Active Layer Sediment Research Articles

Permeability of active layer sediments and groundwater runoff in Brattegg River catchment, SW Spitsbergen

Permeability of active layer sediments and groundwater runoff in Brattegg River catchment, SW Spitsbergen

Detection of Ice Wedge Cracking in Permafrost Using Miniature Accelerometers

AbstractDetermining the exact timing of ice wedge cracking in permafrost is challenging. Five miniature accelerometers were installed near the ground surface in the trough of a primary ice wedge within a network of low‐centered polygons in Adventdalen, Svalbard, to test whether these instruments could be used to detect dynamics of thermal contraction cracking. Data from 2003 to 2013 were analyzed to characterize cryoseismic signals in the ice wedge trough. High‐magnitude accelerations (from 5 g to at least 100 g) were typically registered in late winter, when the top of permafrost had cooled to about −10°C; these likely correspond to ice wedge cracking in permafrost. Tensile stresses calculated from temperatures measured in the ice wedge trough are near laboratory strengths reported for ice and mineral active layer sediments, supporting the interpretation that large accelerations are caused by thermal contraction cracking. Lower magnitude accelerations occurred throughout the freezing season, usually coinciding with rapid cooling at the ground surface. These small accelerations may be associated with (i) the initiation of small cracks in the active layer of the trough or (ii) the horizontal and vertical propagation of existing ice wedge cracks. The results of this investigation indicate that miniature accelerometers are an effective, inexpensive, and simple method to determine the timing of ice wedge cracking and rates of crack propagation along ice wedge troughs.

Ill-posedness in modeling mixed sediment river morphodynamics

In this paper we analyze the Hirano active layer model used in mixed sediment river morphodynamics concerning its ill-posedness. Ill-posedness causes the solution to be unstable to short-wave perturbations. This implies that the solution presents spurious oscillations, the amplitude of which depends on the domain discretization. Ill-posedness not only produces physically unrealistic results but may also cause failure of numerical simulations. By considering a two-fraction sediment mixture we obtain analytical expressions for the mathematical characterization of the model. Using these we show that the ill-posed domain is larger than what was found in previous analyses, not only comprising cases of bed degradation into a substrate finer than the active layer but also in aggradational cases. Furthermore, by analyzing a three-fraction model we observe ill-posedness under conditions of bed degradation into a coarse substrate. We observe that oscillations in the numerical solution of ill-posed simulations grow until the model becomes well-posed, as the spurious mixing of the active layer sediment and substrate sediment acts as a regularization mechanism. Finally we conduct an eigenstructure analysis of a simplified vertically continuous model for mixed sediment for which we show that ill-posedness occurs in a wider range of conditions than the active layer model.

2D Modeling of Flow and Sediment Interaction: Sediment Mixtures

AbstractThe further development and application of the two-dimensional (2D) flow and sediment-modeling concept, formulated for the treatment of sediment mixtures, is addressed herein. The sediment domain is divided into subdomains for suspended, active-layer, and subsurface-strata sediments. Governing sediment equations are defined for each subdomain, including sediment exchange mechanisms between suspended sediment and active-layer sediment, as well as active-layer and subsurface sediment. The sediment mixture is represented through a suitable number of sediment size classes, and governing-equations’ terms are defined as size class–specific. Governing equations and associated numerical solutions are formulated within the general nonorthogonal curvilinear coordinate framework. A numerical solution is based on the fractional-step approach, using the characteristics method with higher-order interpolations for both flow and suspended-sediment advection steps. The numerical solution for equations describing a...

The dielectric permittivity of terrestrial ground ice formations: Considerations for planetary exploration using ground‐penetrating radar

Exploration of the polar ice caps and apparent glacial and periglacial landforms on Mars will aid our understanding of its ancient climate conditions and the history of water on the planet. Given that ground‐penetrating radar (GPR) is likely to be used to understand these features, we investigated the real component of the complex dielectric permittivity of stratified segregation ice, non‐stratified segregation ice, and polygonal ice wedge deposits in the Canadian Arctic. We acquired moveout profiles with a 450 MHz GPR on ground ice formations that had active layer sediments excavated prior to surveying. Using ice core data collected from these sites, we found that the volumetric fraction of ice plays the greatest role in defining the dielectric permittivity of the deposit and that it can be described using a modified complex refractive index method (CRIM) dielectric mixing model. Using the modified CRIM model, we estimate the dielectric permittivity of several ground ice deposits on Earth and present further estimates for similar features on Mars using permittivity values for Martian sediments derived from both theory and laboratory methods.

Micromorphology of periglacial sediments from the Tayara site, Qikirtaq Island, Nunavik (Canada)

Abstract Soil micromorphology provides an excellent resource for investigating Palaeoeskimo site-formation processes in the low arctic periglacial environment. In this study, micromorphology was used to answer questions concerning the composition, structure, origin and depositional agencies of the Tayara site active layer's sediments as well as to distinguish between natural (geogenic, biopedogenic) and cultural (anthropogenic) processes. Five groups of microfeatures were documented. These include 1) biopedological features (soil organic matter accumulation, mesofaunal and fungal activities), 2) transport-inherited features related to depositional processes (solifluction and stream sedimentation), 3) frost-induced microstructures and cryogenic features such as major post-depositional changes (ice-segregation, particle rearrangement, frost shattering, cryoturbation), 4) bone preservation in the active layer at the microscopic level, and 5) anthropogenic features related to Palaeoeskimo activities. The sediments from the three archaeological levels (I, IA and II) appear to have been very little influenced by anthropogenic factors. Cultural processes are micromorphologically observed in level II, with some evidence of feeding (bone presence), burning (wood charcoal, heated bone), and possibly trampling. However, the effects of natural processes on the sediments are more pronounced than anthropogenic ones.

Phosphatase and microbial activity with biochemical indicators in semi-permafrost active layer sediments over the past 10,000 years

Core samples of boreal terrestrial sediments from depths of 0–300 cm at Rikubetsu, Hokkaido, Japan were analyzed for alkaline and acid phosphatase enzymatic activities. Enzymatic activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) were greatest at the surface and decreased with depth; ALP and ACP activities were 25.5 and 22.0 nmol min −1 g −1, respectively, within the top 5 cm. These biological indicators were compared with measurements of microbial cell density and chemical indicators, including total organic C (TOC) and total hydrolyzed amino acids (THAA). The product–moment correlation coefficients ( r) for ALP and ACP versus microbial cell density were 0.949 and 0.810, respectively. The coefficients for THAA and TOC versus ALP were 0.997 and 0.995, respectively. Vertical distributions of enzymatic activity are highly consistent with the observed microbial biomass profile and diagenetic organic matter in the sediment. However, the vertical profile of PO 4 concentration shows a negative correlation coefficient for ALP and ACP of −0.937 and −0.855, respectively. Consequently, ALP and ACP were shown to be useful biomarkers of microbial activities in the terrestrial sediment over the past 10 ka at Rikubetsu, Hokkaido, Japan.

Groundwater hydrochemistry in the active layer of the proglacial zone, Finsterwalderbreen, Svalbard

Glacial bulk meltwaters and active-layer groundwaters were sampled from the proglacial zone of Finsterwalderbreen during a single melt season in 1999, in order to determine the geochemical processes that maintain high chemical weathering rates in the proglacial zone of this glacier. Results demonstrate that the principle means of solute acquisition is the weathering of highly reactive moraine and fluvial active-layer sediments by supra-permafrost groundwaters. Active-layer groundwater derives from the thaw of the proglacial snowpack, buried ice and glacial bulk meltwaters. Groundwater evolves by sulphide oxidation and carbonate dissolution. Evaporation- and freeze-concentration of groundwater in summer and winter, respectively produce Mg–Ca-sulphate salts on the proglacial surface. Re-dissolution of these salts in early summer produces groundwaters that are supersaturated with respect to calcite.There is a pronounced spatial pattern to the geochemical evolution of groundwater. Close to the main proglacial channel, active layer sediments are flushed diurnally by bulk meltwaters. Here, Mg–Ca-sulphate deposits become exhausted in the early season and geochemical evolution proceeds by a combination of sulphide oxidation and carbonate dissolution. At greater distances from the channel, the dissolution of Mg–Ca-sulphate salts is a major influence and dilution by the bulk meltwaters is relatively minor. The influence of sulphate salt dissolution decreases during the sampling season, as these salts are exhausted and waters become increasingly routed by subsurface flowpaths.