青藏高原典型大陆性冰川表面消融期溶解性有机质演化特征分析——以祁连山老虎沟12号冰川为例

冰尘是冰川消融区表面黑色或棕色的球状聚合体，是冰川表面微生物的主要聚集区，同时含有丰富的溶解性有机质（dissolved organic matter， DOM），在冰川物质能量平衡、生物地球化学循环特别是碳循环中发挥着重要作用。在冰川消融期，受环境条件和微生物活动水平等方面的影响，冰川表面DOM的含量是动态变化的。为了研究冰尘中DOM的演化过程，于2017年7月在青藏高原东北部典型大陆性冰川老虎沟12号冰川消融区表面开展了为期18天的冰尘原位培养实验。结果显示：培养初期（第0~6天），冰尘水样中溶解性有机碳（DOC）浓度从13.41 mg?L^-1显著降低到4.47 mg?L^-1，培养后期（第6~18天），增加至6.71 mg?L^-1；用特征紫外吸光度SUVA₂₅₄分析培养期间“光-生物”演化过程对DOC吸光性的影响，结果表明：SUVA₂₅₄的值先显著降低后显著升高，表明长时间的光照和微生物作用导致DOC浓度增加的同时，具有光吸收作用的化合物含量也显著增加。利用傅立叶离子回旋共振质谱分析DOM的分子组分发现，整个培养过程中（第0~18天），DOM中多肽类和脂类分子含量明显减少，不饱和烃类、芳烃类以及多环芳烃类化合物含量增加。分析第0天，第6天，第9天和第18天四个培养时段特有DOM分子组成的变化发现，“光-生物”演化过程使得冰尘中DOM的组成不断由脂类和多肽类向不饱和烃类、芳烃类以及多环芳烃类化合物转化。

The evolution characteristics of dissolved organic matter in cryoconite during ablation season on the surface of a typical continental glacier of Tibetan Plateau:a case study at Laohugou Glacier No.12

Cryoconite is black or brown spherical aggregates on the surface of glacier ablation areas， which is an important sink for microbe and dissolved organic matter （DOM） accumulated in supraglacial environments. Therefore， cryoconite plays an important role in glacier mass and energy balance， and biogeochemical cycle （especially the carbon cycle）. During the ablation season， the concentration and characteristics of supraglacial DOM changes dynamically which are influenced by the environmental conditions and microbial activity. This study characterized the evolution of DOM from cryoconite throughout a 18-day in situ incubation experiment in the ablation zone of Laohugou Glacier No.12 and applying comprehensive analyze method as follows： dissolved organic carbon （DOC） analysis， UV-visible spectroscopy （UV-vis） analysis and electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry （ESI FT-ICR MS） analysis. The results show that the concentration of DOC in cryoconite water decreased significantly from 13.41 mg?L^-1 to 4.47 mg?L^-1 during the early incubation （from day 0 to day 6）， but then gradually increased to 6.71 mg C?L^-1 during the late incubation （from day 6 to day 18）. The value of SUVA₂₅₄， which was used to analyze the effect of the coupled ‘photo-biological’ influence on the light absorption of DOC during the incubation period， was also decreased firstly and then increased significantly， indicating both of the concentration of DOM and the content of light absorbing compounds increased during the long-term incubation due to the light and microbial affect. The changes of DOM composition analyzed through ESI FT-ICR MS suggested that during the whole incubation period （from day 0 to day 18） the contents of peptides and lipids were reduced， while the contents of unsaturated， aromatics and condensed aromatics were increased. The changes of unique DOM composition in day 0， day 6， day 9 and day18 revealed that the composition of DOM in cryoconite continuously transformed from aliphatics and peptides to unsaturated， aromatics and condensed aromatics by the coupled ‘photo-biological’ transformation.