Ground ice recharge via brine transport in frozen soils of Victoria Valley, Antarctica: insights from modeling δ18O and δD profiles.
Ground ice recharge via brine transport in frozen soils of Victoria Valley, Antarctica: insights from modeling δ18O and δD profiles.
复制标题
南极洲维多利亚谷冻土中通过盐水输送进行地冰补给：δ18O 和 δD 剖面建模的见解。
DOI：
10.1016/j.gca.2009.10.021
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发表时间：
2010
影响因子：
5
通讯作者：
E. Steig
中科院分区：
文献类型：
--
作者：
B. Hagedorn;R. Sletten;B. Hallet;D. Mctigue;E. Steig
南极洲麦克默多干谷的土壤含有冰和大量的盐。在整个干谷和其他极度干旱的永久冻土地区，特别是在火星上，冰经常出现在浅层。浅层冰的这种常见现象令人费解；然而，根据已发表的升华模式，由于蒸汽损失到大气中，它应该相对较快地消失（以0.1毫玛−1数量级的速率）。这种损失可由融雪渗透和冻结在土壤中的补给所抵消。本文基于实测的δD和δ18O垂直剖面，首次提出了这种补给的定量估计，这些剖面揭示了冰源和冰汇的相当详细的信息。我们对这些剖面进行了建模，考虑了南极洲维多利亚谷约10ka年龄的冰固化土壤沿1.6m深度剖面的盐含量和土壤温度记录。冰稳定同位素在冰胶结体顶部（20cm深度）以重同位素富集；δD和δ18O值随深度的变化均呈上凹曲线。在深部，其同位素组成与维多利亚湖和现代大气水相似。同位素剖面的凹形暗示了富含重同位素的融雪水向下平流扩散进入冰胶结体。我们的平流-弥散模型与现场数据相结合，使我们能够量化融水进入冰的平流通量和弥散。平流速度和频散系数取决于平流开始时间和冰卤比；它们的数量级分别为10−11-10−10ms−1和10−12-10−11m2s−1。这些数值表明，在~ 10ka的时间内，总共有190mm的水渗入冰固化的地面。利用开放系统-瑞利分馏，可以用富盐融雪水模拟最上层冰水泥的同位素组成和氘过量值。要形成上部冰水泥的同位素特征，需要蒸发约95%的融雪水。以190毫米的盐水渗入土壤为基础，初始总共需要约4米的融雪水。这相当于~ 0.4mma−1，这表明，在当前气候条件下，融雪产生的水足以补偿模拟的升华率，从而保护维多利亚谷的地面冰。
Soils in the McMurdo Dry Valleys, Antarctica contain ice and considerable amounts of salt. Ice often occurs at shallow depth throughout the Dry Valleys and other areas of hyperarid permafrost, notably on Mars. This common occurrence of shallow ice is enigmatic; however, since according to published sublimation models it should disappear relatively quickly (at rates of order 0.1mma−1) due to vapor loss to the atmosphere. This loss may be offset by recharge from snowmelt infiltrating and freezing in the soil. Herein, we present a first quantitative estimate of this recharge based on measured vertical profiles of δD and δ18O that reveal considerable detail about the sources and sinks of ice. We model these profiles, taking into account the salt content and a soil temperature record along a 1.6m depth profile of ∼10ka old ice-cemented soils in Victoria Valley, Antarctica. The stable isotopes of ice are enriched in heavy isotopes at the top of the ice cement (20cm depth); both δD and δ18O values plotted against depth exhibit a concave upward curve. At depth, the isotope composition is similar to that of Lake Victoria and modern meteoric water. The concave shape of the isotope profile is suggestive of downward advection–dispersion of snowmelt water enriched in heavy isotopes into the ice cement. Our advection–dispersion model, coupled with field data, enables us to quantify the advective flux and dispersion of melt water into the ice. The advective velocity and dispersion coefficient depend on the time since advection began and the ice-to-brine ratio; they are, respectively, of the order of 10−11–10−10ms−1and 10−12–10−11m2s−1. These values suggest that over the ∼10ka time period, a total of 190mm water infiltrated into the ice-cemented ground. The isotope composition and deuterium excess values of the uppermost ice cement can be modeled from snowmelt water enriched in salts using open system-Rayleigh fractionation. To develop the isotopic signature of the upper ice cement requires evaporation of ∼95% of the snowmelt water. Based on 190mm brine infiltrating into the soil requires an initial total of ∼4m of snowmelt water. This corresponds to ∼0.4mma−1suggesting that, under the current climate condition, water from snowmelt is sufficient to compensate modeled sublimation rates, and therefore conserve ground ice in Victoria Valley.