乌伦古湖全新世气候变化的环境磁学记录

HOLOCENE ENVIRONMENTAL CHANGE REORDED BY MAGNETIC PROPERTIES OF WULUNGU LAKE SEDIMENT

对位于新疆北部阿勒泰地区福海县的乌伦古湖WLG10C孔岩芯进行了环境磁学分析,以平行孔(WLG10B)AMS^(14)C测年为年代框架,重建了该地区全新世以来气候环境变化。结果显示:1)乌伦古湖磁性矿物以细颗粒亚铁磁性矿物为主,并含有少量不完整反铁磁性矿物和富铁绿泥石类粘土顺磁性矿物,磁学参数x_(ARM)和x_(ARM)/x可用作气候变化代用指标,记录了研究区气候环境变化;2)研究区在全新世早期(7300eal.aB.P.以前)为冷干气候,中、晚全新世(7300cal.aB.P.以来)为暖湿气候。在4600cal.aB.P.左右为该湖高湖面时期,在3500～2500cal.aB.P.之间存在与全球范围一致的突发冷事件。乌伦古湖全新世气候变化与周边环境记录较一致,气候变化模式符合中亚干旱区全新世气候变化西风模式。

There has been long lasting debate on the climate change mode during the Holocene in Xinjiang region where the climate is very sensitive to the terminal lakes in arid areas. The Wulungu Lake, located in Fuhai county, Xinjiang, Northwestern China, traverses the area between 46°59＇ - 47°25＇N and 87°00＇ - 87°35＇E, with an area of 927km2 and a maximum depth of 16m（ average depth is 8m）. Two parallel eores,WLG10B with a length of 397cm and WLG10C with a length of 271em, were obtained in the northeast corner of the lake area （47°21＇50.5＂N, 87°27＇07.2＂E）. Environmental magnetic parameters of the lacustrine sediments of WLG10C core were conducted. Low frequency （470Hz）and high frequency （4700Hz）magnetic susceptibilities were measured by a MS2 magnetometer （Bartington, England）, ZARM was calculated based on the ARM measured by a DTECH AF demagnetizer with a peak AF field of 50mT and DC bias field of 0.05mT. IRMs and SIRM were imparted by an MMPM10 pulse magnetizer, while all remanence measurements were made by a Minispin magnetometer. Thermomagnetic curves（J-T curve）were determined using a variable field translation balance （VFTB） （heating/ cooling cycles were measured from 25℃ to 700℃ in ll4mT magnetic field）. WLG10C core date framework was established based on AMS14C age dating,from which the age of the core at the depth of 230cm was determined as about 7300aB. P. The climate change during the Holocene of Wulungu Lake was reconstructed. The result shows that the main magnetic minerals in the sediments are fine-grained ferrimagnetic minerals,with a small amount of anti-ferromagnetic and paramagnetic minerals. As a potential climate proxy, XARM and XARM/X of the lake sediment can be used to reconstruct palaeoenvironment in the arid area. The magnetic proxies implied that the environment during the Early Holoeene was cold and dry,while that during the Middle and Late Holocene was warm and wet. The lake surface level is high during about 4600cal. aB. P. There was a sudden cold event between 3500cal. aB. P. and 2500cal. aB. P., which is consistent with the global cold event during the same period. The climate change during the Holocene recorded by WLG10C is consistent with the records in its adjacent areas,and obeys ＂the arid Central Asian westerly mode＂.