青海湖现代内生沉积和生物地球化学过程的季节和年际变化—基于时间序列沉积物捕获器的高分辨率研究

Sediment traps have been successfully used to examine the modern processes of settling particle fluxes and compositions in oceans and foreign large lakes, but no relevant work has carried out in inland lakes in China. The relative lack of understanding of the modern processes of settling particle matter in Lake Qinghai has become one of the biggest barriers to further investigation of paleoclimate and paleoenvironment by using sediment cores. In this proposal, four McLane Mark 8-13 time-series sediment traps, with 13 cup sample bottles, will be deployed synchronously for three whole years at southern sub-basinal depositional center in Lake Qinghai to collect seasonal settling particles in situ and measure sample export flux and seasonal variability. By analyzing geochemical compositions of particles, organic matter and adult ostracod shells of these time series settling samples collected by the sediment traps, along with mineralogy and diatoms as well, we try to understand in-depth seasonal variability in modern mass fluxes and compositions in Lake Qinghai. Correlating fluxes and compositions with state-of-the-art sensing data of lake water parameters and meteorological and hydrological data will help to recognize the controlling factors of the modern processes of endogenic precipitation fluxes and compositions. These results are fundamental to palaeoenvironmental interpretations. Following the pilot deployment of the sediment trap in Lake Qinghai, we believe that the data after this work will offer a novel perspective to achieve a comprehensive knowledge of particle and bio-geochemical processes within this important lake and it will provide a great case study on modern sedimentation processes in inland water bodies at various geographical settings in China by using time series sediment trap.

现代过程认识的相对缺乏已成为利用湖泊沉积物反演古气候环境的瓶颈之一。时间序列沉积物捕获器为原位连续采集水体中沉降颗粒物而设计，在认识现代沉积过程方面具独特优势。本项目拟在青海湖南盆沉积中心放置时间序列沉积物捕获器及传感器，获取青海湖三年连续的季节性沉降颗粒物样品和湖水环境参数；通过颗粒物沉降通量、矿物学、硅藻、介形类壳体和有机质的稳定同位素等地球化学组成的分析，查明青海湖内生物质通量与组成的季节性变化特征；加上2010年以来采用同型捕获器所获得的样品和数据，结合实时监测的湖水参数和流域水文气象资料，揭示青海湖现代内生沉积和生物地球化学过程的季节性和年际的时空变化及其控制因素，为沉积岩心古气候环境相关代用指标的机理解释提供科学基础和依据，并为我国内陆湖泊现代过程研究手段和内容的拓宽提供研究范例。

针对青海湖现代沉积过程相对缺乏的现状，本项目计划利用时间序列沉积物捕获器原位连续采集青海湖水体中沉降颗粒物，通过分析其颗粒物沉降通量、矿物学、硅藻、介形类壳体和有机质的稳定同位素、生物标记物等地球化学组成，揭示青海湖现代内生沉积和生物地球化学过程的季节性和年际的时空变化及其控制因素，为沉积岩心古气候环境相关代用指标的机理解释提供科学基础和依据。通过为期四年的项目执行，系统开展了沉积物捕获器在2010-2012年采集到的季节性颗粒物样品的矿物学和元素分析，结合流域基岩和粉尘数据，获取输入青海湖物质来源及内生物质与河流和粉尘等外源输入相对比例、地球化学组成的季节性变化，有效区分青海湖现代内生物质季节性的变化及通量，特别是对于冬季冰封期间湖泊物质（无机、有机）来源和通量；完成了介形类壳体和自生碳酸盐矿物的氧碳同位素分析，获取青海湖介形类壳体氧碳组成及其季节性和年际变化，结合流域水文和气象资料、实时监测的湖水温度、电导率、盐度、氧逸度等数据，探讨了影响青海湖季节性介形类壳体和自生碳酸盐的气候环境因子及其控制因素，评价各参数的环境指示意义。.主要进展包括：（1）获得了青海湖2010-2012年总颗粒物、<63 μm颗粒的沉积通量和碳酸盐含量随着季节的变化；（2）明确了青海湖介形类壳体氧碳同位素季节和年际变化及其控制因素；（3）鉴定了青海湖硅藻种属及其季节性分布；（4）本建立了微量样品的生物标记物和Li、Mg同位素测试分析方法，但由于每次获得的样品极少，未能获得生物标记物和同位素的有效数据。.值得提出的是，经多次努力，三个捕获器未能打捞回来，特别是因疫情的影响，未能继续放置沉积物捕获器。因此我们将研究思路转向一些河流现代过程的示踪研究，包括黄河中游和岷江流域，并已发表了相关的研究成果。这些工作对于理解季风区现代地表地球化学过程的季节和年际变化具有同样的指示和启示意义。