DataSheet1_Evolution of Surface Characteristics of Three Debris-Covered Glaciers in the Patagonian Andes From 1958 to 2020.docx

A number of glaciological observations on debris-covered glaciers around the globe have shown a delayed length and mass adjustment in relation to climate variability, a behavior normally attributed to the ice insulation effect of thick debris layers. Dynamic interactions between debris cover, geometry and surface topography of debris-covered glaciers can nevertheless govern glacier velocities and mass changes over time, with many glaciers exhibiting high thinning rates in spite of thick debris cover. Such interactions are progressively being incorporated into glacier evolution research. In this paper we reconstruct changes in debris-covered area, surface velocities and surface features of three glaciers in the Patagonian Andes over the 1958–2020 period, based on satellite and aerial imagery and Digital Elevation Models. Our results show that debris cover has increased from 40 ± 0.6 to 50 ± 6.7% of the total glacier area since 1958, whilst glacier slope has slightly decreased. The gently sloping tongues have allowed surface flow velocities to remain relatively low (<60 m a−1) for the last two decades, preventing evacuation of surface debris, and contributing to the formation and rise of the ice cliff zone upper boundary. In addition, mapping of end of summer snowline altitudes for the last two decades suggests an increase in the Equilibrium Line Altitudes, which promotes earlier melt out of englacial debris and further increases debris-covered ice area. The strongly negative mass budget of the three investigated glaciers throughout the study period, together with the increases in debris cover extent and ice cliff zones up-glacier, and the low velocities, shows a strong linkage between debris cover, mass balance evolution, surface velocities and topography. Interestingly, the presence of thicker debris layers on the lowermost portions of the glaciers has not lowered thinning rates in these ice areas, indicating that the mass budget is mainly driven by climate variability and calving processes, to which the influence of enhanced thinning at ice cliff location can be added.

全球范围内针对有碎屑覆盖的冰川（debris-covered glaciers）的大量冰川学观测均表明，相较于气候变率，此类冰川的长度与物质平衡调整存在滞后效应，这一现象通常被归因于厚碎屑层对冰体的隔热效应。然而，有碎屑覆盖冰川的碎屑覆盖层、冰川几何形态与表面地形之间的动力相互作用，仍可随时间调控冰川流速与物质变化，诸多冰川即便被厚碎屑层覆盖，仍表现出较高的消融减薄速率。此类动力相互作用正逐步被纳入冰川演化研究领域。本文基于卫星影像、航空影像与数字高程模型（Digital Elevation Models），重建了1958年至2020年间巴塔哥尼亚安第斯山脉内3条有碎屑覆盖冰川的碎屑覆盖面积、表面流速及表面特征的变化过程。研究结果显示，自1958年起，碎屑覆盖面积占冰川总面积的比例已从40±0.6%提升至50±6.7%，同时冰川坡度略有降低。过去二十年间，平缓倾斜的冰舌使得表面流速维持在相对较低的水平（<60 m·a⁻¹），阻碍了表面碎屑的迁移，并推动了冰崖区域上边界的形成与抬升。此外，对过去二十年夏末雪线海拔的测绘结果表明，平衡线海拔（Equilibrium Line Altitudes）有所上升，这会促使冰内碎屑更早完成消融出露，并进一步扩大有碎屑覆盖的冰体面积。本次研究涉及的3条冰川在整个观测期内均呈现强烈负物质平衡，加之碎屑覆盖范围与上游冰崖区域的扩张，以及较低的表面流速，表明碎屑覆盖、物质平衡演化、表面流速与地形之间存在显著关联。值得注意的是，冰川最下游区域的厚碎屑层并未降低这些冰体区域的减薄速率，这表明物质平衡主要由气候变率与冰川崩解过程主导，而冰崖区域的增强减薄也可对其产生额外影响。