Search

The Laurentide Ice Sheet's (LIS) interior had a dynamic polythermal base, but the spatiotemporal variations of subglacial processes related to ice divide migration and other transient changes remain largely unknown, limiting our understanding of regional glacial dynamics. Previous studies focused on the regional glacial landform record, while ice sheet models lacked detailed parameterization within these regions, leading to an overestimation of cold-based subglacial conditions' extent and duration. In this study, glacial sediment dispersal patterns as identified by heavy minerals, clasts, and multivariate statistics of till matrix geochemistry were used to assess ice sheet dynamics within the Quebec–Labrador sector of the LIS. The earliest ice-flow phase produced and transported till across the study area (>175 km). However, major oxide data from till matrix geochemistry show a correlation with underlying bedrock, and this relationship is relatively common in areas of thin till cover and resistant bedrock lithologies. These results suggest a switch from an early phase of widespread erosion and long, sustained sediment transport to one of more limited erosion, perhaps abrasion dominant and shorter transport. Till compositional data and related dispersal patterns add supporting evidence to earlier ice sheet reconstructions based on ice-flow indicators and 10Be data together suggesting a transition from widespread uniform warm-based conditions during the earliest ice flow, followed by the development of an ice divide, its migration, and more sporadic warm-based conditions. Consequently, a thorough understanding of ice-flow history is essential for ice sheet modelling and future mineral exploration programs in inner ice sheet regions of the LIS. [ABSTRACT FROM AUTHOR]

The Newfoundland and Labrador Shelves Bioregion, located on the glaciated continental shelf and adjacent continental slope of eastern Canada, is classified into units that reflect its great physiographic diversity. There are ten shelf units: bedrock zone, fjord systems, major inlet, shelf-crossing troughs, four types of offshore banks, basin, and disturbed (glaciotectonic) terrain. There are three units on the continental slope: channelized areas, trough-mouth areas, and large sedimentary drifts. A series of vignettes illustrates both the distinguishing characteristics of the principal geomorphic units and the morphologic diversity within them. A sediment mobility analysis reveals that wave- and current-generated disturbances are dominant and largely depth-controlled within the shelf units, while the south-flowing Labrador Current impacts sediment transport and mobility along the continental slope. [ABSTRACT FROM AUTHOR]

Tidal flats are widely distributed on high-latitude coasts, where sea ice processes have been invoked to explain the abundance and distribution of boulders. This study documents the surface morphology and sediment dynamics of a Low-Arctic macrotidal system, the boulder-rich tidal flats of Koojesse Inlet, fronting the Nunavut capital, Iqaluit, on Baffin Island. This is a region of postglacial isostatic uplift and forced regression, with raised littoral, deltaic, and glaciomarine deposits. The spring-tidal range is 11.1 m and sea ice cover lasts roughly 9 months of the year. The extensive intertidal flats are up to 1 km wide, with a veneer of sand and gravel (including large boulders) resting on an erosional unconformity truncating the underlying glaciomarine mud, forming a terrace within the present tidal range. Over a 3-year study, no consistent pattern of erosion or deposition was evident. Over a longer time scale, the concave hypsometry, low sediment supply, slight ebb dominance of weak tidal currents, abrasion by wave-entrained sand, ebb-oriented ripples formed under subaerial drainage, and slumps on the terrace flanks are consistent with seaward hydraulic and gravitational sediment transport. These processes may be of greater importance than shoreward ice transport. This study underlines the importance of relict glaciomarine deposits, postglacial uplift, and falling relative sea level in the erosional development of these high-latitude tidal flats. Relative sea-level projections for Iqaluit are ambiguous, but a switch to rising sea level, if it occurs, combined with more open water and wave energy, could alter the foreshore dynamics of the system. [ABSTRACT FROM AUTHOR]

Impacts from a changing climate, in particular sea-level rise, will be most acutely felt on small oceanic islands. A common configuration of mid-latitude islands is the sandy barrier island. Sable Island, Nova Scotia, Canada is a vegetated sand island near the shelf edge, 160 km from the nearest point of land, that is morphologically similar to a barrier island. This study uses 60 years of airphoto records to analyse changes in coastline position through digitized shore and vegetation (foredune proxy) lines. Rates of coastal movement are analysed to model the future (2039) coastal configuration. The analyses suggest that the majority of the coastline on Sable Island is in retreat, with net retreat on the south side of the island only partially offset by modest net advance on the north side. The different morphologies of the beach–dune systems of South Beach and North Beach, driven by incident wind and waves, yield these different coastline responses. Projected loss of 10 ha by 2039 of the climax heath vegetative community to shoreline retreat suggests a trend toward island instability due to coastline migration. Island-wide data set trends show support for two different but complementary hypotheses about whole-island evolution: (1) the island is mobile via bank migration driving southern coastline changes and experiencing sediment transport toward the east, or (2) the island is generally immobile and losing subaerial sediments (and thus shrinking) likely due to ongoing (and accelerating) sea-level rise. [ABSTRACT FROM AUTHOR]

This study considers the influence of changing sea ice on nearshore sediment transport in the central north shore of Prince Edward Island, Southern Gulf of St. Lawrence. It is widely accepted that changing climate is causing sea ice to decrease in the region. Sea ice attenuates wave energy thereby reducing sediment transport. The Delft3D hydrodynamic model is used to simulate waves, currents, and sediment transport in seven sea ice concentration scenarios that can be differentiated into four classes: open water (<10%), low ice (10% to 35%), moderate ice (36% to 60%), and high ice (>60%). If ice concentration decreases from high to moderate, sediment transport is expected to increase 23%. Similarly, if ice concentration decreases from moderate to low, sediment transport is expected to increase a further 24%. If ice concentration decreases from low to open water conditions, sediment transport is expected to abruptly increase a further 85%. The increase in sediment transport as sea ice decreases from high concentration to open water conditions is 180%. Linear and power-law fits of sediment transport and sea ice concentration intersect at an ice concentration of 30%, indicating this value may be a useful threshold in planning for increased coastal erosion and developing appropriate adaptation strategies, in particular, adapting to increased sediment transport near tidal inlets and navigation channels. [ABSTRACT FROM AUTHOR]

The objective of this study is to verify whether low amounts of fine sand added to a muddy sediment matrix can be detected and quantified with accuracy using a Mastersizer 3000 (Malvern Panalytical) laser diffraction particle-size analyzer equipped with a Hydro LV large volume liquid dispersion module. To achieve this goal, a postglacial sediment sample was sieved to recover naturally co-occurring sand and clay–silt fractions. Sand in the range of 1%–7% by weight was added to the clay–silt at three concentrations (88, 132, and 276 mg dry weight) and each sample was duplicated. A very strong linear relationship was found between the measured % volume of sand added and the actual weight of sand added to the mud. Sand representing as low as 1% by weight could be detected. On average, there was only a 0.7% absolute difference between the measured and actual % sand values (range 0.02%–1.65%). Sample concentration had a negligible impact on the measured % sand. A range of plausible values for the refractive and absorption indexes, essential parameters for the Mie theory calculation of the size distribution from the measured light scattering, also had very small impact on the measured % sand. The demonstrated possibility of detecting a small input of fine sand to muddy sediment provides a basis for studies using grain-size data to reconstruct past and modern detrital inputs and sediment transport variations. [ABSTRACT FROM AUTHOR]

Elevated phosphorus (P) loading from the watersheds draining into Lake Erie, particularly from agricultural (53%) and urban (43%) sources, is identified as one of the main drivers of the severe eutrophication. In this study, we present a comprehensive evaluation of 11 process-based models to characterize the water cycle as well as nutrient fate and transport within a watershed context, and to find a robust and replicable way to optimize the modelling strategy for the Lake Erie watershed. Our primary objective is to review the conceptual/technical strengths and weaknesses of the individual models for reproducing surface runoff, groundwater, sediment transport, nutrient cycling, and channel routing, and to collectively guide the management of the Lake Erie Basin. Our analysis suggested that the available models either opted for simpler approximations of the multifaceted, nonlinear dynamics of nutrient fate and transport, and instead placed more emphasis on the advanced representation of the water cycle or, introduced a greater degree of biogeochemical complexity but simplified their strategies to recreate the roles of critical hydrological processes. Notwithstanding its overparameterization problem, the MIKE SHE model provides the most comprehensive 3D representation of the interplay between surface and subsurface hydrological processes with a fully dynamic description, whereby we can recreate the solute transport that infiltrates from the surface to the unsaturated soil layer and subsequently percolates into the saturated layer. Likewise, the physically based submodels designed to represent the sediment detachment and erosion/removal processes (DWSM, HBV-INCA, HSPF, HYPE, and MIKE SHE), offer a distinct alternative to USLE-type empirical strategies. The ability to explicitly simulate the daily plant growth (SWAT and APEX) coupled with a dynamic representation of soil P processes can be critical when evaluating the long-term watershed responses to various agricultural management strategies. Drawing parallels with the (sub)surface and sediment erosion processes, a more complicated physically based approach, e.g., the dynamic wave model provided by MIKE SHE (coupled with MIKE URBAN or MIKE HYDRO) and SWMM may be more appropriate for realistically simulating the pressurized flow and backwater effects of water routing in both open channels and closed pipes. While our propositions seem to favor the consideration of complex models that may lack the commensurate knowledge to properly characterize the underlying processes, we contend this issue can be counterbalanced by the joint consideration of simpler empirical models under an ensemble framework, which can both constrain the plausible values of individual processes and validate macroscale patterns. Finally, our study discusses critical facets of the watershed modelling work in Lake Erie, such as the role of legacy P, the challenges in reproducing spring-freshet or event-flow conditions, and the dynamic characterization of water/nutrient cycles under the nonstationarity of a changing climate. [ABSTRACT FROM AUTHOR]

Riverbanks undergo changes caused not only by river hydraulics, mainly sediment erosion and deposition processes, but also by the possible landslides that eventually change the channel bank profiles. Those failures are an important form of alluvial channel adjustments but are usually difficult to include during morphodynamic modeling. This paper proposes a novel approach combining a 2D depth-averaged hydrodynamic, sediment transport and mobile-bed model, SRH-2D, a limit equilibrium slope-stability model, BISHOP, and a bank failure sediment redistribution submodel, REDISSED, into a fully automatic and continuous dynamic simulation to predict vertical bed and lateral bank changes for a river reach undergoing exceptional flooding. The in-stream vertical fluvial changes predicted with the SRH-2D model will be automatically used to update the riverbank geometry profile by profile and assess their geotechnical stability to rotational slip failures with a developed slope-stability model based on Bishop's simplified method. A cone-shaped sliding area is defined in case the driving forces exceed the stabilizing forces. All mesh nodes located within the mass wasting zone will be automatically updated, allowing a new bank face form. The failed materials will be redistributed in the transect according to the geometry of the landslides observed at the study site. The Outaouais River at Notre-Dame-Du Nord, Quebec, is used to test the coupling procedure. Up to 100 m of bank retreat was predicted, and more than 20 cross-sections were reshaped. Typical results showing the effectiveness of the developed framework are presented and discussed. [ABSTRACT FROM AUTHOR]