High Sediment Concentrations Research Articles

Effects of microplastics on the rheological properties of sediment slurries in aquatic environments

Sediment slurries, characterized by their high concentrations of fine-grained cohesive sediment, are prevalent in various aquatic environments, including fluid mud, sediment gravity flows, and dredging slurries. Abundant microplastics have been detected in sediment slurries, which indicates that these slurries function as carriers for the transport of microplastics. However, there is a dearth of understanding on how sediment slurries transport microplastics. To ascertain the transport mechanisms, elucidating the effects of microplastics on the rheological properties of sediment slurries is a prerequisite because these properties govern the flow dynamics and mobility of such slurries. This study conducts experimental and theoretical investigations to examine, interpret, and quantify the effects of microplastics on the rheological properties of sediment slurries. Microplastics are shown to increase the yield stress and viscosity of sediment slurries via enhancing sediment aggregation. A new descriptor, specifically, the effective volume fraction, is proposed to characterize the effects of microplastics on sediment aggregation. Based on the newly-proposed descriptor, a new analytical model is proposed to predict the yield stress and viscosity of sediment slurries with microplastics. This study lays a foundation for further interpretating the flow dynamics and thus the transport processes of sediment slurries laden with microplastics.

Numerical investigation on erosion characteristics of elevated pile cap in high concentration sediment flow environment

Numerical investigation on erosion characteristics of elevated pile cap in high concentration sediment flow environment

Deglaciation in the subtropical Andes has led to a peak in sediment delivery

Glaciers are thinning and retreating as climate warms, thus eroding less of the Earth’s surface. However, other hydrological factors in glacierized catchments are likely producing a transient increase in sediment delivery, resulting in ‘peak sediment’. Estimating the trajectory of the peak sediment is ecologically and socially important but scientifically challenging because of the delayed and non-linear response of glacier sediment export to climate forcing. This study used time series of suspended sediment concentration starting in the 1960s from 11 Andean rivers at subtropical latitudes to analyse past changes in sediment export and infer its future behaviour. The recent decade has experienced anomalously high sediment concentration in most glacierized catchments, but the 1970s experienced even higher values. Decadal variations in the relationship between sediment concentration and ice melt suggest that the magnitude of the current decade was lower due to reduced glacial sediment rather than other factors. Combining this result with the fact that glacial runoff is decreasing, it is inferred that, for most of the glacierized catchments, the peak sediment generated by the anthropogenic deglaciation started two centuries ago has already passed its maximum.

Water Column Nitrogen Removal During Storms in a Low‐Order Watershed

AbstractWater column removal in streams is a nitrogen (N) cycling pathway that has been historically overlooked. Studies filling this knowledge gap have focused on the role of water column N removal in mid‐to‐large‐order rivers with consistently high suspended sediment concentrations. However, smaller streams may provide comparable suspended sediment concentrations during and after storm events, creating favorable conditions for water column N removal. To assess the presence, magnitude, and control of water column N removal during storms in low‐order watersheds, we measured water column denitrification and heterotrophic assimilatory N uptake rates at three locations in a Mid‐Atlantic watershed during five storm events of different magnitude, sediment loads, and nutrient availability. We found large variations in water column denitrification (0–5.56 mg N g−1 d−1) and assimilatory uptake (0.003–1.67 mg N g−1 d−1). Higher rates of N removal occurred during flow recession, with a correlation between suspended sediment organic matter content and denitrification. On average, denitrification rates in the water column were higher when flashy responses to storm events occurred. In contrast to denitrification, water column N removal rates (as both denitrification and heterotrophic assimilation) during storm events were comparable to those measured at baseflow in larger rivers. However, water column denitrification could only account for less than 10% of potential reach‐scale N removal during most of the storm events. Our findings provide insight into the ecological relevance of small stream water columns and suggest that more research is needed to understand the magnitude of stream water column processing on watershed‐scale N removal.

Numerical investigation for the influence of suspended sediment on salinity distribution in the Qiantang Estuary, China

Numerous studies have demonstrated that high suspended sediment concentration (SSC) can change density distribution and affect water mixing, but few scholars have investigated this impact on numerical simulations of estuarian salinity distribution. The Qiantang Estuary is a macro-tidal estuary with high SSC, which has a more significant influence on water density than that of salinity. Therefore, this paper established a three-dimensional (3D) numerical model coupling flow, salinity and SSC based on Delft3D and first analyzes the impact of SSC on salinity distribution under different runoff and tidal conditions in the Qiantang Estuary. The results indicated that simulated salinity generally decreases when considering the impact of SSC, suggesting a weakening effect on saltwater intrusion. The distribution of salinity difference (ΔS) and SSC show a strong spatial and temporal correlation, and ΔS peak increases and shifts upstream as the tidal range increases or runoff discharge decreases. The mechanism of SSC influencing saltwater intrusion can be summarized as follows: On the one hand, SSC increases the water density, which weakens the driving force for saltwater to move upstream, causing a decrease in flood current velocity and water level, and thereby diminishing the advective transport of salinity. On the other hand, SSC enhances density stratification, which weakens vertical turbulence and reduces the dispersive transport of salinity. These combined effects reduce both the advective and diffusive salinity fluxes during the flood tide, ultimately leading to a decrease in upstream salinity. Therefore, neglecting this effect in estuaries with high SSC can cause significant deviations in salinity simulation results, especially under low-flow and high-tide conditions.

Photocatalysis: A Sustainable Approach for Removing Hazardous Polyaromatic Hydrocarbons

AbstractPolycyclic aromatic hydrocarbons (PAHs) are omnipresent toxic pollutants found in numerous ecosystems, including soil, water, and living organisms. Due to their hydrophobic nature, PAHs tend to accumulate in aquatic environments, leading to high concentrations in aquatic sediments and subsequent bioaccumulation in organisms. This accumulation poses substantial risks to humans and aquatic life. Recent advances in photocatalytic methods, particularly those using nanocomposite materials, have shown promising outcomes in the degradation of PAHs. Photocatalysis, a process that uses UV and visible light to accelerate a chemical reaction, is effectively breaking these harmful compounds. This review focuses on the recent advances in the degradation of PAHs, the toxicological effects of PAHs on living organisms, and the mechanisms underlying nanocomposite‐based photocatalysis. The utilization of nanocomposite for photocatalysis is an eco‐friendly substitute to traditional methods for remediating PAH pollution in the ecosystem. This green approach using nanocomposite‐based photocatalysis offers a sustainable and effective approach for the degradation of PAHs.

Impact of seasonal variations in fronts on suspended sediments transport off the coastal area of Fujian Province

The Zhejiang-Fujian (Zhe-Min) coastal muddy area plays a crucial role in facilitating sediment exchange through a cross-front. The mud depocenter off the Zhe-Min coastal area is a source of suspended sediment that can be transported to the continental shelf of the East China Sea (ECS). Although the front of the inner shelf of the ECS has been extensively reported, the cross-front material transport off the coastal area of Zhe-Min in summer has not been well studied, especially using measured data. To reveal how the front controls the transport of suspended sediment, this study focuses on the impact of fronts on the dispersion of suspended sediment off the coastal area of Fujian Province in different seasons. The results indicate that the front acts as a barrier, inhibiting the dispersion of suspended sediment into the sea. The high-concentration suspended sediment is mainly found to the northwest of the front, with an average SSC of 8.5 mg/L in winter and 3.1 mg/L in summer. The suspended sediment concentration (SSC) follows a V-shaped distribution along the cross-isobath transects, with lower SSC observed at the 50-m isobath compared with the shallow water area and the deep water area. The SSC at the front was the lowest, with an average concentration of 2.3 mg/L in winter and 1.9 mg/L in summer. The front is crucial for the development of the Zhe-Min coastal muddy area. The winter monsoon is strong, resulting in a sufficient supply of suspended sediments in the muddy area and a high transport flux of suspended sediments in the nearshore. The front hinders the dispersion of high-concentrated sediment from the nearshore to the offshore, resulting in the deposition of fine-grained sediments in the nearshore and the formation of an inner shelf muddy sedimentary zone. The findings of this study will help improve our understanding of the sediment source-to-sink processes in the ECS and land–sea interactions.

Regime Shift to Hyperturbid Conditions in the Loire Estuary: Overview of Observations and Model Analysis of Physical Mechanisms

AbstractThe Loire estuary (France) was extensively deepened during the 20th century. Coincidentally, suspended sediment concentrations increased drastically from ∼0.1 g/l to ∼1–5 g/l at the surface and the estuarine turbidity maximum (ETM) moved upstream. In this study we, for the first time, brought together a century of observations of estuary bed level, tidal amplitude, and sediment concentration to demonstrate these large changes. Next, we analyzed a minimal set of physical mechanisms that explain the dramatic increase in sediment concentration. To this end, we used the iFlow model representing dynamic equilibrium conditions in the Loire. Novel in the model is that it dynamically resolves salt stratification and corresponding damping of turbulence. For conditions representing the year 2000, high sediment concentrations were found with satisfactory correspondence to observations. Low sediment concentrations were found when using the year 1900 bed level but keeping all other model parameters the same. Varying the bed level gradually between these two extremes, the equilibrium solution suddenly increases for intermediate bed level, constituting an abrupt regime shift. Robustness of this result was established in an extensive sensitivity study featuring 13,200 model experiments. The regime shift is enabled by a feedback between increasing sediment concentration, reducing turbulence due to sediment and salt stratification, and increasing sediment importing capacity of the estuary. The essential sediment importing mechanisms in this feedback are related to the tidal asymmetry and gravitational circulation. This is the first time gravitational circulation and salt stratification are shown to be important factors in a transition to hyperturbidity.

Numerical and experimental study on water-sediment flow in a lateral pumping station forebay

Multiple vortex flow patterns are commonly observed in lateral pumping station forebays, particularly in basins with high sediment concentrations. These patterns can lead to pump blockage, sediment deposition, and other issues that disrupt pump station operations. The water-sediment two-phase flow in lateral pumping station forebays is significantly influenced by the start-up combination, yet our understanding remains limited. To address this, the mixture multiphase flow theory is introduced to describe water-sediment dynamics, and the mathematical model is validated with experimental data. By analyzing the characteristics and formation mechanisms of large vortex and multiple small vortex regions in the original scheme, nine different start-up combination schemes were proposed. The research results indicate that, due to the narrow channel and slope effect in the lateral forebay, some of the gravitational potential energy of the water-sediment mixture is converted into kinetic energy upon entering the forebay, thereby increasing the velocity in the main flow area. Additionally, due to the friction and dissipation effects of the two sidewalls, a pressure difference is generated in the main flow area, resulting in the formation of multi-level vortices. Furthermore, the various types of proposed start-up combinations can optimize the flow patterns in the forebay to a certain extent. The preferred scheme improved the uniformity of flow velocity by 18.63% and increased the deviation angle by 17.62°, resulting in a 75.47% reduction in vortex area compared to the original scheme. These research results provide theoretical guidance for optimizing start-up combinations and reorganizing flow field structures to achieve hydrodynamic dredging effects.

What do glass sponges do when no one is looking? Vazella pourtalesii: Responses to sediment deposition, passive locomotion, and contracting behavior

Behavioral response of deep-sea sponges can provide crucial insights into the mechanisms shaping energy fluxes and ecosystem functioning. Although some advances have been made, the behavior of deep-sea Hexactinellid still remain widely unknown. In the present study we address the glass sponge Vazella pourtalesii behavior. High-temporal resolution imaging and environmental data were acquired with an autonomous lander deployed in the Sambro Bank Sponge Conservation Area (Scotian Shelf) at a depth of 150 m, representing the upper limit of this deep-sea species' distribution and what is commonly regarded as the deep sea.For 94 days, a V. pourtalesii individual was monitored, providing quantitative information on its response to sediment deposition triggered by a storm, as well as on its passive locomotion and contractive behavior. Sediment was cleared from its surface within 72 h, which is highly relevant for its filtering capacity, indicating that this sponge species can cope with high suspended sediment concentrations. This enables it to occur on sedimentary environments like the Scotian Shelf. As observed in other deep-sea hexactinellids, the monitored individual engaged in rhythmic contractions, which appear to be driven by physiological process/es rather than environmental factors. During the study period, strong bottom currents (>37 cm/s) toppled and displaced the monitored individual several times. Despite changes in position and orientation that can negatively impact the filtering capacity of sponges, no signs of deterioration were observed. V. pourtalesii's vase-like body morphology and attachment to cobbles, as a gravitational center, may allow it to have a more homogeneous interaction with currents which may permit them to better cope with positional changes. Overall, this study highlights that deep-sea Porifera display a wide array of phenological changes in response to both biotic and abiotic factors.

Sediment remobilization over subaqueous sand waves: In-situ observation in the northern South China Sea

High-resolution tripod observations were conducted in a subaqueous sand-wave field in the northern South China Sea. The objective was to gain insight into the dynamic mechanism by which sandy sediments are remobilized by oceanic dynamic processes, in particular internal solitary waves and internal tides. Daily-recurring high suspended sediment concentrations were observed, likely due to lateral transport of sediments resuspended by critical reflection of diurnal internal tides at the shelf break. The passage of extreme internal solitary waves results in resuspension of sediments from the seabed and ejection of these sediments out of the boundary layer. The resuspension of sediments from the seabed is controlled by current-induced strong bed shear stress, while the ejection of sediments out of the bottom boundary layer is driven by the compression and subsequent expansion of the mixing layer, together with the developments of the separation bubbles behind the internal solitary waves. These findings provide new insights into understanding the dynamic mechanism of sediment remobilization by internal solitary waves. Moreover, they contribute to our understanding of the migration of subaqueous sand waves.

Degradation of pyrene at high concentrations in sediment and the implications for the microbiome in microbial electrochemical systems

The polycyclic aromatic hydrocarbons (PAHs) frequently accumulate in sediments, particularly those near industrial sites. The efficacy of microbial electrochemical systems (MESs) in electricity generation and PAHs degradation is intricately linked to the microbiome’s response to high contaminant levels. Metabolomics and metagenomics were applied to elucidate the impact of a high pyrene concentration on the functional structure and metabolic dynamics of sediment microbiomes within MES. In sediment with a high pyrene concentration, both the electrical output of MES and efficiency of their microbiomes in degrading organic substrates and pyrene were markedly reduced. These conditions were associated with the enrichment of PAH-degrading microorganisms, such as Hydrogenophaga and Flavobacterium. Analyses of metabolites and genetic profiles revealed that metabolic pathways were primarily influenced in MES exposed to low pyrene concentrations whereas fewer metabolic pathways were activated in MES exposed to high concentrations; instead, pathways representing functions critical for microbial survival and communication were activated as well. According to enzymatic analyses, low pyrene levels promoted carbohydrate metabolism by sediment microorganisms, whereas high levels had an inhibitory effect. An examination of electron transport enzymes revealed that intracellular electron transfer was facilitated by both low and high concentrations. However, high levels impeded enzymes associated with outer membrane electron transfer, hindering electron movement from intracellular to extracellular electron acceptors and thus negatively affecting the electrical output of MES. Our study provides crucial theoretical insight and mechanistic understanding for addressing the challenges that may be encountered when MES are used to treat pyrene-contaminated sediment near industrial sites.

The Emu Bay Shale: A unique early Cambrian Lagerstätte from a tectonically active basin.

The Emu Bay Shale (EBS) of South Australia is anomalous among Cambrian Lagerstätten because it captures anatomical information that is rare in Burgess Shale-type fossils, and because of its inferred nearshore setting, the nature of which has remained controversial. Intensive study, combining outcrop and borehole data with a compilation of >25,000 fossil specimens, reveals that the EBS biota inhabited a fan delta complex within a tectonically active basin. Preservation of soft-bodied organisms in this setting is unexpected and further underscores differences between the EBS and other Cambrian Lagerstätten. Environmental conditions, including oxygen fluctuations, slope instability, high suspended sediment concentrations, and episodic high-energy events, inhibited colonization of the lower prodelta by all but a few specialist species but favored downslope transportation and preservation of other largely endemic, shallow-water benthos. The EBS provides extraordinary insight into early Cambrian animal diversity from Gondwana. These results demonstrate how environmental factors determined community composition and provide a framework for understanding this unique Konservat-Lagerstätte.

Numerical simulation of submarine landslide tsunamis based on the smoothed particle hydrodynamics model

This paper establishes a SPH (Smoothed Particle Hydrodynamics) model for simulating underwater landslides based on the mixture theory. This model requires only one layer of particles, which greatly improves the computational efficiency compared with the traditional two-layer particle simulation for a mixture theory scheme. In the numerical model, based on a mixture theory, submerged landslide flow is regarded as a mixture of water and sediment phases and is discretized into a series of SPH mixed particles employing the volume fraction of the sediment phase. Using this volume fraction, a convection–diffusion term is calculated to represent the material transport between the water phase and the sediment phase. In addition, based on this volume fraction, the SPH mixed particles at any location in the considered domain are classified into three categories: (i) pure water, (ii) low-concentration suspended sediment, and (iii) high-concentration sediment. Pure water is treated as a Newtonian fluid. High-concentration sediment is modeled as a non-Newtonian fluid, and the Herschel–Bulkley–Papanastasiou rheological model is used to describe the viscous forces. The viscosity of the low-concentration suspended sediment, which acts as a transition layer between pure water and high-concentration sediment, is derived from the Chezy relation. A comparison of the numerical and experimental results demonstrates the high accuracy of the present numerical scheme. Using this validated numerical model, underwater landslides are simulated. Specifically, the effects of landslide deformation and compaction degree on the amplitudes of the surge wave crest and trough are investigated.

A typical point bar with atypical strata in the McMurray Formation, Alberta, Canada: Floods, tides and high suspended sediment concentrations

AbstractStratigraphic positions and the nature of some breccias and mudstones observed in the Lower Cretaceous McMurray Formation type section (Alberta, Canada) challenge the existing fluvial point bar facies models. The currently applied large‐scale, tidally influenced, sandy bedload facies model suggests that point bars fine upward, where breccias and cross‐strata occur at the base of the succession and mud content increases upward. Instead, this study documents that: (i) mudstone clast breccias are not exclusively associated with basal channel‐lag deposits and can occur throughout the point bar; and (ii) stratified mudstones are not limited to the top of the fining‐upward succession and can occur at or near the channel base. This outcrop data, including lithology, sedimentary structures, trace fossils, bed thickness and boundaries, and the nature of stratal packages, further suggests dynamic interplay between fluvial and tidal processes. This article discusses the potential role of high‐magnitude river floods in temporarily elevated suspended sediment concentrations and highlights that fluid mud processes played a crucial role in mud deposition in both tide‐influenced and fluvial parts of the system. Fluid mud processes allowed mud deposition along the channel base and across the point bar accretion surfaces. The breccias predominantly consist of broken pieces of inclined heterolithic strata and mostly occur on accretion sets of point bars, suggesting erosion and collapse of the point bar rather than of the cutbank. This work introduces a novel perspective to the existing models of point bar sedimentation, offering a new end member and concepts for the interpretation of subsurface data. The authors hope that this research encourages further investigations into similar phenomena elsewhere in the world.

Application of artificial countermeasures to enhance desilting efficiency in a reservoir under normal and extreme events

ABSTRACT The influx of flood-induced turbidity flows with high sediment concentrations into the reservoir can create sediment deposition issues, potentially jeopardizing water supply reliability. Efficient management of reservoir water resources is imperative for sustainable utilization. Evaluating the need for reservoir desilting involves comprehending the inflow and outflow dynamics of water-sediment discharges, the capacity of existing outlet structures, reservoir operation objectives, and available desilting technologies. However, given the altering hydrological conditions due to the impacts of climate change, there is a necessity for adaptive methods to ensure reservoir storage maintenance. Consequently, this study introduces the utilization of a flushing channel with artificial guiding structures to enhance desilting efficiency. A 2D numerical model offers convenient computational tools for assessing water-sediment transport behaviors across various operational scenarios based on reservoir management strategies. Data obtained from field observations is collected and analyzed to calibrate and verify the numerical model. By employing 2D numerical modeling, sediment concentration and desilting efficiency are calculated to support effective desilting operations within a reservoir. Simulation results indicate that the integration of additional artificial guiding structures at the bottom of the reservoir can enhance sedimentation mitigation outcomes by approximately 17.63% under normal conditions and by 5.27% under extreme hydrological conditions.

Observation of high sediment concentrations entrained in jumble river ice

AbstractIce formation is generally considered to exclude many particles and most solutes and thus be relatively pure compared to ambient waters. Because river ice forms by a combination of thermal and mechanical processes, some level of sediment entrainment in the ice column is likely, though reports of sediment in river ice are limited. We observed high and sporadic levels of silt and sand in ice of the Kuskokwim and Tanana rivers (Alaska, the United States) during routine field studies. These observations led us to make a more comprehensive survey of sediment entrainment in river ice of the Kuskokwim and Yukon rivers and several of their tributaries. We collected and subsampled 48 ice cores from 19 different river locations in March 2023, which included concurrent measurements of water turbidity, velocity, and depth. Approximately 60% of cores contained detectable levels of sediment, averaging 438 mg/L with median concentrations exceeding 1000 mg/L in three cores from the Yukon and Kuskokwim main stems. Many cores had even higher concentrations at certain intervals, with seven cores having subsamples exceeding 2000 mg/L; these were often located in the middle or lower portion of the ice column. Jumble ice, formed mechanically by frazil‐pan jamming during freeze‐up, was generally the best predictor of higher sediment entrainment, and these locations often had higher under‐ice velocities and depths. Our observation of high and widespread sediment entrainment in northern river ice, particularly in jumble‐ice fields, may have implications for sediment transport regimes, ice strength and transportation safety, and how rivers break up in the springtime.

Development and application of an integrated methodology for post‐disaster field investigation of debris floods

AbstractDebris floods commonly occur in steep channels with an abundant sediment supply, and they can cause significant damage, primarily due to their higher sediment concentrations and negative impacts upon bank erosion, deep scouring and aggradation. These key hazards pose challenges for traditional assessment methods, making quantification difficult. This became obvious during a recent catastrophic debris flood that occurred on July 12, 2022, in the Heishuigou catchment (102 km2), northern Sichuan Province, China. In this case study, we developed an integrated methodology for assessing this debris flood event by incorporating field surveys, hydrological and hydraulic modelling and sediment transport calculations. Detailed information such as topographic maps, photographs, deposits, grain size distributions and inundation depths was collected to analyse the material sources, validate the parameters and conduct model calculations. The peak debris flood discharge and the supra‐critical bed shear stress ratios, estimated from hydrological and dynamic models, were incorporated to analyse the debris flood's typology and characterize its destructive mechanisms. The regional frequency–volume relationship established through bedload transport calculations was calibrated using the volume of the deposits determined via field investigation. These methods not only contribute to a comprehensive understanding of debris floods but also provide valuable support for future risk assessments and mitigation designs.

Contrasting platinum trajectories in three major French rivers using dated sediment cores (1910–2021): From geochemical baseline to emerging source signals

Platinum (Pt) is a Technology Critical Element (TCE) which, since the 1990s, has been mainly used in the industry in catalytic converters for automobile emission control. Previous studies have shown Pt contamination of road-side sediments and surface sediments in urban rivers and lakes but few of them have addressed temporal variations. The present work presents historical Pt concentration trends in 137Cs-dated sediment cores from floodplains or secondary channels at the outlets of three major French watersheds (Loire, Rhone, and Seine Rivers) covering the past ∼110 years, i.e., from the 1910s to 2021. Platinum baseline levels in the sediment were estimated for the Loire River (0.76 ± 0.22 μg kg−1 for the period ∼1910-∼1955) and the Rhone River (1.64 ± 0.41 μg kg−1), and historical Pt variations seem to reflect variations in hydrodynamics and grain size composition. Since the early 2000s, Pt concentrations in the Loire and the Rhone River sediments tend to increase (>2.5 μg kg−1) and were attributed to the use of car catalytic converters, an emerging technology since the 1990s using >50 % of European Pt demand. High and variable historical Pt concentrations (up to 14.6 μg kg−1) in the Seine River sediments may reflect legacy Pt sources due to former anthropogenic activities in this watershed, such as the use of Pt-based catalysts for petroleum refinery since the end of the 1940s, coal handling and precious metals refining, probably concealing the likely presence of an emerging traffic-related Pt signal. This first comparison of historical Pt concentration trends in sediments from contrasting watersheds allows to distinguish signals originating from different natural and anthropogenic sources (background level, historical sources, road traffic).

Pockmarks Offshore Big Sur, California Provide Evidence for Recurrent, Regional, and Unconfined Sediment Gravity Flows

AbstractRecent surface ship multibeam surveys of the Sur Pockmark Field, offshore Central California, reveal >5,000 pockmarks in an area that is slated to host a wind farm, between 500‐ and 1,500‐m water depth. Extensive fieldwork was conducted to characterize the seafloor environment and its recent geologic history, including visual observations with remotely operated vehicles, sediment core sampling, and high‐resolution, near‐bottom Chirp and multibeam surveys collected with autonomous underwater vehicles to capture the morphology and stratigraphy of the pockmarks. No evidence of high methane concentrations in sediments, chemosynthetic biological communities, or methane‐derived diagenetic byproducts was found. Chirp data and sediment cores showed alternating layers of slowly accumulating hemipelagic drapes interrupted by more reflective turbidite horizons that extend throughout the pockmark field and beyond. Chirp data showed multiple episodes of lateral migration over time in some of the pockmarks in association with erosion and infilling events. Laterally continuous turbidite horizons that overlay erosional surfaces indicated that pockmark migration occurred synchronously in multiple pockmarks separated by tens of kilometers. These shifts are presumed to be the result of asymmetrical erosion of the pockmark flanks caused by passing sediment gravity flows. While some pockmarks occur in chains, most are not clustered or randomly spaced but are regularly dispersed within the pockmark field. We hypothesize that intermittent, unconfined sediment gravity flows occurring over at least the last 280,000 years are the source of the regionally continuous turbidite deposits and the mechanism that maintained the regularly dispersed pockmarks.