天山南坡科其喀尔冰川作用区CO_2通量观测研究

Observations and study of the CO_2 flux in the debris of the Koxkar glacier,Tianshan Mts.,China

冰川融水径流的发育和形成过程中,存在大量水化学侵蚀,尤其是K/Na长石及碳酸盐的水解作用,可能消耗水体中H+,促使大气CO_2溶于水形成重碳酸盐,影响区域碳循环。2015年7月21日—2017年7月18日选取相对平坦开阔的西天山科其喀尔冰川表碛物覆盖区,利用涡度相关法进行CO_2通量监测。结果表明:大气CO_2通量介于-17. 99～3. 59 g·m^(-2)·d^(-1)之间,平均值为-2. 58 g·m^(-2)·d^(-1),说明研究区是一个显著的碳汇。净冰川区系统CO_2交换量主要受大气CO_2通量支配,但日内变化显著,白天因冰雪消融导致大气CO_2沉降于融水中促进区域水化学侵蚀,而夜间因太阳辐射减少,冰雪消融减弱甚至停止,抑制了区域CO_2沉降,甚至再生冰的形成引起溶解于液态水中的CO_2释放。净冰川区系统CO_2交换量与气温呈显著的负相关关系,即气温升高,大气CO_2沉降量增加;当降水量小于8. 8 mm时,交换量随降水量变化不显著,而降水量大于8. 8 mm时,CO_2沉降量随降水量增加而减少。净冰川区系统CO_2交换量随日径流量的变率遵循:积雪消融期>积雪积累期>冰川消融前期>冰川消融后期>冰川消融峰期,意味着积雪消融存在时,系统CO_2交换量随日径流量变率较大,可能是因积雪本身的阻尼作用或积雪期水文通道不发育,积雪融水较冰川冰融水汇集相对较慢,为可溶性物质化学反应提供充分时间,增强了CO_2沉降。

The hydrolysis of Na,K,Ca feldspar and carbonate in surface runoff consumed a mass of H^+ ,which would cause atmospheric CO2 to sink.In the glacier area,the CO2 flux at the gas-liquid interface was usually analyzed using the method of hydrochemical mass balance.In recent years,the eddy covariance systems have been used to analyze energy balance,CO2flux and moisture flux in the areas of complex terrain.In this study,the CO2flux was monitored by eddy covariance system in the Koxkar glacier of the Western Tianshan,Xinjiang,China from 2015to 2017,and the results showed that the CO2fluxes were ranged from -17.99to 3.59g·m^-2·d^-1 with an average of -2.58g ·m^-2·d^-1.The CO2flux values were negative in the January (-0.21g ·m^-2·d^-1).It indicated that atmospheric CO2sank on the glacier area because of the dissolved CO2in the water when the interaction between the water and the rock occurred during precipitation/snow and ice melting.Further analysis suggested that the net glacier exchange (NGE) of CO2was decreased as the daily temperature increased.There was a significant negative correlation between NGE and daily temperature.For precipitation,almost no effect on the NGE was found when the precipitation was less than 8.8mm.However,the daily NGE was decreased exponentially with the increase of precipitation when the precipitation was greater than 8.8 mm.The effect of precipitation on CO2 absorption was mainly reflected in the following two aspects.One was the CO2sink at the gas-liquid interface slow down resulting from the weakening of the water chemical erosion caused by the reduction of the ice melting,which caused by continuous heavy rain reducing the temperature.The other was the CO2sink at the gas-liquid interface was decreased due to the increasing dissolving CO2in the atmosphere because of increasing of the precipitation.Finally,there were significant linear relationships between the NGE and the runoff.However,the slopes of linear relationships between the NGE and the runoff varied during different periods,which were due to changes in the type of hydrochemical reaction caused by changes of effective ablation area,and changes in hydrochemical reaction time effected by the hydrological channels below the ice.