| 1. |
- Westermann, Sebastian, et al.
(författare)
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The CryoGrid community model (version 1.0) - a multi-physics toolbox for climate-driven simulations in the terrestrial cryosphere
- 2023
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Ingår i: Geoscientific Model Development. - 1991-959X .- 1991-9603. ; 16, s. 2607-2647
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Tidskriftsartikel (refereegranskat)abstract
- The CryoGrid community model is a flexible toolbox for simulating the ground thermal regime and the ice-water balance for permafrost and glaciers, extending a well-established suite of permafrost models (CryoGrid 1, 2, and 3). The CryoGrid community model can accommodate a wide variety of application scenarios, which is achieved by fully modular structures through object-oriented programming. Different model components, characterized by their process representations and parameterizations, are realized as classes (i.e., objects) in CryoGrid. Standardized communication protocols between these classes ensure that they can be stacked vertically. For example, the CryoGrid community model features several classes with different complexity for the seasonal snow cover, which can be flexibly combined with a range of classes representing subsurface materials, each with their own set of process representations (e.g., soil with and without water balance, glacier ice). We present the CryoGrid architecture as well as the model physics and defining equations for the different model classes, focusing on one-dimensional model configurations which can also interact with external heat and water reservoirs. We illustrate the wide variety of simulation capabilities for a site on Svalbard, with point-scale permafrost simulations using, e.g., different soil freezing characteristics, drainage regimes, and snow representations, as well as simulations for glacier mass balance and a shallow water body. The CryoGrid community model is not intended as a static model framework but aims to provide developers with a flexible platform for efficient model development. In this study, we document both basic and advanced model functionalities to provide a baseline for the future development of novel cryosphere models.
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| 2. |
- Anderson, N. John, et al.
(författare)
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The Arctic in the Twenty-First Century : Changing Biogeochemical Linkages across a Paraglacial Landscape of Greenland
- 2017
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Ingår i: BioScience. - : Oxford University Press. - 0006-3568 .- 1525-3244. ; 67:2, s. 118-133
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Tidskriftsartikel (refereegranskat)abstract
- The Kangerlussuaq area of southwest Greenland encompasses diverse ecological, geomorphic, and climate gradients that function over a range of spatial and temporal scales. Ecosystems range from the microbial communities on the ice sheet and moisture-stressed terrestrial vegetation (and their associated herbivores) to freshwater and oligosaline lakes. These ecosystems are linked by a dynamic glacio-fluvial-aeolian geomorphic system that transports water, geological material, organic carbon and nutrients from the glacier surface to adjacent terrestrial and aquatic systems. This paraglacial system is now subject to substantial change because of rapid regional warming since 2000. Here, we describe changes in the eco-and geomorphic systems at a range of timescales and explore rapid future change in the links that integrate these systems. We highlight the importance of cross-system subsidies at the landscape scale and, importantly, how these might change in the near future as the Arctic is expected to continue to warm.
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| 3. |
- Biskaborn, Boris K., et al.
(författare)
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Permafrost is warming at a global scale
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Permafrost warming has the potential to amplify global climate change, because when frozen sediments thaw it unlocks soil organic carbon. Yet to date, no globally consistent assessment of permafrost temperature change has been compiled. Here we use a global data set of permafrost temperature time series from the Global Terrestrial Network for Permafrost to evaluate temperature change across permafrost regions for the period since the International Polar Year (2007–2009). During the reference decade between 2007 and 2016, ground temperature near the depth of zero annual amplitude in the continuous permafrost zone increased by 0.39 ± 0.15 °C. Over the same period, discontinuous permafrost warmed by 0.20 ± 0.10 °C. Permafrost in mountains warmed by 0.19 ± 0.05 °C and in Antarctica by 0.37 ± 0.10 °C. Globally, permafrost temperature increased by 0.29 ± 0.12 °C. The observed trend follows the Arctic amplification of air temperature increase in the Northern Hemisphere. In the discontinuous zone, however, ground warming occurred due to increased snow thickness while air temperature remained statistically unchanged.
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| 4. |
- Ingeman-Nielsen, Thomas, et al.
(författare)
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Effect of electrode shape on grounding resistances — Part 1: The focus-one protocol
- 2016
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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 81:1, s. 159-167
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Tidskriftsartikel (refereegranskat)abstract
- Electrode grounding resistance is a major factor affecting measurement quality in electric resistivity tomography (ERT) measurements for cryospheric applications. Still, little information is available on grounding resistances in the geophysical literature, mainly because it is difficult to measure. The focus-one protocol is a new method for estimating single electrode grounding resistances by measuring the resistance between a single electrode in an ERT array and all the remaining electrodes connected in parallel. For large arrays, the measured resistance is dominated by the grounding resistance of the electrode under test, the focus electrode. We have developed an equivalent circuit model formulation for the resistance measured when applying the focus-one protocol. Our model depends on the individual grounding resistances of the electrodes of the array, the mutual resistances between electrodes, and the instrument input impedance. Using analytical formulations for the potentials around prolate and oblate spheroidal electrode models (as approximations for rod and plate electrodes), we have investigated the performance and accuracy of the focus-one protocol in estimating single-electrode grounding resistances. We also found that the focus-one protocol provided accurate estimations of electrode grounding resistances to within 7% for arrays of 30 electrodes or more when the ratio of instrument input impedance to the half-space resistivity was 1000 m−1 or more. The focus-one protocol was of high practical value in field operations because it helped to optimize array installation, electrode design, and placement. The measured grounding resistances may also be included in future inversion schemes to improve data interpretation under difficult environmental conditions such as those encountered in cryospheric applications.
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| 5. |
- Tomaškovičová, Soňa, et al.
(författare)
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Effect of electrode shape on grounding resistances — Part 2: Experimental results and cryospheric monitoring
- 2016
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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 81:1, s. 169-182
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Tidskriftsartikel (refereegranskat)abstract
- Although electric resistivity tomography (ERT) is now regarded as a standard tool in permafrost monitoring, high grounding resistances continue to limit the acquisition of time series over complete freeze-thaw cycles. In an attempt to alleviate the grounding resistance problem, we have tested three electrode designs featuring increasing sizes and surface area, in the laboratory and at three different field sites in Greenland. Grounding resistance measurements showed that changing the electrode shape (using plates instead of rods) reduced the grounding resistances at all sites by 28%–69% during unfrozen and frozen ground conditions. Using meshes instead of plates (the same rectangular shape and a larger effective surface area) further improved the grounding resistances by 29%–37% in winter. Replacement of rod electrodes of one entire permanent permafrost monitoring array by meshes resulted in an immediate reduction of the average grounding resistance by 73% from 1.5 to 0.4 kΩ (unfrozen conditions); in addition, the length of the acquisition period during the winter season was markedly prolonged. Grounding resistance time series from the three ERT monitoring stations in Greenland showed that the electrodes were rarely perfectly grounded and that grounding resistances exceeding 1 MΩ may occur in severe cases. We concluded that the temperature, electrode shape, and lithology at the sites have a marked impact on electrode performance. Choosing an optimized electrode design may be the deciding factor for successful data acquisition, and should therefore be considered when planning a long-term monitoring project.
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| 6. |
- Zastruzny, Sebastian F., et al.
(författare)
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Accelerated permafrost thaw and increased drainage in the active layer : Responses from experimental surface alteration
- 2023
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Ingår i: Cold Regions Science and Technology. - 0165-232X. ; 212
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Tidskriftsartikel (refereegranskat)abstract
- Erosion and infrastructure in the Arctic can change the thickness of the active layer which can subsequently alternate the thermal-hydrological regime and change the drainage patterns on slopes. Previous studies have shown that drainage can either decrease due to the movement of water occurring in deeper soil layers with lower permeability or increase due to the formation of features like gullies and channels. In a field experiment conducted in Qaanaaq, Greenland, the surface topography was altered by adding 35 cm soil in one treatment, removing 33 cm in another, while an untreated plot measuring 10 × 10 m was maintained for comparison purposes. The temperature and water content of these plots were monitored in the three following years. Based on field measurements, a 1-dimensional model was set up in CoupModel to simulate the field experiment and quantify changes in the thickness of the saturated zone and drainage as a consequence of the treatment. Both field observations and simulations show that the addition and removal of soil changed the thickness of the saturated layer in the active layer, which changed the thermal properties in the soil and, thus, the response of thawing or recovery of permafrost. The simulations showed that during the summer depressions there were higher water contents, which accelerated warming of the soil and increased permafrost thawing of 35.7 cm in depth. In contrast, raising the soil surface aggregated only 19.8 cm of permafrost due to higher buffering from lower water contents. Changed active layer thickness altered the thickness of the saturated zone, leading to changed drainage patterns: In depressions, first drainage occurs three days earlier, and maximum daily drainage is increased by 154% as compared to ambient conditions. In contrast, raising the surface delayed the runoff from the plot by up to eight days, and decreased the maximum daily drainage to 72%. Effects of the treatment were most pronounced during the first year after the experiment, with diminishing effects during the consecutive year as the system equilibrated to the new state. Results from our study can advance our understanding of impacts of both natural and human-induced surface alterations on active layer thickening and water movement in permafrost-affected areas, which ultimately affect the entire ecosystem and the living conditions for local communities.
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