Air Mixing in Firn and the Age of the Air at Pore Close-Off
Air Mixing in Firn and the Age of the Air at Pore Close-Off
复制标题
冷杉中的空气混合和毛孔关闭时的空气年龄
DOI：
10.3189/s0260305500004328
复制
发表时间：
1988
影响因子：
2.9
通讯作者：
A. Sigg
中科院分区：
文献类型：
--
作者：
J. Schwander;B. Stauffer;A. Sigg
被困在天然冰泡中的空气与周围的冰的年龄不同。这是因为空气只有在冰雪过渡的深度才被封闭在孤立的气泡中。在覆盖的多孔降雪层内，空气能够与大气进行一定程度的混合和交换。冰和空气之间的年龄差是由冰在气孔关闭时的年龄减去混合延迟得出的。此外，由于扩散平滑和冰雪过渡时空气的逐渐封闭，也存在年龄分布。了解这种年龄关系对于解释在冰芯上测量的气候参数是必要的。这项工作集中在扩散混合的影响。本文报道了南极Siple站积雪样品中CO2和O2扩散系数的测量结果。结果表明，混合过程以分子扩散为主。扩散系数与孔隙率近似成线性关系。用一维扩散模式计算了南极西普勒站、南极克雷特站和格陵兰克雷特站降雪中的空气混合。获得了10到50年的交换时间。
The air trapped in the bubbles of natural ice is not the same age as the surrounding ice. This is due to the fact that the air is enclosed in isolated bubbles only at the depth of the firn–ice transition. Within the overlying porous firn layer the air is able to mix and to exchange to a certain degree with the atmosphere. The age difference between ice and air is given by the age of the ice at pore close-off, less the mixing delay. Also, there is an age distribution due to diffusive smoothing and due to the gradual enclosure of the air at the firn–ice transition. Knowledge of this age relation is necessary for the interpretation of climatic parameters measured on ice cores. This work concentrates on the effect of diffusive mixing. We report on measurements of the diffusivity of CO2 and O2 (in N2) in firn samples from Siple Station, Antarctica. It is shown that the dominant mixing process is molecular diffusion. The diffusion coefficient depends approximately linearly on the porosity. A one-dimensional diffusion model has been used to calculate the air mixing in firn at Siple Station (Antarctica), at the South Pole, and at Station Crête (Greenland). An exchange time of between 10 and 50 years is obtained.