天山南坡科其喀尔冰川流域水化学侵蚀及大气CO_2沉降量分析

Chemical Denudation Rates and Carbon Dioxide Sink in Koxkar Glacierised Region at the South Slope of Mt. Tianshan,China

2004-06-21～2004-09-10对天山南坡科其喀尔冰川作用区河水、大气降水及冰川进行水化学采样和分析实验,计算了地壳源物质的化学侵蚀率和大气CO2沉降量.分析结果表明,大气降水中溶质补给率平均为60.7kg.(km2.d)-1,占流域总溶质通量791.2kg.(km2.d)-1的7.7%.冰川冰中溶质因冰溶解作用补给河水中溶质的补给率平均为60.2kg.(km2.d)-1,占7.6%.地壳源水化学侵蚀率为558.0kg.(km2.d)-1,占70.5%,是河水中可溶性离子的主要来源.其中,流出SO24-总通量为171.1kg.(km2.d)-1,主要来源于地壳水化学侵蚀补给,占90.6%,其次是大气降水补给,占5.6%;流出HCO3-总通量为308.9kg.(km2.d)-1,其中硫化物氧化作用导致碳酸盐水解补给的HCO3-为84.2kg.(km2.d)-1,在吸收大气CO2引起的碳酸化作用过程中,源于大气CO2的HCO3-与源于碳酸盐的HCO3-相等,均为112.3kg.(km2.d)-1,相当于暂时性吸收大气CO2通量为81.0kg.(km2.d)-1,占流域总溶质通量的14.2%.利用碳酸盐水解法计算的地壳溶质侵蚀通量为641.1kg.(km2.d)-1,比前者利用物质平衡原理计算过程中考虑与不考虑大气CO2沉降的结果分别相差14.9%和4.4%.本研究对于评估我国西部资料匮乏的冰川区的水化学侵蚀和冰川区对碳循环的贡献具有重要的示范意义.

Chemical denudation rates and carbon dioxide sink were from water samples from ice-melt water,precipitation and river water were collected daily from June 21st to September 10th in 2004 in the Koxkar glacier region,south slope of Mt. Tianshan,China. The law of conservation of mass was applied for calculating chemical denudation fluxes and transient carbon dioxide sink. It is found that：① There were average of 60. 7 kg·（km^2·d）^-1 and 60. 2 kg·（km^2·d）^-1 solutes supplied by precipitation and ice melt-water respectively which accounted for about 7. 7% and 7. 6% of the total solutes of bulk river water [791. 2 kg·（km^2·d）^-1 ]. Consequently,the rate of chemical denudation derived from the crustal flux was 558. 0 kg·（km^2·d）^-1 ,accounting for 70. 5%. ② Carbonation weathering was 308. 9 kg·（km^2·d）^-1 ,and heavier than that of the other chemical denudations. The crustal concentration of bicarbonates （ HCO 3-） is attributed chiefly to the carbonation of carbonates （ limestone and dolomite ） and aluminosilicates /silicates. A further important source of bicarbonates and sulphates is pyrite oxidation coupled with limestone /dolomite dissolution. The transient carbon dioxide sink can be estimated by ion balance law,which is 81. 0 kg·（km^2·d）^-1 ,accounting for 14. 2%. ③The chemical denudation rates was 641. 1 kg·（km^2·d）^-1 with relationship of specific conductivity to concentrations of dissolved carbonate in water,which is only 4. 4% less than that obtained from mass balance method without regard to carbon dioxide sink. The study also implied important to evaluate chemical denudation fluxes of poor data in western mountain area,China. However,because of without chemical analysis and ion partitioning,the transient CO2 drawdown cannot be established.