南极纳拉海峡固定冰生长、结构、盐度和氧同位素组成

The Growth,Structure,Salinity and δ^(18)O of Landfast Sea Ice in Nella Fjord,Antarctica

采用第19次中国南极科考采集的冰芯样品、数据,基于海冰的"冻结日"记录,使用海冰一维热力学模型来计算纳拉海峡固定冰的生长厚度.考虑气象条件以及冰情观测结果,将该模型的计算海冰厚度和实测厚度进行比较发现,在纳拉海峡存在着多年生长的海冰.对采集于南极洲中山站附近纳拉海峡的固定冰冰芯样品进行结构、盐度和稳定氧同位素(δ18O)分析,获取了海冰的结构和盐度剖面特征、冰芯雪冰、附加冰的含量、雪冰中的雪以及全部冰芯中雪所占的百分比.结果表明:样品冰芯具有典型的海冰特征结构,如柱状冰水平方向的C轴以及上部粒状冰层和下部柱状冰层结构特征,部分柱状冰中间存在着粒状冰夹层;盐度和δ18O剖面也显示了多年冰生长的证据.海冰的结构和氧同位素特征表明,纳拉海峡固定冰的生长主要受热力学过程控制,其结果和2000年1月至2003年2月人工冰情观测结果一致,观测中没有发现冰脊、叠置等动力过程.附加冰在冰芯中所占的比例平均为5.01%.使用不同的同位素标准来区分雪冰层,估计研究区域平均有多达16.4%～37.9%的雪冰,海冰粒状层中雪的部分约占全部冰厚度的0.8%～23.5%.

Research on sea ice physical characteristics is the principal means to understand the sea ice formation process. By the 19th Chinese Antarctic Research Expedition, the 1-D thermodynamic sea ice model based on freezing degree day was used to estimate the landfast sea ice development in Nella Fjord. Comparing the modeled ice thickness with the measured ice thickness, in relation to atmospheric condition as well as visual observations of ice condition, it is found that multiyear ice has developed in Nella Fjord. The structure, salinity and stable oxygen isotopic properties of the samples collected on the landfast sea ice were also used to study the features of ice textural and salinity profiles, the contribution of snow-ice to total sea ice thickness, the percentage of superimposed ice, and the fraction of snow in the snow-ice layers and in the total sea ice thickness in Nella Fjord. The structure analysis of the sea ice cores reveals that there are a general structure of horizontal c-axis in columnar ice, a granular surface layer and a columnar basal layer with a ＂buried＂ granular ice layer between two columnar ice layers. Both the salinity profiles and δ^18O profiles show the multiyear ice developing in Nella Fjord. The textural and isotopic properties of sea ice indicate that the thermodynamic mechanisms are responsible for the development of the landfast ice in Nella Fjord. The results are well agreement with the visual observations of sea ice conditions between Jan 2000 to Feb 2003. No ridging and rafting can be seen. The ratio of the superimposed ice to the total ice thickness is 5.01 % on the average. Using different isotopic criteria to distinguish snow-ice layers, the ratio of snow-ice layers to the total ice thickness is estimated from 16.4 to 37.9% on average in the study region. The ratio of snow in the granular ice layers to the total sea ice thickness （by mass） is estimated from 0. 8% to 23. 5%.