东南极冰盖内陆深处几个雪坑离子浓度的初步研究

A Primary Study on Ionic Concentrations in Snow Pitsin the Hinterland of East Antarctica

对南极中山站-DomeA断面距海岸800～1100km(海拔2850～3760m)的内陆深处3个雪坑进行了雪层剖面观测和雪样化学分析.氧同位素、可见层位特征与主要阴、阳离子浓度的剖面对比分析表明,同位素季节变化信号不明显,而太阳辐射冰壳与某些离子(如Na+、Cl-等)浓度变化有较好的对应.研究区域主要的几种离子如Na+、Cl-和SO2-4等与东南极内陆其它区域雪坑中的相似,但NO-3和NH+4有较大差异.在高原中心区域,NO\+-3沉积后很大部分又逸散返回大气,因而雪层中平均浓度很低但表面处的浓度却异常地高.在海拔2850m处,各种离子的浓度随深度增加而增加,在海拔3750m处则为相反趋势,在海拔3380m处趋势不明显.如果离子沉降速率保持不变,这种特征意味着近20a来降雪积累速率在高原中心区域为减少趋势,在海拔较低的区域则为增加趋势.在所有雪坑中,Na+和Cl-具有非常好的正相关性,Cl-/Na+为1.24～1.61,略高于海水中的值(1.168),说明Cl-虽然主要来源与于海盐,但仍有一小部分为其它来源.非海盐SO2-4在不同雪坑中显示出不同特征,对其是否能指示火山喷发等问题还有待于进一步探讨.

During an inland traverse expedition along the route from Zhongshan Station to Dome A in East Antarctica in 19981999, three snow-pits with a depth range of 2.1 to 3.3 m were dug and sampled continuously at the sites 800～1100 km away from the coast and between 2850 m and 3760 m a.s.l. The samples have been analyzed for stable oxygen isotope and major ions. Since seasonal change in {δ~{18}O} is not clear, the initial dating was made through comparison of concentration profiles of major ions and then adjusted according to visible stratigraphy. Average concentrations of most ions in the snow-pits are close to those at other sites in East Antarctic Plateau, but NH~{4+} and NO~{3-} are quite different. In the central part of the plateau, a large part of NO~{3-} is lost by re-emission back to atmosphere after deposited so that its concentration is very low on an average in all depths but extremely high at surface. Ionic concentrations have an increase trend with depth at lower altitudes but it is opposite at 3760 m a.s.l., perhaps, hinting a regional difference in change of the snow accumulation, i.e. the accumulation rate has decreased near the plateau top and increased in the lower altitudes in the past two decades. In all the snow-pits, concentration profiles of Na^+ and Cl^- have a very good positive correlation. The ratio of Cl^- to Na^+ is 1.24～1.61 in μeq·L~{-1}, a little higher than that in seawater (1.17), implying that Cl^- has multiple origins, although its major part is from sea salts. Profiles of nssSO~{2-}-4 in the pits have quite different features and so it is questionable if them could be used to identify volcanic eruptions.