天山哈密榆树沟冰川冰尘特征及其成因

Characteristics and formation analysis of cryoconite granules of Yushugou Glacier

利用2011年8月在哈密榆树沟冰川采集的5个冰样,通过石蜡切片技术、16SrRNA系统发育分析及无机颗粒粒度分析方法,结合野外考察,对榆树沟冰川冰尘(cryoconite)的结构特征及形成过程进行了分析研究。结果表明:榆树沟冰川冰尘粒径为0.22～2.9mm,由有机部分(蓝藻、有机质)与无机部分(无机矿物颗粒)结合形成球状聚合体,它的生长具有季节性并且具有生长、裂解交替循环的生命周期;通过核糖体DNA扩增片段限制性内切酶分析(Amplifed Ribosomal DNA Restriction Analysis,ARDRA),将蓝藻16SrRNA基因文库中的214个阳性克隆分为9个不同的操作分类单元(Operational Taxonomic Unites,OTUs)。经过基因测序、BLAST比对及系统发育分析将9个OTUs归为:颤藻目,色球藻目和未定类群,其中颤藻目为冰尘中蓝藻的绝对优势类群;冰尘中无机矿物颗粒(d<3.5μm)在数量上占绝对优势,体积分布的粒径众数值为14μm,较其它冰川而言,粒径众数较大。经估算,冰尘中有机部分所占比例明显大于无机颗粒,故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。

Cryoconite granules are dark-colored spherical aggregates of organic and inorganic material on glacier ice,and are commonly observed on glaciers over the world. Cryoconite granules are the main impurities on glacier,it can reduce the albedo of glacier surface markedly. 5 ice samples were taken from the Yushugou Glacier,Hami Prefecture,Xinjiang,China,in August 2011. By using the methods of paraffins section technology,16SrRNA phylogenetic analysis and mineral particles analysis,this paper studied the structure,formation process of cryoconite and discussed the main factor（organic part or inorganic part in cryoconite） of low albedo on glacier. The results showed as follows：（1） cryoconite granules distributed over the entire ice surface of the ablation area or cryoconite holes,and the size ranged from 0.22 to 2.9 mm （mean 1.0 mm）. The compositions of cryoconite granules are mineral particles,organic matter and microbes （cyanobacteria is the main microbe）. Cryoconite granules have four inner structures：Type 1,there are cryoconite granules that have no specific internal structure—mineral particles and organic matter distributes uniformly in the cryoconite. This type may be the primary form of the cryoconite. Type 2,some granules contain two or more sub granules. This type comes from the combination of small cryoconite granules. Type 3,some cryoconite granules have concentric layers of dense organic matter. Type 4,some granules have relatively large mineral particles in their center. Cryoconites have seasonal growth and an annual cycle of growth and dissociation. （2） 214 positive clones were randomly selected from the clone library and these positive clones were screened and grouped into 9 operational Taxonomic Units （OTUs） through ARDRA. 9 operational Taxonomic Units were divided into 3 phyla through sequences of gene,blast analysis and phylogenetic analysis：Oscillatoriales,Chroococcale and Unclassified. Oscillatoriales（95.8%） was the absolutely dominant group. （3） Mean mass concentration of mineral particles on the Yushugou Glacier was d〈3.5 μm,volume median diameters of volume size distributions of mineral particles was 13 μm. Based on a comparison of the volume median diameters of volume size distributions of mineral particles between Urumqi Glacier No.1 and Qingbingtan Glacier No.72,the volume median diameters of mineral particles on the Yushugou Glacier is higher. （4） the size of cryoconite ranged from 0.22 to 2.9 mm （mean 1.0 mm）,so the mean volume of single cryoconite granule is 4.13 mm3. However,the mean size of single mineral particle is only 3.28 μm and the number of mineral particles in single cryoconite granule is small. After estimation,the proportion of organic matter is higher than that of mineral particles. The conclusion is that there are abundant organic matter and microbes in cryoconite,so the main factor of lower albedo is organic part,including organic matter and microbes. The previous researches mainly focus on the influence of mineral particles and black carbon on albedo of glacier ablation. Cryoconite granules as the crucial impurities on glacier can reduce the albedo of glacier surface markedly. However,the characteristics and formation process of cryoconite were rarely studied in China. It is a new field in the glacier area. Thus it is important to study the cryoconite on glacier.