ABSTRACT Subglacial glaciohydraulic supercooling can form basal ice and affect glacier dynamics, sediment transfer and geomorphology. Whilst isotopic analysis (δ18O-δD) of basal ice has demonstrated the significance of supercooling, questions remain as to what extent the identification of supercooling depends on sampling resolution. We conducted laboratory experiments in which ice was frozen from supercooled water and sampled at a micro-scale (1.5 millilitre) to identify highly localized variations in isotopic compositions that might be lost in bulk-scale sampling. Three distinctive ice facies produced by the freezing process demonstrated diagnostic isotopic signatures that were distinguished when the facies were sampled independently. However, their respective isotopic signatures were lost when bulk-scale sampling combined the two facies, demonstrating the requirement of micro-scale sampling when identifying supercooling in basal ice facies. These findings indicate that sampling for isotopic compositions of ice facies frozen from supercooled water should be conducted at a scale that prevents the amalgamation of different facies to highlight a detailed isotopic signature. We conclude that micro-scale sampling is imperative to understanding and quantifying this subglacial process.

中文翻译：

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过冷水冻结冰相的微尺度同位素分析

摘要 冰下冰川水力过冷可形成基底冰，影响冰川动力学、沉积物迁移和地貌。虽然基底冰的同位素分析 (δ18O-δD) 已证明过冷的重要性，但仍然存在问题，即过冷的识别在多大程度上取决于采样分辨率。我们进行了实验室实验，其中冰从过冷水中冷冻并以微尺度（1.5 毫升）取样，以识别可能在批量取样中丢失的同位素组成的高度局部变化。由冷冻过程产生的三个独特的冰相显示出诊断同位素特征，当这些相独立取样时这些特征可以区分。然而，当批量采样结合这两个相时，它们各自的同位素特征丢失了，证明了在识别基底冰相过冷时对微尺度采样的要求。这些发现表明，从过冷水中冻结的冰相同位素组成的采样应该以防止不同相融合的规模进行，以突出详细的同位素特征。我们得出结论，微尺度采样对于理解和量化这一冰下过程至关重要。