Provenance and transport of supraglacial debris revealed by variations in debris geochemistry on Khumbu Glacier, Nepal Himalaya
Provenance and transport of supraglacial debris revealed by variations in debris geochemistry on Khumbu Glacier, Nepal Himalaya
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DOI：
10.1002/esp.5657
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发表时间：
2023-07
影响因子：
3.3
通讯作者：
M. Kirkbride;S. C. Sherriff;A. Rowan;D. Egholm;D. Quincey;E. Miles;B. Hubbard;K. Miles
中科院分区：
文献类型：
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作者：
M. Kirkbride;S. C. Sherriff;A. Rowan;D. Egholm;D. Quincey;E. Miles;B. Hubbard;K. Miles
冰上碎屑覆盖物的起源通常被概念化为缓慢移动的冰中的冰内碎屑融化形成的表面滞后，其中复杂性来自碎屑厚度和子碎屑冰融化之间的反馈。在这里，我们从碎片来源和高海拔复合山谷冰川中不断变化的支流供应的角度来研究碎片覆盖层的起源。从6个支流的昆布冰川（尼泊尔）的21个碎片样品中的11个主要元素的地球化学分析显示明确的统计差异的碎片来源，反映支流集水区之间的岩性差异。使用FR 2000沉积物分解模型，根据其源区对来自消融区横断面的24个样本进行分区。我们估计年龄的冰在每个样带使用高阶冰流模型。结果表明，在经历了较长的出油管历史的冰川下游位置，来自侧支流的碎片比例更大。最近，来自喜马拉雅山脉主分水岭（西Cwm）的冰变得相对更加重要。这表明，在较低的冰川的结构状态的变化取决于相对冰排放的横向和分裂源。来自低海拔支流的冰通量可能在公元1420年左右印度夏季风减弱之前更为重要。海拔较低的支流位于晚全新世平衡线海拔变化的范围内，因此对冰川流动结构的气候驱动因素反应最敏感。自公元1900年左右以来的负冰川物质平衡导致支流冰川分离，高海拔集水区重新成为昆布冰川的主要冰源。
The origin of supraglacial debris covers is often conceptualised as the formation of a surface lag by melt‐out of englacial debris from slow‐moving ice, where complexity arises from feedback between debris thickness and sub‐debris ice melt. Here, we examine the origin of a debris cover from the perspective of debris provenance and changing tributary supply in a high‐elevation compound valley glacier. Geochemical analysis of 11 major elements in 21 debris samples from six tributaries of Khumbu Glacier (Nepal) shows unambiguous statistical differentiation of debris sources reflecting lithological differences between tributary catchments. Twenty‐four samples from transects across the ablation area are partitioned according to their source areas using the FR2000 sediment unmixing model. We estimate the age of ice at each transect using a higher order ice flow model. The results show greater proportions of debris from lateral tributaries in downglacier locations that have experienced longer flowline histories. More recently, ice from the Main Himalayan Divide (Western Cwm) has become relatively more important. This suggests a change in the state of the lower glacier's structure depending on the relative ice discharges of lateral and divide sources. Ice flux from lower elevation tributaries was more important probably prior to a weakening of the Indian Summer Monsoon at around 1420 CE. The lower elevation tributaries lie within the range of late Holocene equilibrium line altitude variation and therefore respond most sensitively to climatic drivers of the glacier's flow structure. Negative glacier mass balance since around 1900 CE caused tributary glaciers to detach and high‐elevation catchments to re‐establish as the dominant ice source to Khumbu Glacier.