新疆阿尔泰全新世双湖沉积物正构烷烃分布及其环境意义

文章对新疆阿尔泰双湖沉积物进行了古气候、古环境变化研究。双湖（48°52'N，87°02'E）位于阿尔泰山中部，是山谷岩石滑塌阻塞形成的堰塞湖，湖长约1200m，宽度约300m，最大水深9m。项目使用重力钻在双湖中心钻取了172cm无扰动岩芯，根据核素测年（¹³⁷Cs，²¹⁰Pb，AMS¹⁴C）建立了9.1cal. ka B.P.以来的时间标尺，以正构烷烃分布特征（ACL_23~33、nC₂₇/nC₃₁、P_aq）为指标，重建了该区的古植被、古气候变化。沉积物中正构烷烃以高碳数为主，中长链正构烷烃存在显著的奇碳优势。链长指标（ACL_23~33）、nC₂₇/nC₃₁指标、P_aq之间具有很强的相关性关系，表明指标可能受到相似的气候驱动因素影响，反映了区域植被和湖泊水生生物的演替历史：9.1~8.8cal. ka B.P.期间水生植被输入较少，陆生植被中草本植物相对占比较高；8.8~3.3cal. ka B.P.期间大型水生植物大量繁殖，汇水区木本植物增多；3.3cal. ka B.P.至今湖泊周围的木本植物减少，草本植物相对占比增多，水生植物输入减少。双湖沉积物ACL_23~33指标自9.1cal. ka B.P.以来呈逐渐增加的趋势，可能表明温度逐渐增加，这一结果与前人在该区利用泥炭br-GDGT重建的温度序列具有相似的变化趋势，但在百-千年尺度上，温度变化不一致，可能与指标的敏感性和定年精度有关。

n-Alkane distribution and their paleoenvironmental implications during Holocene in lacustrine sediments in Lake Shuang,Xinjiang

The Altai Mountains are located at the junction of Asia and Europe. It is far away from oceans, and typical temperate continental climate. Moisture sources are mainly from the Atlantic and Arctic Oceans, as well as from recycled moisture from the Mediterranean Sea, the Caspian Sea and the Black Sea in the middle latitude. It is one of the key regions to study paleoclimate change. Here, we present a paleoclimatic and paleoenvironmental record from the sediments of Lake Shuang. Lake Shuang(48°52'N, 87° 02'E) is located in the middle of the Altai Mountains and was formed by the landslide damming of a valley. The lake is about 1200m in length, 300m in width, and a maximum depth of 9m. Sediment cores were collected by using a gravity corer and obtained a 172cm sediment profile without disturbance. The chronology of sediment cores during the past 9.1cal. ka B.P. is based on radiometric dating data such as 137Cs, 210Pb and AMS14C. The n-alkane proxies such as average chain length(ACL23~33), grass/tree ratio(nC27/nC31) and Paq ratio(Aquatic Plant n-alkane Proxy) were used to reconstruct vegetation and climate changes over the past 9.1cal. ka B.P. The result indicates that the sediments are dominated by middle-and long-chain n-alkanes in the range of nC23~nC33 with a strong odd over even carbon number predominance. There is a strong correlation among ACL23~33, nC27/nC31 and Paq, which may suggest that these proxies may be affected by the similar climate driving factors and reflect the succession history of vegetation. The n-alkane proxies suggests less input of aquatic vegetation in the sediment in the interval of 9.1~8.8cal. ka B.P., followed by an increase of herbaceous and aquatic plants between 8.8cal. ka B.P. and 3.3cal. ka B.P., while a decrease of woody plants and increase of herbaceous plants after ca. 3.3cal. ka B.P. The ACL23~33 values show an increasing trend over the past 9.1cal. ka B.P. that suggest a warming trend since the Early Holocene. Although it is similar with previous br-GDGT-based temperature reconstruction from our study region, it is not well correlated at centennial-millennial time scale probably due to uncertainties in proxy sensitivity and chronology.