites show a brief growth hiatus at 0.85-cm depth in DSH-1 and 0.98-cm depth in DSH-2. Above this hiatus, the stalagmites have lighter color and less detritus. 210Pb dating and 14C dating were used to determine the chronology of the stalagmites because of the difficulty of using U-Th dating. The 210Pb dating result indicates that both of the stalagmites have modern deposition, but DSH-2 has better dating result which has a clear exponential decay of excess 210Pb. The 14C dating results indicate that both stalagmites contain about 640 years of dead carbon influence. After removing this initial 14C age, the corrected 14C ages establish the chronology of DSH-2 which covers 5300-year climatic record. DSH-1 has similar 14C dating result but more variation of dead carbon influence.
The stalagmites were subsampled at 0.1~0.2 mm intervals for d18O and d13C analyses. A total of 486 subsamples from DSH-1 and 698 subsamples from DSH-2 for d18O and d13C analyses were made over the past 5300 years. The records of the two stalagmites exhibit similar stable isotopic patterns, demonstrating that they are good paleoclimate records. Based on the chronology determined by 210Pb dating and 14C dating, the stable isotope records compare with the local annual precipitation (AMP, 1905~2012), warm season precipitation (WSP, May to September), air temperature (T), Total Solar Irradiance (TSI), Pacific Decadal Oscillation (PDO) and El Niño-La Niña/Southern Oscillation (ENSO). The comparison between d18O and precipitation shows that lighter d18O corresponds to heavier rainfall. This indicates that d18O mainly reflects amount effect. The d13C record co-varies with d18O before 1910 C.E., reflecting that surface vegetation (shown by the d13C) above the cave was mainly influenced by wetness (reflected by the d18O). Comparison between d18O and TSI shows that heavier d18O corresponds to lower TSI; and vice versa. During periods of Medieval Warm Period (MWP), 1800~1600 yr BP, and 2700~2400 yr BP, lighter d18O and d13C which reflect wetter period and better vegetation coverage were corresponding to stronger TSI. Also, in the time intervals of early stage of Little Ice Age (LIA) and 3200~2800 yr BP, heavier d18O and d13C were corresponding to weaker TSI. An obvious dry climate and poor vegetation episode appeared between 1300 and 1400 yr BP in the DSH-2 record which corresponded to a significantly low TSI. Besides, the d18O record during late stage of Little Ice Age was absent due to the hiatus at 9.8-cm depth of DSH-2 stalagmite. This might be because the climate was so cold and dry that the stalagmite stopped to grow.
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