天山科其喀尔冰川区水化学侵蚀过程研究

From 1906 to 2005, the global mean surface air temperature increased by 0.74±0.18 ?C, increasing, especially since approximately 1950. With the extensive alpine glaciation in western China, the mean surface air temperature increase of 0.6?C (i.e., 0.2?C per decade) in the Tarim basin has resulted in the alpine air temperature also exhibiting a remarkable rising trend which has influenced the alpine hydrology in western China. Eighty-two percent (82.2%) of glaciers in China have retreated, and the glacial area has reduced by 4.5%. Since warming-induced alpine glacier melting is likely to intensify, water-rock interactions such as sulfide oxidation and carbonate dissolution are also expected to increase. Glaciation is responsible for significant drawdown of atmospheric CO2, generating a negative feedback on climate. It has long been recognized that rates of terrestrial chemical erosion may influence the atmospheric concentration of CO2, a radiatively important gas contributing to mean global temperature regulation. Because of its potential impact on climate at glacial-interglacial timescales, CO2 sequestration during episodes of deglaciation has attracted considerable attention. In glacierised region, the studies of hydro chemical erosion mechanisms and erosion rate can offer valuable references for the researches of water-quality assessment and riverbed evolution in arid and semi-arid area. The Koxkar glacier, located in western Mt.Tienshan, China, is the largest glacierised area of monitoring glaciers with debris. The project will study hydrochemical erosion process and determine control factors in glacierised region. Evolutions and changes of soluble ionic of natural different water are main lines of research.Combined with the data of chemical composition of dust, moraine and regional mineral soluble chemical ions on the supraglacier surface, according to the principle of material balance, we shall study the supply sources, proportion and erosion rates in atop bare ice and supraglacial moraine area. Utilizing just the results, aerosol chemical component and monitoring data of H2O/CO2 flux of eddy covariance observation systems, to analyze the process and influencing factors of chemical exchange on vapour/liquid（solid）interface. With tracer tests and chemical analysis results of water from geometrical hydro-channel, to clarify the process of water-rock reaction in englacial channels, and draw a comparison with process of hydrochemical erosion on the glacier surface to study their commonness and otherness. We shall analyze that there are driving force and control factors in glacierised region to assess chemical erosion rate effects on water quality at the river flowing out in different glacier coverage in the same basin using the method of mathematical statistics.

冰川作用区水化学侵蚀不仅是地球表面侵蚀过程研究的重要组成部分之一，也是大气物质组分变化及气-液（固）界面物质交换研究的关键环节之一。区域性而言，冰川区侵蚀机制与侵蚀率研究可以为干旱区出山径流水质评估、河床演变研究提供参考。项目以天山南坡科其喀尔冰川为研究对象，对冰川区侵蚀过程及控制因素进行研究。以各种水体中可溶性物质组分变化和演变过程为研究主线，结合冰面污化物、表碛物及区域矿物质中可溶性物质化学组分，利用物质平衡方法，研究区域水化学侵蚀物质的主要补给来源、补给比例和侵蚀率；融合研究区气溶胶组分及冰面H2O/CO2通量监测结果，分析气-液界面物质交换过程及影响因素；借助示踪试验，揭示冰下/冰内水-岩相互作用过程与冰面侵蚀的共性与差异性。综合冰川物质平衡及相关气象要素观测，以数理统计为手段，探讨冰川区水化学侵蚀的驱动因子及控制因素，评估同一冰川、不同覆盖率下，水化学侵蚀演变对径流水质的影响。

冰川作用区水化学侵蚀不仅是地球表面侵蚀过程研究的重要组成部分之一，也是大气物质组分变化及气—液界面物质交换研究的关键环节之一。区域性而言，冰川区侵蚀机制与侵蚀率研究可以为干旱区出山径流水质评估、河床演变研究提供参考。项目以天山科其喀尔冰川为研究对象，对冰川区侵蚀过程及控制因素进行研究，主要结果有：（1）科其喀尔冰川作用区夏季（6月27日-9月30日）径流深为671.70mm，水化学侵蚀产生的地壳源溶质通量为213.65 ± 10.05 kg⋅(km2⋅d)-1，占流域河水中总溶质通量的53.59%。来源于冰川冰和洗刷气溶胶的降水中可溶性溶质分别为70.02 ± 4.68和16.57 ± 1.13 kg⋅(km2⋅d)-1,仅占径流溶质总通量的17.57% 和4.16%。（2）区域硫化物氧化或大气CO2溶于水产生的H+，可以促使碳酸盐和K/Na/Ca—长石矿物的碳酸化与水解作用。在自然界中，通过硫化氧化产生的H +对于碳酸化与水解反应来说是不足的，但是溶解在水中的大气CO2产生H+可以延续碳酸化与水解反应，因此，在冰川区水化学侵蚀过程可以促使大气CO2在气—液界面发生沉降，对应地6月27日-9月30日的大气CO2暂时性沉降量为804.83 t C，其后续产生的HCO3-占流出总量的39.61%和总流出可溶性离子的24.68%。表明冰川变化可以影响区域大气CO2，尤其是长时间尺度的全球碳循环。（3）在2015-7-21～2017-7-18，利用涡度观测系统（EC）对科其喀尔冰川裸冰区和表碛物分布区进行连续CO2通量监测，前者因冰川消融剧烈引起仪器倾斜，误差较大，但后者结果分析表明：a、大气CO2通量介于-408.95至81.58 mmol（m2 d）-1（平均值 -58.68 mmol（m2 d）-1），表明研究区域是一个重要的碳汇；b、CO2通量足迹贡献区域主要位于EC站150米范围内，其积雪、融雪和冰川融化期间CO2通量分别占总通量的93.30％，91.39％和90.17％。 因此，在EC站观察到的影响CO2通量的贡献区相对集中，表明冰川周围的草地CO2通量对EC站点几乎没有影响；c、雪层中可溶性离子的淋溶作用及化学反应也可能促进大气中的CO2沉降。同时，积雪和几乎封闭的冰内水文通道限制了径流的形成，但可为水化学侵蚀提供足够的反应时间，促进冷季CO2没收。