Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide deep ice core site
Rapid and accurate polarimetric radar measurements of ice crystal fabric orientation at the Western Antarctic Ice Sheet (WAIS) Divide deep ice core site
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DOI：
10.5194/tc-2020-264
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发表时间：
2020-09
期刊：
影响因子：
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通讯作者：
T. J. Young;C. Martín;P. Christoffersen;D. Schroeder;S. Tulaczyk;E. Dawson
中科院分区：
文献类型：
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作者：
T. J. Young;C. Martín;P. Christoffersen;D. Schroeder;S. Tulaczyk;E. Dawson
抽象。冰盖的晶体取向组构记录了过去冰盖的变形历史，并影响着现今的冰流动力学。虽然没有广泛实施，相干探冰雷达能够检测各向异性COF模式，利用双折射的冰晶在雷达频率。大多数以前的雷达研究量化COF在一个粗略的方位分辨率有限的观测数量与一对天线沿着采集平面，围绕一个方位中心旋转。在这项研究中，我们反而进行了一套四极化测量组成的四个正交天线方向组合在南极西部冰盖（WAIS）划分深冰芯网站。通过这些测量，我们能够以高达1°和15 m的方位角和深度分辨率量化该站点至1500 m深度的COF。我们对结构不对称性的估计与直接从WAIS分水岭深冰芯测量的相应结构估计密切匹配。虽然冰芯研究往往无法确定绝对的结构方向，由于核心旋转提取过程中，我们能够明确地确定和得出结论，结构方向是深度不变的至少1500米，相当于7400年BP（1950年之前），并完全符合现代表面应变方向在WAIS分水岭。我们的研究结果支持的说法，在WAIS分水岭的变形制度并没有发生实质性的变化，通过大部分的全新世。快速偏振测定散装COF比较以及更费力的样品为基础的COF测量从薄冰部分。因为它是前者，最终影响冰流，这些偏振雷达方法提供了一个机会，准确和广泛的散装COF映射和纳入冰流模型。
Abstract. The Crystal Orientation Fabric (COF) of ice sheets records the past history of ice sheet deformation and influences present-day ice flow dynamics. Though not widely implemented, coherent ice-penetrating radar is able to detect anisotropic COF patterns by exploiting the birefringence of ice crystals at radar frequencies. Most previous radar studies quantify COF at a coarse azimuthal resolution limited by the number of observations made with a pair of antennas along an acquisition plane that rotates around an azimuth centre. In this study, we instead conduct a suite of quad-polarimetric measurements consisting of four orthogonal antenna orientation combinations at the Western Antarctic Ice Sheet (WAIS) Divide Deep Ice Core site. From these measurements, we are able to quantify COF at this site to a depth of 1500 m at azimuthal and depth resolutions of up to 1° and 15 m. Our estimates of fabric asymmetry closely match corresponding fabric estimates directly measured from the WAIS Divide Deep Ice Core. While ice core studies are often unable to determine the absolute fabric orientation due to core rotation during extraction, we are able to unambiguously identify and conclude that the fabric orientation is depth-invariant to at least 1500 m, equivalent to 7400 years BP (years before 1950), and coincides exactly with the modern surface strain direction at WAIS Divide. Our results support the claim that the deformation regime at WAIS Divide has not changed substantially through the majority of the Holocene. Rapid polarimetric determination of bulk COF compares well with much more laborious sample-based COF measurements from thin ice sections. Because it is the former that ultimately influences ice flow, these polarimetric radar methods provide an opportunity for accurate and widespread mapping of bulk COF and its incorporation into ice flow models.