Ice Scour Research Articles

The Influence of Pipeline-Backfill-Trench Interaction on Pipeline Response to Ice Gouging: A Numerical Investigation

Ice gouging is a destructive incident to subsea pipelines in Arctic regions. Trenching and backfilling is a cost-effective solution to physically protect the pipeline against ice gouging. Ice gouging imposes a complex combination of stresses and strains through the soil medium, the pipeline, and the interface. Remolded backfill materials with considerably less stiffness than native soil result in more complexity in soil failure mechanisms and pipe trajectories. However, this critical aspect is less explored in the literature on ice gouges. This paper investigated the influences of pipeline-backfill-trench interaction on the soil failure mechanisms and the pipeline responses by coupled Eulerian-Lagrangian (CEL) method. Two model configurations (shallowly buried and deeply buried pipeline) were set up to investigate the influence of trenching/backfilling, as well as pipe burial depth. Incorporation of the strain-rate dependency and strain-softening effects in the soil constitutive model involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. The research findings indicate that the conventional approach of assuming uniform seabed soil for trenched and backfilled pipelines may not accurately capture the pipeline behavior and soil failure mechanisms.

Layered seabed effects on buried pipeline response to ice gouging

In ice gouging analyses, the seabed is often simplified as a uniform material domain, over-looking the potential complexities inherent in layered seabed formations, which are wide-spread in numerous Arctic regions. This study investigates the pipeline response into the distinct seabed configurations, including layered soft over stiff clay, layered stiff over soft clay, and uniformly soft and uniformly stiff compositions, to ice gouging. This was achieved through comprehensive large deformation finite element (LDFE) analysis, employing a Coupled Eulerian Lagrangian (CEL) algorithm. Incorporation of the strain-rate dependency and strain-softening effects involved the development of a user-defined subroutine and incremental update of the undrained shear strength within the Abaqus software. The pipeline is explicitly incorporated into the model, allowing for a detailed investigation of its response to ice gouging phenomena within these layered seabed scenarios. This research demonstrates that simplifying a layered seabed into a uniform can be misleading. Such an approach can lead to significant errors, potentially overestimating or underestimating pipeline response to ice gouging. By incorporating these complexities, engineers can develop more optimized designs with enhanced safety margins in Arctic environments prone to ice gouging phenomena.

Lithological and mineralogical characteristic of the bottom sediments in the areas of ice scouring in the south-western Kara Sea

Lithological and mineralogical characteristic of the bottom sediments in the areas of ice scouring in the south-western Kara Sea

Glacial melt impacts carbon flows in an Antarctic benthic food web

Most coastal glaciers on the West Antarctic Peninsula are in retreat. Glacial ice scouring and lithogenic particle runoff increase turbidity and shape soft sediment benthic communities. This, in turn, has the potential to induce a shift in these systems from an autotrophic to a heterotrophic state. In this study, we investigated the influence of glacial runoff on carbon flows in the soft-sediment food web of Potter Cove, a well-studied shallow fjord located in the northern region of the West Antarctic Peninsula. We constructed linear inverse food web models using a dataset that includes benthic carbon stocks as well as carbon production and respiration rates. The dataset offers detailed spatial information across three locations and seasonal variations spanning three seasons, reflecting different degrees of disturbance from glacial melt runoff. In these highly resolved food web models, we quantified the carbon flows from various resource compartments (phytoplankton detritus, macroalgae, microphytobenthos, sediment detritus) to consumers (ranging from prokaryotes to various functional groups in meio- and macrofauna). Locations and seasons characterized by high glacial melt runoff exhibited distinct patterns of carbon flow compared to those with low glacial melt runoff. This difference was primarily driven by a less pronounced benthic primary production pathway, an impaired microbial loop and a lower secondary production of the dominant bivalve Aequiyoldia eightsii and other infauna in the location close to the glacier. In contrast, the bivalve Laternula elliptica and meiofauna had the highest secondary production close to the glacier, where they are exposed to high glacial melt runoff. This study shows how the effects of glacial melt propagate from lower to higher trophic levels, thereby affecting the transfer of energy in the ecosystem.

Behavioral analysis of seabed slope subjected to ice gouging

Ice gouging is a phenomenon that occurs when ice drifts to shallow depths due to current, wind and tides, thus resulting in a large deformation. Many previous studies have conducted numerical analysis based on centrifuge model experiment to understand the mechanism of ice gouging. Strain softening and rate dependence are the two important factors that influence ice gouging. However, the effect of these two important factors on the seabed subjected to large deformation was not considered in previous studies. Therefore, in this study, these factors are simulated, and the occurrence of large deformation in soil due to ice gouging is analyzed. In addition, numerical modeling based on two cases from among knowledge gained via various centrifuge model experiments is implemented. To simulate the large deformation of the soil, return mapping algorithm is applied to the ABAQUS subroutine VUMAT in conjunction with the formulas that define strain softening and rate dependence. These factors are reflected in ice gouging simulations and the consistency is reviewed by comparing and analyzing the results of the centrifuge model experiments implemented in previous studies. Based on this, the kinetic energy of ice keel is defined and a subroutine expressing kinetic energy reduction according to seabed soil resistance is additionally reflected. In addition, this method is applied to seabed slope in cold region to analyze the behavior of the slope.

Morphometric analysis of ice scour lakes in Iceland: A proxy for ice sheet dynamics

AbstractGlacial erosion rates on the Iceland landscape throughout the Pleistocene are not well quantified. Ice scour lakes provide an opportunity to investigate glacial erosive activity and relative intensity because they commonly form in areas beneath ice sheets due to intense quarrying. This study evaluates ice scour lake morphology and density as a potential proxy for paleo‐ice flow direction and basal thermal regime for parts of the Iceland Ice Sheet. Using GIS analysis, properties of ice scour lakes are examined in regions that experienced different rates of ice flow during and following the Last Glacial Maximum (LGM), as interpreted from streamlined subglacial landforms. The primary input datasets were topographic, hydrologic and bedrock data. Lake distribution and morphology were quantified for all natural lakes of Iceland (n = 30 169), with close examination of three 400 km2 sub‐regions in Vestfirðir (n = 904), Húnaflói (n = 69) and Bakkaheiði (n = 232). Lake distribution parameters include density, packing and centroid elevation. PolyMorph‐2D was used to quantify lake morphology including orientation, area and elongation ratio. Ice scour lake density, packing and elevation were all greatest on Vestfirðir. The high density and packing of lakes across Vestfirðir suggests unique ice dynamics relative to the other two sub‐regions, and multidirectional flow of lake axes supports the presence of an independent ice cap covering Vestfirðir. Differential intensity of glacial erosion interpreted from regions of high and low lake density on Bakkaheiði supports a proposed ice divide in Northeast Iceland. The orientation of lakes align with the flow directions of proposed LGM ice streams in Northern and Northeast Iceland. Ice scour lakes were most elongate on average on Bakkaheiði, which supports fast ice flow. Improving understanding of former ice sheet basal thermal regime and paleo‐ice flow velocity serves to inform modern controls on ice sheet stability and ice sheet basal processes.

Pb-210 Dating of Ice Scour in the Kara Sea

Ice scours are formed when the keels of floating icebergs or sea ice hummocks penetrate unlithified seabed sediments. Until now, ice scours have been divided into “relict” and “modern” according to the water depth that corresponds with the possible maximum vertical dimensions of the keels of modern floating icebergs. However, this approach does not consider climatic changes at the present sea level, which affect the maximum depth of ice keels. We present an application of 210Pb dating of the largest ice scour in the Baydaratskaya Bay area (Kara Sea), located at depths of about 28–32 m. Two sediment cores were studied; these were taken on 2 November 2021 from the R/V Akademik Nikolay Strakhov directly in the ice scour and on the “background” seabed surface, not processed via ice scouring. According to the results of 210Pb dating, the studied ice scour was formed no later than the end of the Little Ice Age. Based on the extrapolation of possible sedimentation rates prior to 1917 (0.22–0.38 cm/year), the age of the ice scour is estimated to be 1810 ± 30 AD. The mean rate of ice scour filling with 70 cm thick sediments from the moment of its formation is around 0.33 cm/year.

Strong correlations of sea ice cover with macroalgal cover along the Antarctic Peninsula: Ramifications for present and future benthic communities

Macroalgal forests dominate shallow hard bottom areas along the northern portion of the Western Antarctic Peninsula (WAP). Macroalgal biomass and diversity are known to be dramatically lower in the southern WAP and at similar latitudes around Antarctica, but few reports detail the distributions of macroalgae or associated macroinvertebrates in the central WAP. We used satellite imagery to identify 14 sites differing in sea ice coverage but similar in terms of turbidity along the central WAP. Fleshy macroalgal cover was strongly, negatively correlated with ice concentration, but there was no significant correlation between macroinvertebrate cover and sea ice. Overall community (all organisms) diversity correlated negatively with sea ice concentration and positively with fleshy macroalgal cover, which ranged from around zero at high ice sites to 80% at the lowest ice sites. Nonparametric, multivariate analyses resulted in clustering of macroalgal assemblages across most of the northern sites of the study area, although they differed greatly with respect to macroalgal percent cover and diversity. Analyses of the overall communities resulted in three site clusters corresponding to high, medium, and low fleshy macroalgal cover. At most northern sites, macroalgal cover was similar across depths, but macroalgal and macroinvertebrate distributions suggested increasing effects of ice scour in shallower depths towards the south. Hindcast projections based on correlations of ice and macroalgal cover data suggest that macroalgal cover at many sites could have been varying substantially over the past 40 years. Similarly, based on predicted likely sea ice decreases by 2100, projected increases in macroalgal cover at sites that currently have high ice cover and low macroalgal cover are substantial, often with only a future 15% decrease in sea ice. Such changes would have important ramifications to future benthic communities and to understanding how Antarctic macroalgae may contribute to future blue carbon sequestration.

Numerical modeling of ice–seabed interaction in layered soil: stiff over soft clay

This study presents a numerical investigation of free field ice gouging in layered cohesive seabeds comprising stiff over soft clay. A three-dimensional, half-space, dynamic large deformation finite element analysis was conducted using the Coupled Eulerian Lagrangian approach. To simulate the seabed, a Tresca soil model with the strain rate and strain-softening effects was coded into a user subroutine. The accuracy of the model was verified by comparing its results with those of published experimental studies. Additionally, a comprehensive parametric study was conducted to examine the effect of various ice gouging scenarios and seabed soil parameters on the subgouge soil deformation and the ice keel reaction forces. Our findings revealed that an interactive response occurs between the soil layers and the ice keel that may cause the peak subgouge soil deformation and keel reaction magnitudes to differ from those observed under uniform soil condition. The developed model was found to be an efficient tool for free field ice gouging analysis in cohesive layered seabeds.

Lithological and Geochemical Indicators of Ice Gouging: Evidences from Holocene Sediments in the East Siberian Sea

Abstract —Cores of Holocene bottom sediment collected in the East Siberian Sea revealed layers with mixed textures and layers with breaks in sedimentation corresponding to the two sea levels defined as modern (upper) and Early Holocene (lower). The layers are characterized by distinctly chaotic variability in textural pattern (mottled appearance, multidirectional banding), colorimetric and geochemical parameters (sawtooth-like distribution curves). Such character of changes is associated with the physical action of dragging keels of ice/icebergs exerted on the seafloor and is referred to as ice gauging (scouring). Its analysis can be used for identification of ice scour-affected layers in other sediment cores collected in this region, and for the purpose of creating a representative database, predicting their occurrence and developing adequate measures to minimize the damaging impact from drifting sea ice and icebergs on the seafloor within the bounds of the Arctic shelf.

Deformation of trenched multilayer pipelines during large lateral displacement due to subsea geohazards

Large lateral displacement of trenched multilayer pipelines may be induced by ground movement, landslides, ice gouging, etc. The significant difference between the shear strength of the backfill material and the native soil may affect the pipeline-backfill-trench interaction, the failure mechanisms, and consequently the lateral soil resistance. However, this challenging and less-explored aspect has not been covered thoroughly in design codes, even for rigid pipes. This paper investigates the influences of multilayer pipeline-backfill-trench interaction on the deformation of pipe section, soil failure mechanism, resultant lateral soil resistance, and soil pressure on the pipe by large deformation finite element analyses. A decoupled model consisting a Coupled Eulerian-Lagrangian (CEL) approach with a rigid pipe in ABAQUS was created along with a finite element (FE) model of multilayer flexible pipe in ANSYS to assess their relative merits for this problem. A parametric study was conducted to investigate the influences of key factors, including the trench geometry, stiffness of backfill material, native seabed soil properties, burial depth, and intensity of pipeline-trench bed interaction. The study showed that the ignorance of the pipeline-backfill-trench interaction by using uniform soil might result in underestimation and overestimation of the lateral soil resistance at different displacement amplitudes.

Drift Algal Accumulation in Ice Scour Pits Provides an Underestimated Ecological Subsidy in a Novel Antarctic Soft-Sediment Habitat.

Ice scouring is one of the strongest agents of disturbance in nearshore environments at high latitudes. In depths, less than 20 m, grounding icebergs reshape the soft-sediment seabed by gouging furrows called ice pits. Large amounts of drift algae (up to 5.6 kg/m2) that would otherwise be transported to deeper water accumulate inside these features, representing an underestimated subsidy. Our work documents the distribution and dimensions of ice pits in Fildes Bay, Antarctica, and evaluates their relationship to the biomass and species composition of algae found within them. It also assesses the rates of deposition and advective loss of algae in the pits. The 17 ice pits found in the study area covered only 4.2% of the seabed but contained 98% of drift algal biomass, i.e., 60 times the density (kg/m2) of the surrounding seabed. Larger ice pits had larger and denser algal accumulations than small pits and had different species compositions. The accumulations were stable over time: experimentally cleared pits regained initial biomass levels after one year, and advective loss was less than 15% annually. Further research is needed to understand the impacts of ice scouring and subsequent algal retention on ecosystem functioning in this rapidly changing polar environment.

The response of layered seabed to ice gouging: Sand over clay

Travelling icebergs may threaten the structural integrity of the offshore pipelines in any territories they can reach. Arctic offshore pipelines are usually buried for physical protection against ice gouging. The safe and cost-effective burial depth of these pipelines needs to be determined by accurately assessing the subgouge soil deformation and the ice keel-seabed contact forces. Layered seabed soil strata found in many geographical locations add to the complexity of assessing the ice keel-seabed interaction process. The currently used design codes have been developed for uniform soil strata-an assumption that may affect the accuracy and cost-effectiveness of the design. In this study, the significance of layered sand over clay seabed in the ice gouging process was investigated by performing large deformation finite element (LDFE) analysis using Coupled Eulerian-Lagrangian (CEL) approach. A comprehensive parametric study was conducted to assess the influence of ice gouging characteristics and soil properties on the subgouge soil deformation, the developed plastic shear strains, and the resultant ice keel reaction forces. The results showed that the seabed response to ice gouging largely depends on the soil strata, where the layers’ interaction effects can alter the usual response expected from a uniform seabed.

Comparison of macroalgae meadows in warm Atlantic versus cold Arctic regimes in the high-Arctic Svalbard

A warmer Arctic with less sea ice will likely improve macroalgae growth conditions, but observational data to support this hypothesis are scarce. In this study, we combined hydroacoustic and video inspections to compare the depth of growth, density and thickness of macroalgae (>10 cm) meadows in two contrasting climate regimes in Svalbard 1) the warm, ice free, Atlantic influenced West Spitsbergen and 2) the cold, Arctic and seasonal ice covered East Spitsbergen. Both places had similar insolation and comparable turbidity levels. Macroalgae communities at both places were similar and were formed mainly by common north Atlantic kelp species: Saccharina latissima, Alaria esculenta, Laminaria digitata and L. hyperborea. However, the density of the bottom coverage and thalli condition were strikingly different between the two sites. Algae at the warmer site were intact and fully developed and occupied most of the available hard substrate. At the colder site, only patchy macroalgae canopies were found and most thallies were physically damaged and trimmed at a uniform height due to physical ice scouring. These differences in macroalgal density and thalli condition were only found at depths down to 5 m. Deeper, no distinct differences were observed between the warm and cold sites. Sea urchins were only observed at the warm site, but in few numbers with no visible negative top-down control on macroalgae growth.

Biogeography of algae and invertebrates from wave-exposed rocky intertidal habitats along the Atlantic coast of Nova Scotia (Canada): Latitudinal and interannual patterns and possible underlying drivers

Biogeographic studies aim to understand species distributions and are becoming increasingly relevant to establish baselines to monitor ecological change. The NW Atlantic coast hosts a cold-temperate biota, although knowledge about its biogeography is patchy. This study documents for the first time biogeographic variation at mid-to-high intertidal elevations in wave-exposed rocky intertidal habitats along the open Atlantic coast of Nova Scotia (Canada), a hydrographically distinct subregion of this cold-temperate region. For this goal, we measured the summer abundance of algae and invertebrates at the same nine locations over four consecutive years (2014 to 2017) spanning 415 km of coastline, which allowed us to examine latitudinal and interannual patterns. In addition, we looked for mensurative evidence on possible drivers underlying these patterns, focusing on sea surface temperature, daily maximum and minimum temperature (which often happen at low tides at thus differ from sea surface temperature), pelagic food supply for intertidal filter-feeders (phytoplankton abundance and particulate organic carbon), drift sea ice during the cold season (which can cause intertidal disturbance), and species associations. Our field surveys revealed that northern locations can be severely disturbed by ice scour when drift ice is abundant and, while biological recolonization occurs over the years, it differs in pace among locations. Southern locations, instead, did not experience ice scour during our study and, thus, generally exhibited a higher species richness and abundance than northern locations. Multivariate analyses indicated that the aforementioned expressions of temperature and pelagic food supply explained together 32–55% of the variation in alongshore biogeographic pattern, depending on the year. Species association analyses suggest that algal foundation species (generally more abundant at southern locations) contribute to increase location-wise species richness. Mensurative evidence for bottom-up forcing in seaweed–herbivore and filter-feeder–predator systems differed greatly among years. Overall, in addition to its inherent value to advance NW Atlantic intertidal biogeography, our species distribution database should be valuable to assess ecological change decades into the future as climate change and other anthropogenic influences unfold.

Impact of Local Scour around a Bridge Pier on Migration of Waved-Shape Accumulation of Ice Particles under an Ice Cover

The migration of a waved-shape accumulation of ice particles under an ice cover (referred to as “ice wave” in this study) is a phenomenon of transport of ice particles during an ice accumulation process in rivers. The migration of an ice wave will affect the pier scour. On the other hand, the local scour at the pier will affect the migration of ice waves. The interaction between the migration of ice waves and local scour around a pier is a very complicated process since not only the channel bed deforms, but also the ice jam develops simultaneously. By conducting a series of flume experiments, the interaction between the local scour around bridge piers and the migration of ice waves was studied. By applying both continuity and momentum equations, an empirical equation has been derived for predicting the thickness of ice waves around the pier. The impacts of the scour hole on the thickness of ice waves around the pier have been studied. The thickness of the wave crest and the migration speed of ice waves have been investigated. Similar to a scour hole in a sand bed, an “ice scour hole” appeared at the bottom of the ice jam around the pier. The existence of the “ice scour hole” affects the development of ice waves. A formula for calculating ice transport capacity has been obtained. Results calculated using the derived formula are in good agreement with those of laboratory experiments.

Heterogeneities in the Upper Part of the Section of the East Siberian Sea Sedimentary Cover: Gas Accumulations and Signs of Ice Gouging

Heterogeneities in the Upper Part of the Section of the East Siberian Sea Sedimentary Cover: Gas Accumulations and Signs of Ice Gouging

Опасные газонасыщенные объекты на акваториях Мирового океана: Восточно-Сибирское море

For the first time, the researchers performed the interpretation of the upper part of the common depth point (CDP) seismic sections in the northwestern part of the East Siberian Sea (ESS) along the 44 lines of JSC MAGE in the amount of 8200 km. They revealed 129 anomalous objects in near-bottom sediments, potentially associated with gas accumulations and channels of its subvertical migration. The average distance between these objects along the lines was 63.6 km — 5.2—6.2 times less than in the Chukchi, Laptev and Bering seas. The authors substantiate that the ESS is characterized by a significantly smaller number of gas migration channels — active faults reaching the near-bottom sediments, compared to the seas mentioned above. This is consistent with the lower neotectonic activity of the ESS and the absence of significant seismic events. In the study area, the researchers revealed a large number of depressions in the bottom relief, which are associated with the furrows of ice gouging during the transgressions-regressions of the sea and at the present stage. Significant errors in the GEBCO bathymetry database were also revealed.

Numerical Modeling of Ice–Seabed Interaction in Clay by Incorporation of the Strain Rate and Strain-Softening Effects

Abstract Ice gouging is one of the main threats to the safety of the subsea pipelines buried in Arctic coastal regions. Determining the best pipeline burial depth relies on free-field ice gouging analysis and obtaining the resultant subgouge soil deformations. Therefore, improving the accuracy and efficiency of the free-field ice gouging analysis is a key demand in daily engineering practice. The pressure-induced by ice keel through the ice gouging process causes the seabed soil to undergo large localized plastic deformation, where the classical Lagrangian method confronts mesh instability challenges. Also, the conventional Mohr–Coulomb soil model is not able to account for the strain-rate dependency and strain-softening effects, which are significant in ice gouging event. In this study, free-field ice gouging in clay was simulated using a coupled Eulerian–Lagrangian approach. The strain-rate dependency and strain-softening effects were incorporated by developing a user-defined subroutine and incremental updating of the undrained shear strength in abaqus. The comparison of the model predictions with published numerical and experimental studies showed a significant improvement of accuracy. A comprehensive parametric study was also conducted to investigate the effect of various model parameters on the seabed response to ice gouging.

The Extremes of Disturbance Reduce Functional Redundancy: Functional Trait Assessment of the Shallow Antarctic Benthos

Climate-driven changes in disturbance are a major threat to ecosystem Functional diversity. The selective mechanisms underlying ecosystem response to disturbance are far from universal and remain the subject of scientific debate. Ice scouring of the shallow Antarctic benthos is one of the largest disturbance gradients in the natural environment and thus provides an opportunity to investigate how disturbance gradients influence functional structure of a biological assemblage. The Western Antarctic Peninsula, in particular, is a hotspot of climate-driven environmental change. Addressing how this system might respond to species loss is critical. Previous surveys across the shallowest 100 m of the seabed, detected unimodal changes in diversity and a shift in assemblage composition in response to disturbance gradients. This study investigated how functional traits and associated functional diversity change across the depth gradient. Our results revealed that selective mechanisms, such as disturbance filtering and inter-species competition, reduce functional redundancy at the extremes of the disturbance gradient. Our study highlights areas of potential vulnerability to future environmental change due to low functional redundancy. Threatening the important negative (mitigating) feedbacks on climate change, through blue carbon, currently provided by Antarctic continental shelf benthic assemblages.