| 1. |
- Ehnvall, B., et al.
(author)
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Topography and time shape mire morphometry and large-scale mire distribution patterns in the northern boreal landscape
- 2024
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In: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 129:2
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Journal article (peer-reviewed)abstract
- Peatlands are major terrestrial soil carbon stores, and open mires in boreal landscapes hold a considerable fraction of the global peat carbon. Despite decades of study, large-scale spatiotemporal analyses of mire arrangement have been scarce, which has limited our ability to scale-up mire properties, such as carbon accumulation to the landscape level. Here, we use a land-uplift mire chronosequence in northern Sweden spanning 9,000 years to quantify controls on mire distribution patterns. Our objectives include assessing changes in the spatial arrangement of mires with land surface age, and understanding modifications by upland hydrotopography. Characterizing over 3,000 mires along a 30 km transect, we found that the time since land emergence from the sea was the dominant control over mire coverage, especially for the establishment of large mire complexes. Mires at the youngest end of the chronosequence were small with heterogenous morphometry (shape, slope, and catchment-to-mire areal ratios), while mires on the oldest surfaces were variable in size, but included larger mires with more complex shapes and smaller catchment-to-mire ratios. In general, complex topography fragmented mires by constraining the lateral expansion, resulting in a greater number of mires, but reduced total mire area regardless of landscape age. Mires in this study area occurred on slopes up to 4%, indicating a hydrological boundary to peatland expansion under local climatic conditions. The consistency in mire responses to spatiotemporal controls illustrates how temporal limitation in peat initiation and accumulation, and topographic constraints to mire expansion together have shaped present day mire distribution patterns.
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| 2. |
- Hofstede, C., et al.
(author)
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The Subglacial Lake That Wasn't There : Improved Interpretation From Seismic Data Reveals a Sediment Bedform at Isunnguata Sermia
- 2023
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In: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 128:10
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Journal article (peer-reviewed)abstract
- Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km(2) flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co-located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens-shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 +/- 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water-bearing sediments with R = -0.10 +/- 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water-storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens-shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate. Plain Language Summary A ground based radar survey in West Greenland showed an unusually flat, highly reflective zone in an otherwise rough bed suggesting a possible subglacial lake beneath the ice. The highly reflective zone was part of a drainage system transporting meltwater under the ice sheet. We performed a detailed seismic survey across the area which, unlike radar signals, has the advantage of penetrating through the overlying ice into any rock, sediments and water below it. Analysis of our reflection data reveal that the flat area was in fact an elongated lens-shaped bedform consisting of layered (stratified) sediments. However at a larger angle of incidence, analysis showed the bedform is possibly overlain by a thin layer of water-bearing sediments likely saturated by ponding water. Our interpretation is that episodically draining meltwater from upstream is locally accumulating beneath the ice sheet at this locality, thereby depositing the lens-shaped bedform over many melt seasons.
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| 3. |
- Holmes, Felicity A., et al.
(author)
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Calving at Ryder Glacier, Northern Greenland
- 2021
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In: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 126:4
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Journal article (peer-reviewed)abstract
- Recent evidence has shown increasing mass loss from the Greenland ice sheet, with a general trend of accelerated mass losses extending northwards. However, different glaciers have been shown to respond differently to similar external forcings, constituting a problem for extrapolating and upscaling data. Specifically, whilst some outlet glaciers have accelerated, thinned, and retreated in response to atmospheric and oceanic warming, the behavior of other marine terminating glaciers appears to be less sensitive to climate forcing. Ryder glacier, for which only a few studies have been conducted, is located in North Greenland and terminates with a floating ice tongue in Sherard Osborn Fjord. The persistence or disintegration of floating ice tongues has impacts on glacier dynamics and stability, with ramifications beyond, including sea level rise. This study focuses on understanding the controls on calving and frontal ablation of the Ryder glacier through the use of time-lapse imagery and satellite data. The results suggest that Ryder glacier has behaved independently of climate forcing during recent decades, with fjord geometry exerting a first order control on its calving.
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| 4. |
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| 5. |
- Mason, Richard J., et al.
(author)
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Aquatic Insect Bioconstructions Modify Fine-Sediment Entrainment and Mobility
- 2022
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In: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 127:2
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Journal article (peer-reviewed)abstract
- The importance of two-way interactions between animals and the physical hydraulic and sedimentological environment are increasingly recognized (e.g., zoogeomorphology). Caddisflies (Trichoptera) are a group of aquatic insects known for their bioconstructions, particularly cases built from fine sediment and silk. Caddisfly cases differ in size, shape and density from the incorporated sediment, and case construction may therefore affect the mobility of these sediments in rivers. However, although communities of caddisfly often use substantial quantities of sediment in case construction, the effect of these bioconstructions on sediment transport in rivers is unknown. We use a flume experiment to compare the bed shear stress required to transport (a) empty caddisfly cases and (b) individual sediment particles, following disaggregation from the case. The cases of three species were considered; two that construct different styles of tubular case (Potamophlax latipennis and Sericostoma personatum) and one that builds a domed case (Agapetus fuscipes). P. latipennis and S. personatum cases were easier to entrain than the sediment grains incorporated into them, whilst A. fuscipes cases were not. Despite their low mass, A. fuscipes cases required the most shear stress to transport them because their domed shape impeded rolling. These findings are important to understand how differences in case design between species, reflect different adaptation strategies to the turbulent hydraulic river habitat. Furthermore, the results suggest that un-attached tubular caddisfly cases may be preferentially transported over other particles on the river bed and thus, where caddisfly occur in high abundance, they may increase fluvial entrainment of sand.
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| 6. |
- Oestreicher, Nicolas, et al.
(author)
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Bedrock Fractures Control Groundwater-Driven Mountain Slope Deformations
- 2023
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In: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 128:11
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Journal article (peer-reviewed)abstract
- Seasonal deformation of mountain rock slopes can be driven by groundwater infiltration and depletion. Such processes could explain our field observation in the Aletsch Valley, Switzerland, where GNSS-derived 3D annual displacement amplitudes reach 3.4 cm. However, the physical mechanisms behind such groundwater-driven surface displacements are not well understood. Here, we develop a fully coupled hydromechanical model to simulate the relevant processes in a valley slope embedded with numerous fractures of variable sizes. The magnitude and orientation of transient annual slope surface displacement obtained from our model are in overall agreement with the field observations. The key geological factors controlling the type and magnitude of reversible mountain slope deformations are fracture network geometry, fracture aperture, and regional stress field. We show that the heterogeneity and anisotropy of bedrock hydromechanical responses, originating from depth-dependent variations of fracture properties, play a critical role in groundwater recharge and valley slope deformation. During recharge events, pore pressure perturbations migrate downward from the groundwater table and toward the receiving stream and the deep subsurface. This process driven by pressure diffusion and poroelastic stressing develops in the subsurface with a great reach of up to a few kilometers, called critical hydromechanical response zone, and controls surface deformation patterns. During groundwater recession, this hydromechanical response zone expands downward and ground surface displacement vectors rotate upwards. Our results suggest that slope surface deformation can inform about subsurface permeability structures and pore pressure fluctuations, which have important implications for understanding groundwater flow in fractured bedrock slopes.
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| 7. |
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| 8. |
- Polvi, Lina E., et al.
(author)
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Seismic Monitoring of a Subarctic River : Seasonal Variations in Hydraulics, Sediment Transport, and Ice Dynamics
- 2020
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In: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 125:7
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Journal article (peer-reviewed)abstract
- High-latitude rivers are commonly covered by ice for up to one third of the year. Our understanding of the effects of ice on channel morphodynamics and bedload transport is hindered by the difficulties of sensing through the ice and dangers of field work on thin ice or during ice break-up. To avoid this drawback, we used seismic signals to interpret processes and quantify water and sediment fluxes. Our objective was to determine seasonal differences in hydraulics and bedload sediment transport under ice-covered versus open-channel flow conditions using a small seismic network and to provide a first-order estimation of sediment flux in a Fennoscandian river. Our study reach was on a straight, low-gradient section of the Savar River in northern Sweden. Interpretations of seismic signals, from a station 40 m away from the river, and inverted physical models of river stage and bedload flux indicate clear seasonal differences between ice-covered and open-channel flow conditions. Diurnal cycles in seismic signals reflecting turbulence and sediment transport are evident directly after ice break-up. Analysis of seismic signals of ice-cracking support our visual interpretation of ice break-up timing and the main ice break-up mechanism as thermal rather than mechanical. Assuming the bulk of sediment moves during ice break-up and the snowmelt flood, we calculate a minimum annual sediment flux of 56.2 +/- 0.7 t/km(2), which drastically reduces the uncertainty from previous estimates (0-50 t/km(2)) that exclude ice-covered or ice break-up periods.
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| 9. |
- Schaffer, Nicole, et al.
(author)
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Revised estimates of recent mass loss rates for Penny Ice Cap, Baffin Island, based on 2005-2014 elevation changes modified for firn densification
- 2020
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In: Journal of Geophysical Research - Earth Surface. - : American Geophysical Union (AGU). - 2169-9003 .- 2169-9011. ; 125:8
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Journal article (peer-reviewed)abstract
- Repeat airborne or satellite measurements of surface elevation over ice caps are often used tocalculate glacier‐wide surface mass changes over time. However, these measurements typically do notaccount for vertical ice motion caused by firn densification and/or ice flow, so the effect of these factors formass change measurements over an entire ice cap are currently poorly constrained. In this study, we updateNASA Airborne Topographic Mapper (ATM) altimetry elevation changes across Penny Ice Cap (BaffinIsland, Canada) to assess total changes in ice mass from 2005–2014, relative to 1995–2000. Dual‐frequencyGPS measurements and temporal changes in ice core density profiles are used to calculate firn densificationand ice flow to isolate the component of elevation change due to surface mass change. Envisat satelliteimagery is used to delineate the areas impacted by firn densification. These calculations, the first for aCanadian Arctic ice cap, indicate that accounting for firn densification may reduce the inferred surface massloss by ~13–15%. Overall, there has been a fourfold increase in mass loss from Penny Ice Cap between1995–2000 (−1.3 ± 0.7 Gt a−1) and 2005–2013 (−5.4 ± 1.9 Gt a−1). The rapid upglacier migration of theequilibrium line has left large areas of subsurface firn in the current ablation area and has far outpaced theice flow response, illustrating that the ice cap is not in equilibrium and out of balance with the currentclimate.
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| 10. |
- Woodard, J. B., et al.
(author)
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Variations in Hard-Bedded Topography Beneath Glaciers
- 2021
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In: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 126:9
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Journal article (peer-reviewed)abstract
- The morphology of glacier beds is a first-order control on their slip speeds and consequent rates of subglacial erosion. As such, constraining the range of bed shapes expected beneath glaciers will improve estimates of glacier slip speeds. To estimate the variability of subglacial bed morphology, we construct 10 high-resolution (10 cm) digital elevation models of proglacial areas near current glacier margins from point clouds produced through a combination of terrestrial laser scanning and photogrammetry techniques. The proglacial areas are located in the Swiss Alps and the Canadian Rockies and consist of predominantly debris-free bedrock of variable lithology (igneous, sedimentary, and metamorphic). We measure eight different spatial parameters intended to describe bed morphologies generated beneath glaciers. Using probability density functions, Bhattacharyya coefficients, principal component analysis, and Bayesian statistical models we investigate the significance of these spatial parameters. We find that the parameters span similar ranges, but the means and standard deviations of the parameter probability density functions are commonly distinct. These results indicate that glacier flow over bedrock may lead to a convergence toward a common bed morphology. However, distinct properties associated with each location prevent morphologies from being uniform.
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| 11. |
- Zheng, Xiaodi, et al.
(author)
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Extreme Copper Isotope Fractionation Driven by Redox Oscillation During Gleysols Weathering in Mun River Basin, Northeast Thailand
- 2023
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In: Journal of Geophysical Research - Earth Surface. - : John Wiley & Sons. - 2169-9003 .- 2169-9011. ; 128:3
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Journal article (peer-reviewed)abstract
- The fractionation of copper (Cu) isotope is a process related to the redox fluctuation during soil Cu biogeochemical cycling. For Cu isotope composition in weathered gleysols of tropical zones, the increased rates of redox fluctuations are assumed to occur during gleysol evolution due to the seasonal exchange of groundwater and river water. However, the impact of the frequency of redox fluctuations on soil Cu isotope signatures is rarely documented. Here, we analyzed the variations of Cu content and isotope fractionation in two low-humic gleysol profiles with different pedogenetic processes during weathering in the same basin (Mun River Basin), and found that the frequency of redox fluctuations could determine the magnitude of Cu isotope fractionation. We record an increased light Cu isotopes and identify the stable Cu(I) species retained in the residual soils with the increased frequency of redox fluctuation. Several processes contribute to Cu isotope fractionation at different soil horizons, but most isotope fractionation is related to the re-adsorption or re-precipitation by iron and manganese oxyhydroxide (i.e., ferrihydrite and pyrolusite), especially at the iron or manganese-rich zone. Cu isotope fractionation is sensitive to increased redox fluctuations in the terrestrial ecosystem, and may have significant implications for assessing soil ecological vulnerability under future climate change scenarios.
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| 12. |
- Åkesson, Henning, et al.
(author)
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Future Projections of Petermann Glacier Under Ocean Warming Depend Strongly on Friction Law
- 2021
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In: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 126:6
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Journal article (peer-reviewed)abstract
- Basal friction heavily controls the dynamics of fast-flowing glaciers. However, the best approach to modeling friction is unclear, increasing uncertainties in projections of future mass loss and sea-level rise. Here, we compare six friction laws and evaluate them for Petermann Glacier in northern Greenland, using a higher order three-dimensional ice-sheet model. We model glacier retreat and mass loss under an ocean-only warming until year 2300, while not considering the effects of a future warmer atmosphere. Regardless of the friction law, we find that breakup of Petermann's ice shelf is likely to occur within the next decades. However, future grounding-line retreat differs by 10s of km and estimates of sea-level rise may quadruple, depending on the friction law employed. A bedrock ridge halts the retreat for four of the laws, and Petermann retreats furthest when applying a Budd or a Coulomb-type till law. Depending on the friction law, sea-level contributions differ by 133% and 282% by 2300 for 2 degrees C and 5 degrees C ocean warming scenarios, respectively.
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| 13. |
- van IJzendoorn, C. O., et al.
(author)
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Modeling Multi-Fraction Coastal Aeolian Sediment Transport With Horizontal and Vertical Grain-Size Variability
- 2023
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In: Journal of Geophysical Research: Earth Surface. - 2169-9003. ; 128:7
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Journal article (peer-reviewed)abstract
- Grain size affects the rates of aeolian sediment transport on beaches. Sediment in coastal environments typically consists of multiple grain-size fractions and exhibits spatiotemporal variations. Still, conceptual and numerical aeolian transport models are simplified and often only include a single fraction that is constant over the model domain. It is unclear to what extent this simplification is valid and if the inclusion of multi-fraction transport and spatial grain-size variations affects aeolian sediment transport simulations and predictions of coastal dune development. This study applies the numerical aeolian sediment transport model AeoLiS to compare single-fraction to multi-fraction approaches for a range of grain-size distributions and spatial grain-size scenarios. The results show that on timescales of days to years, single-fraction simulations with the median grain size, D50, often give similar results to multi-fraction simulations, provided the wind is able to mobilize all fractions within that time frame. On these timescales, vertical variability in grain size has a limited effect on total transport rates, but it does influence the simulation results on minute timescales. Horizontal grain-size variability influences both the total transport rates and the downwind bed grain-size composition. The results provide new insights into the influence of beach sediment composition and spatial variability on total transport rates toward the dunes. The findings of this study can guide the implementation of grain-size variability in numerical aeolian sediment transport models.
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