利用高海拔雪冰中的微粒研究亚洲粉尘中铁元素的含量和溶解度

The iron contained in the long-range transported Asian dust (mineral aerosol) can deposited in the high-nutrient low-chlorophyll Pacific Ocean and act as the limiting nutrient to stimulate the growth of oceanic phytoplankton, which can uptake atmospheric CO2 and therefore partly counteract the global warming caused by anthropogenic greenhouse gas emission. Iron content and solublity are the two key paramerter to accurately assess Asian dust's contribution to iron nutrient supply and consequently its contribution to the CO2 fixtation. Snow and glaciers from high-alpine mountaines in western China are excellent media to preserve the Asian dust. Dust particles in snow and ice cores from High Asia are the analogue of the one that can be long-range transported in the mid- and upper troposphere by Westerlies to the Pacific and server as nutrient supply. Based on the "Iron Hypothesis", this project is planned to carry out researches as following: to analyze the iron content and solubility of Asian dust in snow and ice cores from Qilian Shan, Himalayas, Pamirs, Tien Shan, etc., in order to reveal their spatial difference in total and dissolved iron contents of Asian dust that derieved from different emission regions; to study the factors (e.g. mineral, pH value, grain size, etc.) that can impact the iron solubility in Asian dust, and distinguish their level of impact on iron solubility; to set up the quantitative transfer function between the acidity (pH value) and iron solubility through control experiments, which simulates the possible variation that the Asian dust might encounter during the transport to Pacific Ocean. This project will provide fundamental data for the reliable and quantitative assessment on the iron supply to oceanic bioactivity and consequently the CO2 stabilization by Asina dust, and furtherly contribute to our understanding on the physical and chemical characteristics of Asian dust.

亚洲粉尘对太平洋高营养低叶绿素海区的铁养分供给可以促进浮游生物的生长和大气中CO2的固定过程，从而可以减缓温室气体导致的全球变暖。确定粉尘中铁元素的总量和溶解度这两个关键的参数，是准确估算亚洲粉尘的铁养分供给能力及相应的固碳贡献的基础。中国西部高海拔的雪冰是亚洲粉尘的独特载体，其中的粉尘颗粒代表了可以被远距离传输到太平洋的那部分亚洲粉尘。以"铁假说"为背景，本项目通过分析典型地点（祁连山、喜马拉雅山、帕米尔、天山等地）雪冰和气溶胶样品中的铁元素，揭示亚洲粉尘在其初始搬运阶段的总铁和可溶铁的含量；通过分析粉尘的粒度和矿物等，探讨这些因素对铁的溶解度的影响；通过开展条件控制实验，建立雪冰粉尘中铁的溶解度与酸度的函数关系。本项目将深入研究亚洲粉尘的物理化学性质，为定量化估算亚洲粉尘对海洋生物铁养分的供给及对大气中CO2固定的贡献提供关键的参数，并为深入认识粉尘的气候效应提供基础。

大气粉尘是重要的气候环境因子，它通过影响大气太阳辐射、生物地球化学循环和雪冰反照率，从而影响到全球气候。粉尘的基本特征是定量评估粉尘气候环境效应的关键。粉尘中的铁元素是影响其辐射效应和养分效应的关键因子。本项目通过研究中国西部高海拔雪冰载体中粉尘的单颗粒形貌与矿物组成、铁氧化物的漫反射光谱、铁元素的丰度和溶解度，提供了准确估算亚洲粉尘的铁养分供给能力的基础数据。研究地点和对象包括天山乌鲁木齐1号冰川表雪、祁连山七一冰川表雪、敦德浅冰芯、慕士塔格冰芯、藏色岗日冰芯、木嘎岗穹冰芯、羌塘1号冰芯、普若岗日冰芯、枪勇冰芯、作求普冰芯以及青藏高原和周边地区的表土，研究指标为粉尘单颗粒矿物与形貌、赤铁矿和针铁矿反射光谱强度和粉尘的元素组成，并对典型样品进行了酸化试验，以检验酸度对铁溶解度的影响。.研究确定了青藏高原多个地点冰芯粉尘元素分析，获得了粉尘铁元素的丰度和溶解度的关键数据。不同地点冰芯粉尘的铁丰度相差不明显，平均值为3.1%~4.8%，但铁元素的溶解度变化极为显著（0.01%~7.95%）；在同一地点，铁溶解度的波动范围都超过了一个量级以上，部分地点甚至达到了2个量级。粉尘漫反射光谱曲线的一阶导数值在430nm和560nm处出现峰值，分别对应针铁矿和赤铁矿，其峰值强度与含铁量相关，并随含铁量的增加而迅速升高；当铁的含量超过一定的阈值后（29 ug cm-2），一阶导数值趋于平稳。敦德冰芯、慕士塔格冰芯和帕隆4号冰芯中的粉尘颗粒主要由石英（17~36%，数量比值，下同）、粘土矿物（37~48%）和长石（12%~18%）组成，伊利石和绿泥石是主要的粘土矿物，高岭石含量极少。粘土矿物的相对比例在敦德冰芯中最高，而石英在帕隆4号冰芯中相对含量最高。在形貌上，冰芯中粉尘颗粒的纵横比和圆度分别为1.48和1.53；在不同地区、不同矿物种类的粉尘颗粒，其纵横比和圆度存在差异。.上述研究结果为理解亚洲粉尘的气候环境效应（尤其是估算固定CO2的铁养分供给）提供了关键的基础数据。