Interal Distribution of Acid Material within Snow Crystals

我们发现，日本的河水不仅在融雪期的第一阶段，而且在后期都是酸性的，这与北方欧洲融雪期第一阶段所报道的所谓酸冲击不同，酸冲击取决于融化-再冻结过程的区域特征，从而形成雪晶内部酸性物质的分布。在日本南部这样的温暖气候地区，由于在温暖变质作用下长期反复的熔融-再冻结过程，有可能在颗粒雪中具有复杂的酸性物质分布结构。因此，融雪水的pH值并不总是随着融雪的进行而增加。然后，我们通过X射线计算机断层扫描（CT扫描仪）阐明了酸性物质在雪晶内部的微观分布结构，即在雪晶内部也存在含有酸性物质的区域。因此，即使在融雪的后期，当酸性物质集中在雪晶内部时，河水的酸化也会发生。

We found that the river water turns out to be acid not only in the first stage but also in the later stage of snowmelt season in Japan, which differs from the so called acid shock reported to occur in the first stage of the sonwmelt in the northern Europe.The acid shocks depend on the regional characteristics of the melt-refreeze processes forming the internal distribution of acid materials within snow crystals. In a warm climatic region like the southern Japan, there are possibilities to have the complicated distribution structure of acid materials within granular snows due to the repeated melt-refreeze processes for a long period under the warm metamorphism. Consequently, the pH value of melt water does not always increase as the snowmelt proceeds.Then, we clarified the microscopic distribution structure of acid materials within snow crystals by using the X-ray computed tomography (CT scanner) that the domains with the acid materials do also exist in the inner parts of snow crystals. So, the acidification of the river water occurs even in the later stage of the snowmelt, when the acid materials concentrates in the inner part of snow crystals.