南极洲乔治王岛柯林斯冰帽冰芯层位和密度变化的一般特征

GENERAL CHARACTERISTICS IN STRATIGRAPHY AND DENSITY VARIATION FOR ICE CORES FROM COLLINS ICE CAP, KING GEORGE ISLAND,ANTARCTICA

柯林斯冰帽两支冰芯层位记录证实了该冰帽主冰穹顶部（海拔约７００ｍ）属暖渗浸带，小冰穹顶部（海拔约２５０ｍ）属渗浸带。雪、冰的层位分布和密度变化包含了一定的测年信息。主冰穹顶冰芯密度－深度曲线在表层呈现韵律性变化，与层位记录中的融化冻结现象相对应，据此粗略划分年层，断定当地年积累雪层厚度为３－３．５ｍ，折合水当量１６５０－１９２５ｋｇ／ｍ２ａ，年平均积累速率约为２．０ｍ／ａ（冰当量）。主冰穹顶成冰深度为３８－３９ｍ，此深度以上密度自上而下缓慢增加，但以下由于含水层的出现，密度迅速升高，在５－６ｍ区间达到９００ｋｇ／ｍ３。小冰穹冰芯除表层外，密度基本在８００－９００ｋｇ／ｍ３之间，冰芯中雪冰互层，存在污化面，４０ｍ以下发现很厚的火山灰沉积物。小冰穹平均年积累率约为０．７ｍ／ａ（冰当量），成冰深度７－８ｍ。

It was proven by the stratigraphy of two ice cores from Collins Ice Cap that the summit of Main dome(with elevation of 700m or so) belongs to warm infiltration zone,while that of Small dome(with elevation of 250m or so)to infiltration zone.A certain dating information could be found from the distribution of snow and ice layers along the ice core. The curve of density against depth for the ice core from the summit of Main dome showed regular variation corresponding to the distibution of melt features in stratigraphic record.The annual layers was roughly determined consequently.It was estimated that the accumulation rate in snow thickness at the summit of Main dome was 3-3.5m,which was about 1650-1925kg/m 2·a in water equivaleat and 2.0m/a in mean ice thickness equivalent.The transition depth of snow to ice there was 38-39m, above it density increased gradually downward,but at rather high rate below that depth, due to appearance of water table, reaching 900kg/m 3 in 5-6m interval.The density data of the ice core from the summit of Small dome showed the fluctuation between 800 and 900kg/m 3 except that of the very surface part, in which the snow and ice interleaved frequently and dust layers existed.These suggested that the accmulation rate at the summit of Small dome was about 0.7m/a in ice equivalent and the transition depth of snow to ice is 7-8m,covering about 10 year's mass cumulated.Very thick volcanic deposition layers were discovered at the depth below 40m in the ice core from the the summit of Samll dome.