冰芯中MSA迁移假说的延伸和完善

EXTENSION AND THEORETICAL IMPROVEMENT OF A HYPOTHESIS FOR MSA MIGRATION IN ICE CORES

MSA在冰芯深层的“迁移”现象的存在 ,关系到能否应用大气中 MSA季节特征进行极地冰芯断代 ,并以冰芯分析结果确定大气中生物硫化物含量的方法基础。本文展示各类最有代表性的冰雪 MSA剖面 ,对提出冰芯深层 MSA“迁移假说”的理论依据进行探讨 ,并根据最新资料 ,说明冰川中 MSA的“迁移”和重新分布 ,在表层粒雪和渗浸 -冻结冰层中同样可能发生。对“迁移假说”的延伸补充在于 ,粒雪中的 MSA迁移是在积雪中空气与外界贯通的“开放”条件下进行的 ,渗入雪层中的融水将 MSA溶出后 ,在晶粒间宏观向下输送 ,在阳离子集中的层位发生反应 ,生成盐类冰点的改变使之发生“冻结”,重新分布。而渗浸 -冻结冰层中的迁移机制可能和深层冰川冰中的情况接近 ,即在气体与外界隔绝条件下 ,主要在“封闭”的晶间脉状纹理中以“微观”形式进行。南极半岛 MSA迁移过程需要很长时间 ,而表层渗浸 -冻结冰层中 MSA迁移过程很快出现 ,说明冰中脉状纹理的加快形成、较高冰川温度和冰层中的较大含水量等因素会对 MSA“迁移”进程起促进作用。最后 ,对 MSA“迁移”情况下 ,如何进行有关冰芯 MSA计算进行了讨论 ,对设计实验验证并完善迁移理论提出了设想。

The most representative MSA profiles of snow/ice in the sense of migration were exhibited. The principle on which the hypothesis of MSA migration was drawn out was examined. The update data show that the mechanism responsible for MSA migration and relocation supposed for the deeper part of the ice cores could also work for the firn and infiltration congelation ice on the glacier surface. The extension given to the hypothesis by new evidences is that the migration of MSA in the firn is carried out in the open environment where air is connecting with the atmosphere. MSA in resolute is moving downwards, among grains, till the depth where cations are highly concentrated and salts could be formed via combination. It is, quite possibly, the relatively higher freezing point of newly formed methanesulphate salts (e.g. of Na + or of Mg 2+ ) that makes MSA “refrozen” and relocated. The mechanism for the migration of MSA in the infiltration congelation ice is, perhaps, the same for the deeper part of the glacier ice. The comparison of time spent on MSA migration in deeper glacier ice of Antarctic Peninsula and that in the surface infiltration congelation ice of mid latitude glacier suggests that the quick formation of interlinked network of veins in ice, higher temperature and more water content of the ice probably may sever as the promoting factors for the MSA migration. Finally the related calculation referring to the MSA migration, the experiments to verify the hypothesis in lab and problems in the improvements of the migration theory were discussed.