skip to main content

Search for: All records

Creators/Authors contains: "Bergstedt, Helena"

Note: When clicking on a Digital Object Identifier (DOI) number, you will be taken to an external site maintained by the publisher. Some full text articles may not yet be available without a charge during the embargo (administrative interval).
What is a DOI Number?

Some links on this page may take you to non-federal websites. Their policies may differ from this site.

  1. Environmental impact assessments for new Arctic infrastructure do not adequately consider the likely long-term cumulative effects of climate change and infrastructure to landforms and vegetation in areas with ice-rich permafrost, due in part to lack of long-term environmental studies that monitor changes after the infrastructure is built. This case study examines long-term (1949–2020) climate- and road-related changes in a network of ice-wedge polygons, Prudhoe Bay Oilfield, Alaska. We studied four trajectories of change along a heavily traveled road and a relatively remote site. During 20 years prior to the oilfield development, the climate and landscapes changed very little. During 50 years after development, climate-related changes included increased numbers of thermokarst ponds, changes to ice-wedge-polygon morphology, snow distribution, thaw depths, dominant vegetation types, and shrub abundance. Road dust strongly affected plant-community structure and composition, particularly small forbs, mosses, and lichens. Flooding increased permafrost degradation, polygon center-trough elevation contrasts, and vegetation productivity. It was not possible to isolate infrastructure impacts from climate impacts, but the combined datasets provide unique insights into the rate and extent of ecological disturbances associated with infrastructure-affected landscapes under decades of climate warming. We conclude with recommendations for future cumulative impact assessments in areas with ice-rich permafrost.
  2. We studied processes of ice-wedge degradation and stabilization at three sites adjacent to road infrastructure in the Prudhoe Bay Oilfield, Alaska, USA. We examined climatic, environmental, and subsurface conditions and evaluated vulnerability of ice wedges to thermokarst in undisturbed and road-affected areas. Vulnerability of ice wedges strongly depends on the structure and thickness of soil layers above ice wedges, including the active, transient, and intermediate layers. In comparison with the undisturbed area, sites adjacent to the roads had smaller average thicknesses of the protective intermediate layer (4 cm vs. 9 cm), and this layer was absent above almost 60% of ice wedges (vs. ∼45% in undisturbed areas). Despite the strong influence of infrastructure, ice-wedge degradation is a reversible process. Deepening of troughs during ice-wedge degradation leads to a substantial increase in mean annual ground temperatures but not in thaw depths. Thus, stabilization of ice wedges in the areas of cold continuous permafrost can occur despite accumulation of snow and water in the troughs. Although thermokarst is usually more severe in flooded areas, higher plant productivity, more litter, and mineral material (including road dust) accumulating in the troughs contribute to formation of the intermediate layer, which protects ice wedges from further melting.
  3. Abstract. Thermokarst lake dynamics, which play an essential role in carbon releasedue to permafrost thaw, are affected by various geomorphological processes.In this study, we derive a three-dimensional (3D) Stefan equation tocharacterize talik geometry under a hypothetical thermokarst lake in thecontinuous permafrost region. Using the Euler equation in the calculus ofvariations, the lower bounds of the talik were determined as an extremum ofthe functional describing the phase boundary area with a fixed total talikvolume. We demonstrate that the semi-ellipsoid geometry of the talik isoptimal for minimizing the total permafrost thaw under the lake for a givenannual heat supply. The model predicting ellipsoidal talik geometry wascompared to talik thickness observations using transient electromagnetic(TEM) soundings in Peatball Lake on the Arctic Coastal Plain (ACP) ofnorthern Alaska. The depth : width ratio of the elliptical sub-lake talik cancharacterize the energy flux anisotropy in the permafrost, although the lakebathymetry cross section may not be elliptic due to the presence ofnear-surface ice-rich permafrost. This theory suggests that talikdevelopment deepens lakes and results in more uniform horizontal lakeexpansion around the perimeter of the lakes, while wind-induced waves andcurrents are likely responsible for the elongation and orientation ofshallow thermokarst lakes without taliks in certain regions such as the ACPof northernmore »Alaska.« less
  4. Abstract
    This data set covers the younger outer coastal plain north of Teshekpuk Lake, North Slope, Alaska. In this region, drained lake basins are abundant features, covering large parts of the landscape. This data set is based on Landsat Thematic Mapper (TM) imagery acquired in August 2010, and a 5 meter (m) resolution Interferometric Synthetic Aperture Radar (IfSAR)-derived digital terrain model. Drained lake basins were manually delineated in a geographic information system (GIS). The data set includes Lake 195, which drained in this area in 2014. For further details please see Jones et al. (2015): Jones, BM, and Arp, CD (2015), Observing a Catastrophic Thermokarst Lake Drainage in Northern Alaska. Permafrost and Periglac. Process., 26, 119– 128. doi: 10.1002/ppp.1842.
  5. null (Ed.)
    Lake formation and drainage are pervasive phenomena in permafrost regions. Drained lake basins (DLBs) are often the most common landforms in lowland permafrost regions in the Arctic (50% to 75% of the landscape). However, detailed assessments of DLB distribution and abundance are limited. In this study, we present a novel and scalable remote sensing-based approach to identifying DLBs in lowland permafrost regions, using the North Slope of Alaska as a case study. We validated this first North Slope-wide DLB data product against several previously published sub-regional scale datasets and manually classified points. The study area covered >71,000 km2, including a >39,000 km2 area not previously covered in existing DLB datasets. Our approach used Landsat-8 multispectral imagery and ArcticDEM data to derive a pixel-by-pixel statistical assessment of likelihood of DLB occurrence in sub-regions with different permafrost and periglacial landscape conditions, as well as to quantify aerial coverage of DLBs on the North Slope of Alaska. The results were consistent with previously published regional DLB datasets (up to 87% agreement) and showed high agreement with manually classified random points (64.4–95.5% for DLB and 83.2–95.4% for non-DLB areas). Validation of the remote sensing-based statistical approach on the North Slope of Alaska indicated thatmore »it may be possible to extend this methodology to conduct a comprehensive assessment of DLBs in pan-Arctic lowland permafrost regions. Better resolution of the spatial distribution of DLBs in lowland permafrost regions is important for quantitative studies on landscape diversity, wildlife habitat, permafrost, hydrology, geotechnical conditions, and high-latitude carbon cycling.« less
  6. Abstract
    This data set covers the Anaktuvuk River fire site and maps drained lake basins in this area as described by Jones et al (2015). The data set is derived from airborne Light Detection and Ranging (LiDAR) data acquired in 2009 and 2014. The classification of drained lake basins is based on digital terrain models (DTMs) created from the classified LiDAR data and using the a topographic position index (TPI). The TPI output was manually categorized relative to existing surficial geology maps and refined into the following terrain units: (1) drained lake basins, (2) yedoma uplands, (3) rocky uplands, (4) glaciated upland, (5) river floodplain and (6) tundra stream gulches. The drained lake basin class is the subject of this data set publication. Jones, B., Grosse, G., Arp, C. et al. Recent Arctic tundra fire initiates widespread thermokarst development. Sci Rep 5, 15865 (2015).
  7. Abstract
    This data set contains a classification of the North Slope, Alaska for drained lake basins (DLBs) based on Landsat-8 imagery of the years 2014-2019 and Arctic Digital Elevation Model (ArcticDEM) data. Drained lake basins (DLBs) are often the most common landforms in lowland permafrost regions in the Arctic (50% to 75% of the landscape). However, detailed assessments of DLB distribution and abundance are limited. This data set is based on a novel and scalable remote sensing-based approach to identify DLBs in lowland permafrost regions, using the North Slope of Alaska as a case study. The data set was validated against several prior sub-regional scale datasets and manually classified points. The study area covers greater than 71,000 square kilometers (km2), including a greater than 39,000 km2 area not previously covered in existing DLB data sets. Within the data set, three classes are present: DLB/ambiguous/noDLB. Areas classified as ambiguous could not be classified as DLB or noDLB with sufficient certainty. Users may decide on a case by case basis if they wish to use the conservative estimate of DLB area, therefore omitting areas classified as ambiguous, or to use all three classes.