青藏高原及邻区湖泊沉积物OSL和14C测年对比研究：评价晚第四纪高湖面的年代框架及碳库效应的时空变化

The prior project (grant 40901014) focused on the timings of the evolution of Huahai Lake during the late Quaternary. Six papers supported by this project have been published in international SCI journals. As first-author or corresponding-author, the applicant led five of these publications. The main results suggested that (1) inconsistent chronology of lake highstands in different lakes was possibly caused by the difference in dating techniques (e.g. 14C dating or OSL dating), and (2) the reservoir effects of 14C ages varied spatially and temporally in different lakes and sometimes even in the same lake. As OSL results are assessed and thus considered to be reliable, the inconsistence between OSL and 14C chronologies for the same sediment sequence (older than 30 ka BP) could be attributed to the underestimation of radiocarbon dating. In order to further seek the phenomenon of disagreement results of 14C dating or OSL dating for the relatively old strata (>30 ka BP) and its mechanisms, we propose to select two sets of strata from Zhuye Lake and Qarhan Lake respectively as our study materials for comparison of two kinds of dating techniques. Some preliminary researches have already been done in these three lakes, which are useful for the proposed project. Besides, two cores from Nam Co and Tangra Yum Co have also been obtained already. Based upon these two cores, spatial and temporal variations in radiocarbon reservoir effects of lake sediments are proposed to evaluated and calibrated by the comparison with high resolution OSL dating.

青年科学基金项目开展了河西走廊花海及邻区晚第四纪湖泊演化的年代学研究。结果表明，14C和OSL等测年技术不同可能是导致认识晚更新世高湖面年代学差异的主要原因；湖泊沉积物14C年龄碳库效应存在时空差异。该项目资助在Quaternary Research，Quaternary International，Quaternary Geochronology以及The Holocene等国际SCI刊物上发表6篇论文（其中5篇的第一作者或通讯作者是项目申请人）。针对青年科学基金项目的研究结果以及其它湖区的前期工作，申请项目拟选择两个湖泊（即猪野泽和察尔汗）开展较老地层（>30 kaBP）的14C和OSL测年技术的对比研究，以期进一步揭示青藏高原及邻区晚更新世高湖面年代学存在差异的原因；另外，拟以纳木错和当惹雍错的沉积物岩芯进行利用OSL测年技术校正湖泊钻孔沉积物14C年龄碳库效应时空变化的可行性研究。

该面上项目（41271002，2013-2016）是青年科学基金（40901014，2010-2012）的后续资助。前期的青年科学基金项目开展了河西走廊花海及邻区晚第四纪湖泊演化的年代学研究，初步认为，14C和光释光（OSL）两种测年技术对青藏高原及周边晚更新世高湖面形成时间的测年结果差异较大。面上项目选择“MIS3a大湖期”的猪野泽古湖，对该区域的高水位湖相阶地开展了系统的OSL和14C测年对比研究，所得14C年代均在40-30 ka范围内，与以往的结果基本吻合，然而同一地层的释光年代则约为100-70 ka，表明该高湖面形成于MIS5阶段。经过释光年代的大量检验并证实其可靠性后，提出晚更新世高湖面事件的14C和OSL年代的差异源自14C测年对样品真实年龄的低估。通过东北兴凯湖湖心的一个相对连续的晚第四纪沉积序列的49个OSL和14个14C测年数据对比研究，为进一步探明晚更新世（>30ka）湖相沉积地层两种测年结果差异及14C测年低估提供了新的证据。此外，项目关于青藏高原东北缘秦王川盆地和东北兴凯湖地区的风成沉积记录也佐证了MIS 3a阶段可能不存在气候湿润和高湖面事件。秦王川盆地内的古沙丘OSL测年结果表明，在约40-13 ka期间风成沙堆积盛行，指示当时的区域气候环境干冷而非暖湿。东北地区的兴凯湖，也在MIS3阶段后期和MIS2阶段发育了由风成砂堆积形成的湖岗，指示当时湖泊退缩，季风降水下降，与区域甚至全球的干冷气候相对应。综合以上年代学和地质记录两方面，对传统的MIS3a大湖期和湿润期的假设提出了质疑，也为晚更新世高湖面事件发生时间提供了新年代学证据。项目还通过多个湖泊沉积序列的两种测年数据的直接对比，发现腾格里猪野泽古湖的“碳库效应”对14C测年影响较小，然而青藏高原南部两个湖泊（当惹雍错湖和纳木错）的研究则体现了湖泊沉积物14C年龄碳库效应随时间和空间发生变化的复杂性。该项目资助在Scientific Reports，Earth and Planetary Science Letters，Quaternary Geochronology，Boreas，The Holocene，Quaternary International等SCI刊物上发表11篇论文（其中9篇的第一作者或通讯作者是项目主持人），在《第四纪研究》，《湖泊科学》等核心刊物上发表4篇论文。