Sub-surface processes and heat fluxes at coarse-blocky Murtèl rock glacier (Engadine, eastern Swiss Alps)

IF 2.8 2区 地球科学 Q2 GEOGRAPHY, PHYSICAL Earth Surface Dynamics Pub Date : 2024-03-25 DOI:10.5194/egusphere-2024-172
Dominik Amschwand, Jonas Wicky, Martin Scherler, Martin Hoelzle, Bernhard Krummenacher, Anna Haberkorn, Christian Kienholz, Hansueli Gubler
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Abstract

Abstract. We estimate the sub-surface energy budget and heat fluxes in the coarse-blocky active layer (AL) of the Murtèl rock glacier, a seasonally snow-covered permafrost landform located in the eastern Swiss Alps. In the highly permeable AL, conductive/diffusive heat transfer including thermal radiation, non-conductive heat transfer by air circulation (convection), and heat storage changes from seasonal accretion and melting of ground ice shape the ground thermal regime. We quantify individual heat fluxes based on a novel in-situ sensor array in the AL and direct observations of the ground ice melt in the years 2020–2022. Two thaw-season mechanisms render Murtèl rock glacier comparatively climate-resilient. First, the AL intercepts ~70 % (55–85 MJ m−2) of the thaw-season ground heat flux by melting ground ice that runs off as meltwater, ~20 % (10–20 MJ m2) is spent on heating the blocks, and only ~10 % (7–13 MJ m2) is transferred into the permafrost body beneath and causes slow permafrost degradation. Second, the effective thermal conductivity in the ventilated AL increases from 1.2 W m1 K1 under strongly stable temperature gradients to episodically over 10 W m1 K1 under unstable temperature gradients, favouring convective cooling by buoyancy-driven Rayleigh ventilation (thermal semiconductor effect). In winter, radiatively cooled air infiltrating through a discontinuous, semi-closed snowcover leads to strong AL cooling. The two characteristic parameters (effective thermal conductivity and intrinsic permeability) are sensitive to debris texture, hence these convective undercooling processes are specific to highly permeable coarse-blocky material.
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粗块状穆尔泰尔岩石冰川(瑞士阿尔卑斯山东部恩加丁地区)的地表下过程和热通量
摘要我们估算了位于瑞士阿尔卑斯山东部的穆尔泰尔岩石冰川(一种季节性积雪覆盖的永久冻土地貌)粗块状活动层(AL)的次表层能量预算和热通量。在高渗透性的活动层中,包括热辐射在内的传导性/扩散性热传递、空气循环(对流)产生的非传导性热传递以及地冰季节性增厚和融化产生的热储量变化决定了地热状态。我们根据 AL 中的新型原位传感器阵列和 2020-2022 年对地冰融化的直接观测,对各个热通量进行了量化。两种解冻季节机制使穆尔泰勒岩石冰川具有相对较强的气候适应能力。首先,融化季的地面热通量中,约 70% (55-85 兆焦耳/平方米-2)由融化的地冰截取,以融水形式流走,约 20% (10-20 兆焦耳/平方米-2)用于加热块体,只有约 10% (7-13 兆焦耳/平方米-2)转移到下面的永久冻土体中,导致永久冻土缓慢降解。其次,在温度梯度非常稳定的情况下,通风冻土层的有效热传导率从 1.2 W m-1 K-1 增加到温度梯度不稳定时的 10 W m-1 K-1 以上,有利于通过浮力驱动的雷利通风进行对流冷却(热半导体效应)。在冬季,辐射冷却空气通过不连续的半封闭雪盖渗入,导致强烈的 AL 冷却。这两个特征参数(有效热导率和固有渗透率)对碎屑质地非常敏感,因此这些对流过冷过程是高渗透性粗块状物质所特有的。
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来源期刊
Earth Surface Dynamics
Earth Surface Dynamics GEOGRAPHY, PHYSICALGEOSCIENCES, MULTIDISCI-GEOSCIENCES, MULTIDISCIPLINARY
CiteScore
5.40
自引率
5.90%
发文量
56
审稿时长
20 weeks
期刊介绍: Earth Surface Dynamics (ESurf) is an international scientific journal dedicated to the publication and discussion of high-quality research on the physical, chemical, and biological processes shaping Earth''s surface and their interactions on all scales.
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