青海湖流域土壤年代学及其气候背景分析

Soils on the Tibetan Plateau are the key to the ecological security. According to the similarity between history and future, it is very important to gain the age of different soils and revealing the relationship between soil and climatic change during geological history, which will give us an important enlightenment for the soil resources suitability under the global warming of today. Qinghai Lake is a hot spot on Quaternary researches, and abundant paleoclimatic recods have been excavated. Therefore, it provides us an opportunity to analyze how different soils in Qinghai Lake basin form and develop under the different climatic background. In this project, genetic horizons classified by using the theory of pedogenesis from about 25 soil sections including alpine meadow soil, mountain meadow soil, alpine steppe soil, frigid desert soil and bog soil will be dated by OSL and radiocarbon dating. These dating results will be summarized by probability density function to determine the age of different type soils. Soil samples are analyzed to obtain the element geochemistry characteristics, total orgnic carbon and total nitrogen content, and the chemical index of alteration (CIA), Rb /Sr ratios and ba value are calculated to evalute the chemical weathering intensity of soil. Combined with the previous climatic records in Qinghai Lake, the background of soil formation, development and succession are analyzed, then the law of different soil successions and the soil responding pattern to climatic change in Qinghai Lake basin will be revealed. The mountain environmental changes with elevations since 14 ka will be reconstructed by phytolith records and soil organic carbon isotope variations as an important complement for the whole Qinghai lake environmental change.

青藏高原土壤是维系生态安全的关键。利用地质历史相似性原理，获取土壤形成的年代及其对当时气候环境的响应机制，对全球变暖背景下，土壤资源可持续发展具有重要参考价值。鉴于青海湖是第四纪研究热点，产出了丰富的古气候记录，为该流域土壤形成、发育提供了可靠而完整的古气候背景。本项目拟在青海湖流域选取山地草甸土、高山草甸土、高山草原土、高山寒漠土与沼泽土代表性剖面25个左右，从土壤发生学角度出发，进行土壤地层划分，采用OSL测年方法获取各土壤发生层年代，利用概率密度函数获取各类土壤的形成年代。利用元素地球化学、有机质含量等，计算CIA, Rb/Sr, ba等土壤风化指数，评价成壤强度。结合青海湖气候记录，分析各类土壤形成、发育、演替的气候背景，揭示该区土壤演替规律及其对气候的响应。利用土壤中有机碳同位素、植硅体、地化元素特征等指标重建和对比青海湖末次冰消期以来山地环境演变的海拔异同性，进一步补充和完善青海湖流域环境演变过程。

项目的背景 青藏高原土壤是维系生态安全的关键。利用地质历史相似性原理，获取土壤形成发育的年代及其对当时气候环境的响应机制，对全球变暖背景下的土壤资源可持续发展具有重要参考价值，为预测未来土壤演替趋势提供重要参考。鉴于青海湖流域是第四纪研究热点区域，已有的丰富古气候古环境记录为本项目提供了研究基础。主要研究内容 在青海湖流域已选取高山草甸土、山地草原土与沼泽草甸土代表性剖面40个左右，基于土壤发生学进行各剖面的土壤发生层划分，采用OSL测年方法获取各土壤发生层（草毡层、母质层为主）年代，利用概率密度函数获取各类土壤的形成发育时间，计算成土速率。利用粒度、元素地球化学、TOC、TN等土壤理化性质指标，评价成壤强度和估算土壤营养元素累积速率。结合青海湖古气候古环境记录，分析各类土壤形成、发育、演替的气候背景，揭示该区土壤演替规律及其对气候的响应。重要结果与关键数据 ①光释光测年方法对高原土壤测年是适用和可靠的。②经高密度OSL测年发现：高原土壤剖面存在着广泛的沉积间断；末次冰消期和早全新世（>8 ka）风沙活动强烈，风尘沉积速率较高；中全新世（~7-5 ka）风尘沉积速率较低；晚全新世（~4 ka）以来风尘沉积速率最高。③青海湖流域各类土壤母质多以风尘为主，土壤发育以风尘加积和风尘混合加积模式呈现。④利用土壤中孢粉含量指标重建青海湖早全新世（~8.5 ka）以来高海拔（>3500 m）地区生态景观格局演替过程。科学意义 ①基于动态的第四纪地质年代学和静态的土壤发生学，通过OSL测年方法测得高原土壤形成发育于间冰期和间冰段，将为全球变化、高寒地区生物地球化学循环、高寒生态系统演替等研究提供理论基础。②风尘对高原土壤的形成具有重要贡献，在千年时间尺度上以风尘加积型发育模式为主。③结合土壤中孢粉含量变化，获取了全新世不同气候变化背景下植被、土壤的演替规律，在中全新世7-4 ka，青海湖海拔3500米的山地土壤为草甸土，随后演替为草原土，距今0.6 ka演化为草甸土，该研究对预测未来气候变暖背景下土壤演替趋势提供了重要参考。