Trend of increasing Holocene summer precipitation in arid central Asia: Evidence from an organic carbon isotopic record from the LJW10 loess section in Xinjiang, NW China
Trend of increasing Holocene summer precipitation in arid central Asia: Evidence from an organic carbon isotopic record from the LJW10 loess section in Xinjiang, NW China
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DOI：
10.1016/j.palaeo.2018.04.006
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发表时间：
2018-11
期刊：
影响因子：
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通讯作者：
Haichao Xie;Huiwen Zhang;J. Ma;Guoqiang Li;Qiang Wang;Z. Rao;Wei Huang;Xiao-zhong Huang;Fahu Chen
中科院分区：
文献类型：
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作者：
Haichao Xie;Huiwen Zhang;J. Ma;Guoqiang Li;Qiang Wang;Z. Rao;Wei Huang;Xiao-zhong Huang;Fahu Chen
由于缺乏可靠的气候指标，全新世“西风为主”的中亚干旱地区降水变化一直存在争议。本文对新疆天山北麓陆角湾10剖面的大量样品进行了高分辨率（约100 年/个）的有机碳同位素（δ13Corg）记录。钾长石pIRIR测年提供了一个可靠的年表。在全新世早中期，12 ka ~ 6 ka（1 ka = 1000 年前），δ 13corg值相对稳定，平均在- 22.5‰左右。在6 ka后，δ 13corgvalue整体呈负变化趋势，负值最大的为- 25.2‰，出现在剖面的最上端，处于全新世成土区间。现代气候变量与该地区表层土壤δ 13corg值的关系研究表明，表层土壤δ 13corg值与夏季降水（6 ~ 8月）呈显著负相关。因此，我们采用夏季降水量与表层土壤δ 13corg之间的定标模型，定量重建研究区全新世夏季降水历史。结果表明：全新世早期至中期（12-6 ka）是该区夏季降水最少的时期（约85 mm）；6 ka以后，降水持续增加，目前约为137 mm /年。我们的重建结果与气候模拟结果和区域有效湿度记录基本一致。因此，我们得出结论，夏季降水最多，因此最潮湿的气候发生在全新世晚期。北半球夏季日照的减少可能导致了CGT（环全球遥相关）由正向负的变化，再加上北极涛动（AO）或北大西洋涛动（NAO）的负趋势增加，可能是观测到的夏季降水演变模式的原因。
Due to the lack of reliable climatic proxies, the variability of precipitation in “Westerlies-dominated” arid central Asia (ACA) during the Holocene is debated. Here, we present a high-resolution (ca. 100 years per sample) organic carbon isotopic composition (δ13Corg) record from bulk samples from the Lujiaowan10 section in the northern piedmont of the Tienshan Mountains, Xinjiang Province, northwestern China. A robust chronology is provided by K-feldspar pIRIR dating. During the early to middle Holocene, from 12 ka to 6 ka (1 ka = 1000 years ago), the δ13Corgvalues are relatively invariant with an average of around −22.5‰. After about 6 ka, the δ13Corgvalues exhibit an overall negative trend with the most negative value of −25.2‰ occurring in the uppermost part of the section, within the interval of Holocene soil formation. Our investigation of the relationship between modern climatic variables and surface soil δ13Corgvalues from the region reveals a significant negative correlation between surface soil δ13Corgand summer precipitation amount (June to August). Therefore, we used the calibration model between summer precipitation amount and surface soil δ13Corgto quantitatively reconstruct the Holocene summer precipitation history of the study area. Our results indicate that summer precipitation in the region was the lowest (ca. 85 mm) during the early to middle Holocene (12–6 ka); however, after 6 ka, the precipitation increased continuously to about 137 mm per year at the present. Our reconstruction is generally consistent with climate simulation results and with regional effective moisture records. Thus, we conclude that the highest summer precipitation, and therefore the wettest climate, occurred in the late Holocene. Decreasing Northern Hemisphere summer insolation may have effected a change in the CGT (circumglobal teleconnection) from a positive to negative phase and, together with more negative trends in AO (Arctic Oscillation) or NAO (North Atlantic Oscillation), may have been responsible for the observed pattern of summer precipitation evolution.