念青唐古拉山扎当冰川雪冰中不溶性有机碳含量及其辐射强迫研究

为了研究雪冰中不溶性有机碳(Water-insoluble Organic Carbon,WISOC)的含量及其辐射强迫作用,于2012年7月和8月对青藏高原南部纳木错流域扎当冰川90个表层雪冰样品中WISOC的含量进行了分析,采样期间利用地物光谱仪实地测量了反照率.结果表明,在消融季节(7—8月),扎当冰川表面被裸冰、老雪和新雪覆盖,以上3种消融情形下WISOC的平均含量分别为(1618.4±1236.0)、(432.3±329.7)和(183.7±158.0)ng·g-1,雪冰的融化导致WISOC等吸光性物质在冰川表面的富集,降低了冰川表面反照率.通过SNICAR模型(Snow,Ice,and Aerosol Radiative Modle)敏感性分析表明,3种情形下WISOC降低雪冰表面反照率(贡献率)分别为0.0020(6.8%)、0.0018(7.4%)和0.0010(2.1%),对应的WISOC的辐射强迫分别为1.14、1.34和0.81 W·m-2.平均地,WISOC对辐射强迫的影响超过了黑碳(BC)影响的20%,而在新雪覆盖条件下,WISOC对辐射强迫的影响甚至达到了粉尘影响的72.3%.因此,虽然雪冰中的WISOC的吸光能力相对于BC较弱,但所引起的雪冰表面反照率降低及冰川消融等效应不容忽视.

Concentration and radiative forcing of water-insoluble organic carbon of Zhadang glacier on western Nyainqentanglha

In order to analyze the concentration of water-insoluble organic carbon (WISOC) in snow/ice and its effect on the radiative forcing, a total of 90 surface snow/ice samples from Zhadang glacier in the southern Tibetan Plateau were collected during the summer of 2012. Concentration of WISOC was analyzed using a thermal-optical method and albedo was measured using Analytical Spectral Devices (ASD) spectrometer. During melting season, the glacier surface is usually covered by bare ice, aged and fresh snow. Average WISOC concentrations were (1618.4±1236.0), (432.3±329.7) and (183.7±158.0) ng·g^-1 in three melting cases respectively. The melting of glacier resulted in the enrichment of WISOC and other light absorbing particles, thus reducing the snow/ice surface albedo. Sensitivity analysis using SNICAR model showed that the albedo reduction (contributions) caused by WISOC were 0.0020 (6.8%), 0.0018 (7.4%) and 0.0010 (2.1%), respectively. The radiative forcing exerted by WISOC was found to be 1.14, 1.34 and 0.81 W·m^-2 respectively for three cases. On average, albedo reduction caused by WISOC was over 20% of that by black carbon, especially when the surface was covered by fresh snow. The influence of WISOC on the radiative forcing was even up to 72.3% of that by dust effect. Although the absorption ability of WISOC was weaker than BC, it cannot be ignored that WISOC would cause snow/ice surface albedo reduction and glaciers melting. Therefore, this study will gain a better understanding of the optical absorption material in the glaciers and water resources on the Tibetan Plateau.