北极楚科奇海海冰特征研究——以1999年夏季为例

The Characteristics of Summer Sea Ice and Their Relationship with Climate in the Chukchi Sea

对北冰洋楚科奇海海冰分布、厚度、气 /冰 /海界面温度场观测 ,钻取海冰冰芯 ,观测冰结构的变化 ,发现 3种海冰组合结构 :1)表面融化型 ;2 )表面和底部融化型 ;3)整体融化型 .海冰结构形成的热力学过程为 :在气 /冰界面上 ,海冰上表面吸收辐射能使冰体升温 ,出现表面融化 ;在冰 /海水界面上 ,海冰盘与开阔水域的相间分布、相对运动 ,将周围温度较高的水体输送到海冰的底部 ,加热、融化海冰底部 ;冰体升温 ,冰晶间盐水膜首先融化 ,分离冰晶 ,破坏海冰整体结构 .冰的相变吸热 ,使其温度维持在融点 。

Sea ice is the main surface feature of the Arctic Ocean. Sea ice greatly influences the climate in the Arctic. Previous researches showed that the climate change in Arctic during the past 40 a was in disaccord with other areas, especially in summer. It could be the sea ice process, which restricts the effect of global warming on the Arctic Ocean. During August 1999, a sea ice investigation was taken in the Chukchi Sea by the Chinese National Arctic Expedition. Investigation items included sea ice characteristics, such as its distribution, surface features, thickness and floe movement, and temperature fields around the interfaces of air/ice/seawater. Thirteen ice cores were extracted from 11 floes in the area of 72°24′ ～ 77°18′ N and 153°34′ ～ 163°28′ W. Their structures were observed.Three melting processes of ice were observed: surface layer melting, both surface and bottom layers melting and full melting. The observed temperature fields around floes showed that the bottom melting under floes was an important process. As alternate distribution of floes and open water in the summer Arctic Ocean and large surface albedo difference between ice, about 66% ～ 90%, and water, only 5% ～ 10%, the water under ice was colder than the open water by 0.4 ～ 2.8℃. Radiation heated seawater in open water areas and then the warmer water flowed into the ice bottom directly when the floes moved to these areas. This caused melting under the bottom of floe. This process effectively counterbalances the warm wave in all of the Arctic Ocean in summer, thus counteracts the global warming effect in the Arctic Ocean. From the observed structures of sea ice cores, it can be seen that sea ice was composed of ice crystals and brine films. During the ablation period, the brine films between ice crystals melted firstly, then the ice crystals were encircled by the brine-water films, finally the sea ice became a mixture of ice and water, with an ice structure of ice skeleton full of meltwater. At the end of the ablation period, the crystals would be separated each other. At that time, the link between ice crystals greatly decreased. This kind of ice floe would collapse rapidly at the end of ablation.