冰尘结构特征及形成分析——以乌鲁木齐河源1号冰川为例

Characteristics and Formation Analysis of Cryoconite Granules:Take the rümqi Glacier No.1 as an Example

利用2007-2010年夏季在乌鲁木齐河源1号冰川采集的5个冰样, 对冰样中冰尘的特征、冰尘中蓝藻的种类及冰尘中无机矿物颗粒的粒度特征进行了分析研究. 研究表明： 冰尘为棕色球状聚合体, 粒径为0.27~3.5 mm, 分布在冰川消融区表面, 其组成成分为有机质、无机矿物颗粒和微生物. 冰尘有4种主要的内部结构： 类型Ⅰ, 具有同心层结构的冰尘;类型Ⅱ, 带有亚颗粒的冰尘;类型Ⅲ, 内部无明显结构的冰尘;类型Ⅳ, 中心位置处具有较大无机颗粒的冰尘. 冰尘中无机矿物颗粒的数量主要分布在d〈3.5 μm的范围内, 且体积分布的粒径众数介于3~25 μm之间. 同时, 对冰尘中的蓝藻进行了16S rRNA基因序列的系统发育分析, 共从蓝藻16S rRNA基因文库中筛选了247个阳性克隆, RFLP分型得到10个不同的OTUs. BLAST比对, 系统发育分析将这10个OTUs归为颤藻目（Oscillatoriales）、色球藻目（Chroococcales）、未定种（Unclassified）. 颤藻目为绝对优势类群, 占整个基因克隆文库的91%. 经估算, 冰尘中存在大量的有机物质和微生物, 无机矿物颗粒只占了很小的比例, 表明影响冰川消融区表面反照率的主要因素为冰尘中的有机部分, 包括有机物质和微生物.

5 ice samples were taken from the ürümqi Glacier No.1, Tian Shan, China from July 2007 to June 2010. The samples were analyzed for the structure, formation process of cryoconite granules, cyanobacteria species and characteristics of mineral particles in cryoconite. It is found that granules were distributed over the entire ice surface of the ablation area, and ranged in size from 0.26 to 3.5 mm （mean 1.1 mm）. It mainly consisted of organic matter, mineral particles and microbes. Microscopy of a thin section revealed four inner structures. Type Ⅰ, most granules had concentric layers of dense organic matter, which are probably derived from annual growth of the granules by the activity of cyanobacteria. Type Ⅱ, some granules contained two or more sub granules. Type Ⅲ, there were also granules that had no specific internal structure. Type Ⅳ, some granules had relatively large mineral particles at their center. The 16S rRNA genes were amplified from the total DNA by PCR with bacteria-specific primers and constructed a clone library. Positive clones were randomly selected from the library and identified by restriction fragment length polymorphism（RFLP）. The unique RFLP pattern corresponded sequences were sequenced, BLAST and then constructed phylogenetic tree. In total, 247 positive clones were screened and grouped into 10 Operational Taxonomic Units （OTUs）. 10 OTUs were divided into 3 phyla with Blast analysis and RDP classifer： Oscillatoriales, Chroococcales, Unclassified. Oscillatoriales（91%） was the absolutely dominant group. Mean mass concentration of mineral particles is d〈3.5 μm. Volume size distributions of mineral particles showed single-model structures having volume median diameters from 3 to 25 μm. There have abundant organic matter and microbe in cryoconite. Thus, the main factor of lower albedo is organic part, include organic matter and microbes.