Mapping geothermal heat flux using permafrost thickness constrained by airborne electromagnetic surveys on the western coast of Ross Island, Antarctica
Mapping geothermal heat flux using permafrost thickness constrained by airborne electromagnetic surveys on the western coast of Ross Island, Antarctica
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DOI：
10.1080/08123985.2019.1651618
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发表时间：
2020-01
影响因子：
0.9
通讯作者：
N. Foley;S. Tulaczyk;E. Auken;D. Grombacher;J. Mikucki;N. Foged;K. Myers;H. Dugan;P. Doran;R. Virginia
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文献类型：
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作者：
N. Foley;S. Tulaczyk;E. Auken;D. Grombacher;J. Mikucki;N. Foged;K. Myers;H. Dugan;P. Doran;R. Virginia
摘要多年冻土在高纬度地区普遍存在，其厚度受地热通量、地表温度和地下热物性等重要局部因素的控制。我们使用航空瞬变电磁电阻率测量，以确定永久冻土厚度的罗斯岛，南极洲，其中包含的活火山山埃里伯斯海岸。在这里，电阻率数据清楚地将电阻性永久冻土与其下的导电流体饱和材料区分开来。在我们的研究中，我们将永久冻土定义为电阻率> 100 Ω·m的冻结材料;导电性更高的材料含有大量的水或（更可能）盐水。我们观察到，永久冻土层在海岸附近非常薄，在内陆几百米内变厚，深度通常在300-400米之间。我们认为，近海岸冻土厚度的急剧增加，从相对温暖的海洋横向热传导，可能与海水渗透到近海岸冻土。我们用二维热流模型验证了这一结果，并得出结论，远离海洋的热影响，当地的地热梯度和热通量分别约为45 ± 5 °C/km和90 ± 13 mW/m2。这些数值与公布的埃里伯斯山附近和正在积极延伸的恐怖裂谷内的估计值一致，但并不反映埃里伯斯山火山活动产生的强烈热流异常。以前在麦克默多湾另一边的麦克默多干谷进行的测量往往要低几十毫瓦/平方米，这可能反映了跨南极山脉隆起裂谷肩部的不同构造环境。我们的研究展示了一种新的方法来约束地热通量在极地地区使用航空电磁（AEM）数据，可以相对有效地收集在区域尺度上的冰覆盖不超过AEM设备的渗透限制，这对于所使用的设备是500米的有利条件下，在研究区域。
ABSTRACT Permafrost is ubiquitous at high latitudes, and its thickness is controlled by important local factors like geothermal flux, ground surface temperature and thermal properties of the subsurface. We use airborne transient electromagnetic resistivity measurements to determine permafrost thickness on the coast of Ross Island, Antarctica, which contains the active volcano Mt Erebus. Here, resistivity data clearly distinguish resistive permafrost from the electrically conductive fluid-saturated materials underlying it. For our study, we define permafrost as frozen material with a resistivity > 100 Ω·m; more conductive material contains a significant fraction of water or (more likely) brine. We observe that permafrost is very thin near the coast and thickens within several hundred metres inland to reach depths that are typically within the range of 300–400 m. We attribute the sharp near-shore increase in permafrost thickness to lateral heat conduction from the relatively warm ocean, possibly combined with seawater infiltration into the near-shore permafrost. We validate this result with a two-dimensional heat flow model and conclude that away from the thermal influence of the ocean, the local geothermal gradient and heat flux are about 45 ± 5 °C/km and 90 ± 13 mW/m2, respectively. These values are in line with published estimates in the vicinity of Mt Erebus and within the actively extending Terror Rift, but do not reflect a strong heat flow anomaly from volcanic activity of Mt Erebus. Measurements made previously in the McMurdo Dry Valleys, on the other side of McMurdo Sound, tend to be a few dozens of mW/m2 lower, likely reflecting its different tectonic setting on the uplifted rift shoulder of Transantarctic Mountains. Our study demonstrates a new approach towards constraining geothermal flux in polar regions using airborne electromagnetic (AEM) data that can be relatively efficiently collected on regional scales where ice coverage does not exceed the penetration limits of the AEM device, which for the device used is ∼ 500 m under the favourable conditions in the study area.