Abstract Sediments on Arctic continental shelves are impacted by sea ice and ice‐related processes for up to 9 months per year. As a result, seabed morphology in cold regions can exhibit features such as ice scours which are absent on lower‐latitude shelves. Previous literature has provided rich qualitative and some quantitative assessments of keel scours and strudel scours (i.e., feature density) in pan‐Arctic settings. However, based on a recent multibeam survey along >600 km of tracklines in Harrison Bay, Alaska, Arctic shelves can exhibit a much greater diversity of interesting morphologic features. In this paper we present an atlas of seabed features and some geotechnical properties observed across a 60 × 90 km portion of the Alaskan Beaufort Shelf, with the goal of highlighting the great diversity of Arctic continental‐shelf seabed morphologies. We applied a combined approach of modern geomorphologic and geotechnical analysis of Arctic seabed environments, including: (a) machine learning algorithms applied to keel scour data, in order to better describe densities, geometries, and orientations at different water depths; and (b) portable free‐fall penetrometer measurements collected at high spatial densities, in order to better characterize the geotechnical seabed properties associated with keel scour. Together this information about Arctic shelf seabed morphologies and applications of emerging quantitative tools to Arctic settings provides an advance in our understanding of Arctic seascape from a geotechnical and textural perspective.

Continental shelves serve as repositories and transition zones for terrigenous sediments. Wave energy, sea ice coverage, and sediment delivery (from eroding coasts and rivers) all influence sediment storage and morphology on Arctic shelves, but the locations and accumulation rates of sediment depocenters (hotspots of accumulation) across large regions of Arctic shelf systems, including the Alaskan Beaufort Shelf, are not well-constrained. Sediment transport and storage is expected to change in light of increasing wave energy and reduced seasonal sea-ice coverage. To better contextualize sedimentation on the shelf in light of changing environmental forcing parameters, we studied sediment and erosion dynamics in Harrison Bay, Alaska, using Pb-210 activity profiles from sediment cores and bathymetric change detection. Meter-scale seabed elevation change was measured across the inner shelf over the past 70 years, including hotspots of up to ~3 m of vertical change on the subaqueous Colville River Delta and near Cape Halkett (a prominent headland). This likely represents a combination of erosion and seafloor subsidence due to subsea permafrost degradation. Erosion of the inner shelf is consistent with predictions made in the 1980s of shelf backstepping, meaning that the shelf is translating landward (and possibly at an accelerating rate) in response to coastal retreat. Rates of bathymetric change tapered to near zero for much of the middle shelf, apart from a small zone in central Harrison Bay where elevations increased by up to 1 m. Therefore, a small depocenter appears to exist, but in general sediment seems to bypass the shallow parts of the shelf on multidecadal timescales. These findings form a baseline for predicting future morphologic change, including seafloor erosion, amid increasingly energetic Arctic sea states.

Arctic coastlines are known to be rapidly eroding, but the fate of this material in the coastal ocean (and the sedimentary dynamics of Arctic continental shelves in general) is less well-constrained. This study used summertime mooring data from the Alaskan Beaufort Shelf to study sediment-transport patterns which are dominated by waves and wind-driven currents. Easterly wind events account for most of the seasonal sediment transport, and serve to focus sediment on the inner shelf. This is a key finding because it means that sediment is readily available for wave-driven resuspension and sea-ice entrainment during fall storms. Sediment-ice entrainment has been previously implicated as a major mechanism for Arctic Shelf erosion-and so the summertime focusing of sediment observed in this study may actually serve to enhance shelf erosion rather than promote shelf sediment accumulation. In a pan-Arctic context, the Alaskan Beaufort Shelf is somewhat similar to the Laptev Sea Shelf, where previous work has shown that sediment is also focused during the summer months (but for different reasons related to estuarine-like circulation under the Laptev plume). The Alaskan Beaufort Shelf example contrasts with previous work on the Canadian Beaufort Shelf, where dominant winds from the opposite direction (northwest) likely promote strong seaward dispersal of sediment rather than inner-shelf convergence. This study thus highlights the importance of understanding dominant wind patterns when considering seasonal and inter-annual storage, transport, and erosion of sediments from Arctic continental shelves.

Geomechanical data of Arctic nearshore and offshore seabed sediments remain sparse. Two field surveys were conducted in Harrison Bay, Alaska, in the summers of 2021 and 2022. These surveys involved portable free-fall penetrometer (PFFP) deployments, grab sampling, gravity coring, and compressed high-intensity radar pulse sonar for seabed investigation and bathymetric surveying. The goals of this study were to test geomechanical seabed surface sediments in situ using a PFFP, relate those properties to erodibility parameters from a jet erosion test (JET), and demonstrate the potential use of geomechanical seabed mapping to better inform numerical models of shelf morphological evolution in an Arctic environment. After deriving the firmness factor (FF) from the PFFP data, a classification scheme was developed with an FF = 450 m-1 threshold differentiating cohesive and noncohesive sediments at a threshold fines content of 30%. Strength properties were then calculated for cohesive or noncohesive sediments, respectively. For noncohesive sediments, the packing state in the form of relative density was related to the JET-derived detachment coefficient, kd, with the critical shear stress being determined via empirical relations. Three categories were assigned for cohesive sediments: an undrained shear strength separator of su = 2 kPa correlated well with groupings of kd obtained from JET performed on gravity core samples, and the third category for the least erosive sediments was developed for su values greater than 20 kPa. These categories helped explain variability in erodibility and sediment strength across the entire bay and a focused 13 km transect on the inner shelf. Recently deposited sediment from bluff erosion and ice-scoured seabed were both classified in the highest erodibility group, highlighting the usefulness of this classification system for studying morphodynamics in Arctic environments.

Providing opportunities for early career researchers to gain leadership experiences in seagoing oceanographic science is critical to maintaining an inclusive and robust research community. While various opportunities exist to attract early career scientists to oceanography through undergraduate research experiences or first-time access to seagoing science, there are notable gaps in helping junior researchers who are already in the oceanographic workforce (junior faculty, research scientists, postdoctoral scholars) step into and embrace leadership roles. This training gap is particularly acute for leadership in field science, especially for remote regions with complicated logistics and unfamiliar platforms and support structures, notably the Arctic and Antarctic. In light of rapid environmental changes occurring at the poles and the importance of these regions in global connectivity, polar-specific training is needed to ensure incoming generations can effectively plan and execute research on icebreakers and ice-capable vessels. Here, we describe two training efforts conducted in 2023 and 2024 specifically tailored to train future leaders in polar seagoing science.

Through the Sediment, Ice, & Learning on the Tanana (SILT) project, a team of university scientists engaged two middle school student groups in testing innovative environmental research technologies to measure sediment flowing underneath river ice.The culturally responsive, place-based pilot program tests these technologies as a strategy to increase students' science interest and science self-efficacy.Over a series of three workshops, 39 students built and deployed low-cost turbidity sensors to measure sediment flowing underneath river ice and designed model payload attachment systems to attach the sensors to drones for measuring sediment fluxes during spring river ice breakup.Students' changes in science interest and self-efficacy were measured using both a true pre-and post-program survey and a retrospective pre-program survey.

Sediments covering Arctic continental shelves are uniquely impacted by ice processes. Delivery of sediments is generally limited to the summer, when rivers are ice free, permafrost bluffs are thawing, and sea ice is undergoing its seasonal retreat. Once delivered to the coastal zone, sediments follow complex pathways to their final depocenters-for example, fluvial sediments may experience enhanced seaward advection in the spring due to routing under nearshore sea ice; during the open-water season, boundary-layer transport may be altered by strong stratification in the ocean due to ice melt; during the fall storm season, sediments may be entrained into sea ice through the production of anchor ice and frazil; and in the winter, large ice keels more than 20 m tall plow the seafloor (sometimes to seabed depths of 1-2 m), creating a type of physical mixing that dwarfs the decimeter-scale mixing from bioturbation observed in lower-latitude shelf systems. This review summarizes the work done on subtidal sediment dynamics over the last 50 years in Arctic shelf systems backed by soft-sediment coastlines and suggests directions for future sediment studies in a changing Arctic. Reduced sea ice, increased wave energy, and increased sediment supply from bluffs (and possibly rivers) will likely alter marine sediment dynamics in the Arctic now and into the future.

Sediment discharged from the Greenland Ice Sheet delivers nutrients to marine ecosystems around Greenland and shapes seafloor habitats. Current estimates of the total sediment flux are constrained by observations from land-terminating glaciers only. Addressing this gap, our study presents a budget derived from observations at 30 marine-margin locations. Analyzing sediment cores from nine glaciated fjords, we assess spatial deposition since 1950. A significant correlation is established between mass accumulation rates, normalized by surface runoff, and distance down-fjord. This enables calculating annual sediment flux at any fjord point based on nearby marine-terminating outlet glacier melt data. Findings reveal a total annual sediment flux of 1.324 + /− 0.79 Gt yr-1 over the period 2010-2020 from all marine-terminating glaciers to the fjords. These estimates are valuable for studies aiming to understand the basal ice sheet conditions and for studies predicting ecosystem changes in Greenland’s fjords and offshore areas as the ice sheet melts and sediment discharge increase.

Ice 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.

ICESat-2’s Advanced Topographic Laser Altimeter System (ATLAS) has emerged as useful tool for calculating attenuation signals in natural surface waters, thus improving our understanding of particulates from open-ocean plankton to nearshore suspended terrigenous sediments. While several studies have employed methods based on Beer’s Law to derive attenuation coefficients (including through a machine-learning approach), a rigorous sensitivity test on specific tuning parameters and processing choices has not yet been performed. Here we present comprehensive sensitivity tests of solar background removal, noise removal, choice of bin sizes, surface-peak exclusion, and beam pairing across four contrasting marine environments as well as two contrasting daytime/nighttime examples to quantify the impact of these processing choices on the derived photon-based attenuation coefficient Kdph. Horizontal and vertical bin sizes caused 6-13% variation in results, and adjusting the starting depth for calculations (i.e., the exclusion depth for the noisy sea-surface peak) caused 17% variation in results. Pairing data from strong and weak beams caused ~6-11% variation in results. In some environments, daytime data could be reasonably salvaged, but in others the results were not reliable. Detailed information about processing choices and a suggested workflow for ocean applications are provided. The sensitivity test results and suggested workflow pave the way for expanded Kdph analyses of global datasets (including turbid coastal waters) as well as interdisciplinary applications, such as evaluating nearshore ecological processes related to sediment dynamics and light attenuation.

Capes and cape-associated shoals represent sites of convergent sediment transport, and can provide points of relative coastal stability, navigation hazards, and offshore sand resources. Shoal evolution is commonly impacted by the regional wave climate. In the Arctic, changing sea-ice conditions are leading to (1) longer open-water seasons when waves can contribute to sediment transport, and (2) an intensified wave climate (related to duration of open water and expanding fetch). At Blossom Shoals offshore of Icy Cape in the Chukchi Sea, these changes have led to a five-fold increase in the amount of time that sand is mobile at a 31-m water depth site between the period 1953-1989 and the period 1990-2022. Wave conditions conducive to sand transport are still limited to less than 2% of the year, however - and thus it is not surprising that the overall morphology of the shoals has changed little in 70 years, despite evidence of active sand transport in the form of 1-m-scale sand waves on the flanks of the shoals which heal ice keel scours formed during the winter. Suspended-sediment transport is relatively weak due to limited sources of mud nearby, but can be observed in a net northeastward direction during the winter (driven by the Alaska Coastal Current under the ice) and in a southwestward direction during open-water wind events. Longer open-water seasons mean that annual net northeastward transport of fine sediment may weaken, with implications for the residence time of fine-grained sediments and particle-associated nutrients in the Chukchi Sea.

Seasonal sea ice impacts Arctic delta morphology by limiting wave and river influences and altering river-to-ocean sediment pathways. However, the long-term effects of sea ice on delta morphology remain poorly known. To address this gap, 1D morphologic and hydrodynamic simulations were set up in Delft3D to study the 1500-year development of Arctic deltas during the most energetic Arctic seasons: spring break-up/freshet, summer open-water, and autumn freeze-up. The model focused on the deltaic clinoform (i.e., the vertical cross-sectional view of a delta) and used a floating barge structure to mimic the effects of sea ice on nearshore waters. From the simulations we find that ice-affected deltas form a compound clinoform morphology, that is, a coupled subaerial and subaqueous delta separated by a subaqueous platform that resembles the shallow platform observed offshore of Arctic deltas. Nearshore sea ice affects river dynamics and promotes sediment bypassing during sea ice break-up, forming an offshore depocenter and building a subaqueous platform. A second depocenter forms closer to shore during the open-water season at the subaerial foreset that aids in outbuilding the subaerial delta and assists in developing the compound clinoform morphology. Simulations of increased wave activity and reduced sea-ice, likely futures under a warming Arctic climate, show that deltas may lose their shallow platform on centennial timescales by (a) sediment infill and/or (b) wave erosion. This study highlights the importance of sea ice on Arctic delta morphology and the potential morphologic transitions these high-latitude deltas may experience as the Arctic continues to warm. The shape of a river delta is affected by river, wave, and tidal forces. In the Arctic, the presence of seasonal sea ice is also thought to play an important role in shaping high-latitude deltas. To investigate the effects of sea ice on Arctic delta shape, we used a popular computer model with a new representation of sea ice to examine delta growth. Our results showed that sea ice limits delta growth near the shoreline, but accelerates growth further away at sea. It leads to a large underwater platform, which is consistent with the morphology (shape) of Arctic deltas. The results were used to test future Arctic warming conditions when a reduction in sea ice coverage is likely. Future modeled simulations showed that Arctic deltas may lose the shallow underwater platform from increases in infilling by river sediments or increases in wave erosion. These results shed light on the impacts sea ice has on shaping Arctic deltas and potential changes that may occur to these delta systems as the Arctic continues to warm. 1D Delft3D simulations of delta growth under sea-ice show compound clinoform development Nearshore sea-ice promotes sediment bypassing and the development of a shallow subaqueous topset (2-m deep) Arctic deltas may lose the shallow 2-m-deep topset if future sea ice coverage continues to decline and river and wave influence grows

Estuaries worldwide have been altered by anthropogenic modifications including land clearing, dredging, and land reclamation, which impact sediment routing and accumulation on tidal flats. Numerous studies have explored tidal flat and marsh vulnerability to submergence or “drowning” under accelerating sea-level rise, but recent work along the Oregon coast suggests estuaries are maintaining positive accretionary balances (at least in marshes) despite ongoing sea-level rise. In this study, accretion rates (sediment accumulation rates) were evaluated from 210Pb profiles at eight sites on broad intertidal flats in Coos Bay, one of the largest estuaries on the U.S. West Coast and a site of substantial development and logging since the mid-1800s. Based on the century-scale record of sediment accretion represented by 210Pb profiles, tidal flats have been accreting at rates of 1–3 mm/yr with little spatial relationship to relative sea-level rise or patterns of tectonic uplift. Thus, accretion is generally not accommodation- or supply-limited, and therefore likely not regulated by sea-level rise. Peaks in sediment accretion are well-preserved from the last 30 years, and accretion rates averaged over this more modern time span tend to be four times greater than rates averaged over the whole-core (century-scale) 210Pb records. It is unclear whether the higher, more modern rates represent a real change in estuarine accretion patterns over the past decades or a Sadler effect (i.e., an apparent but not real increase in accretion in younger sediments). The results highlight the spatial variability in accretion rates within a single estuary, the potential resiliency of this tectonically active estuary to sea-level rise (in the form of a positive accretionary balance), and raise the issue of whether management decisions are best made based on century-scale accretion rates or multi-decadal accretion rates.

Open-source designs for turbidity and depth sensors are becoming increasingly capable and available, but the knowledge required to construct them limits their use compared with expensive, commercial sensors. Here we present an open-source optical backscatter and water pressure sensor that can be ordered almost fully assembled, requires no coding to deploy and costs approximately 50 USD. We share three examples of these sensors’ ability to facilitate new research. First, we observed complex changes in spatial and temporal patterns of suspended sediment transport in the Arctic Sagavanirktok River using a network of sensors. Second, we measured turbidity during the freeze-up period in the Tanana River, a period of high risk to sensors. Last, we built and deployed sensors with middle-school students to monitor turbidity under full ice cover on the Tanana River. The success of open-source sensors in these examples shows a marked increase in scale and accessibility of river science.

Himalayan lakes represent critical water resources, culturally important waterbodies, and potential hazards. Some of these lakes experience dramatic water-level changes, responding to seasonal monsoon rains and post-monsoonal draining. To address the paucity of direct observations of hydrology in retreating mountain glacial systems, we describe a field program in a series of high altitude lakes in Sagarmatha National Park, adjacent to Ngozumba, the largest glacier in Nepal. In situ observations find extreme (>12 m) seasonal water-level changes in a 60-m deep lateral-moraine-dammed lake (lacking surface outflow), during a 16-month period, equivalent to a 5 × 10^6 m ^3 volume change annually. The water column thermal structure was also monitored over the same period. A hydraulic model is constructed, validated against observed water levels, and used to estimate hydraulic conductivities of the moraine soils damming the lake and improves our understanding of this complex hydrological system. Our findings indicate that lake level compared to the damming glacier surface height is the key criterion for large lake fluctuations, while lakes lying below the glacier surface, regulated by surface outflow, possess only minor seasonal water-level fluctuations. Thus, lakes adjacent to glaciers may exhibit very different filling/draining dynamics based on presence/absence of surface outflows and elevation relative to retreating glaciers, and consequently may have very different fates in the next few decades as the climate warms.

Abstract Avulsions change river courses and transport water and sediment to new channels impacting infrastructure, floodplain evolution, and ecosystems. Abrupt avulsion events (occurring over days to weeks) are potentially catastrophic to society and thus receive more attention than slow avulsions, which develop over decades to centuries and can be challenging to identify. Here, we examine gradual channel changes of the Peace‐Athabasca River Delta (PAD), Canada using in situ measurements and 37 years of Landsat satellite imagery. A developing avulsion of the Athabasca River is apparent along the Embarras River–Mamawi Creek (EM) distributary. Its opening and gradual enlargement since 1982 are evident from multiple lines of observation: Between 1984 and 2021 the discharge ratio between the EM and the Athabasca River more than doubled, increasing from 9% to 21%. The EM has widened by +53% since 1984, whereas the Athabasca River channel width has remained stable. The downstream Mamawi Creek delta is growing at a discharge‐normalized rate roughly twice that of the Athabasca River delta in surface area. Longitudinal global navigation satellite systems field surveys of water surface elevation reveal the EM possesses a ∼2X slope advantage (8 × 10−5 vs. 4 × 10−5) over the Athabasca River, and unit stream power and bed shear stress suggest enhanced sediment transport and erosional capacity through the evolving flow path. Our findings: (a) indicate that a slow avulsion of the Athabasca River is underway with potentially long‐term implications for inundation patterns, ecosystems, and human use of the PAD; and (b) demonstrate an observational approach for identifying other slow avulsions at river bifurcations globally.

AbstractFrontal ablation, the combination of submarine melting and iceberg calving, changes the geometry of a glacier's terminus, influencing glacier dynamics, the fate of upwelling plumes and the distribution of submarine meltwater input into the ocean. Directly observing frontal ablation and terminus morphology below the waterline is difficult, however, limiting our understanding of these coupled ice–ocean processes. To investigate the evolution of a tidewater glacier's submarine terminus, we combine 3-D multibeam point clouds of the subsurface ice face at LeConte Glacier, Alaska, with concurrent observations of environmental conditions during three field campaigns between 2016 and 2018. We observe terminus morphology that was predominately overcut (52% in August 2016, 63% in May 2017 and 74% in September 2018), accompanied by high multibeam sonar-derived melt rates (4.84 m d−1 in 2016, 1.13 m d−1 in 2017 and 1.85 m d−1 in 2018). We find that periods of high subglacial discharge lead to localized undercut discharge outlets, but adjacent to these outlets the terminus maintains significantly overcut geometry, with an ice ramp that protrudes 75 m into the fjord in 2017 and 125 m in 2018. Our data challenge the assumption that tidewater glacier termini are largely undercut during periods of high submarine melting.

Climate change will increase the duration of annual sea‐ice‐free periods and shift precipitation patterns across the Arctic. Those factors are likely to increase erosion rates along its coasts. Large parts of the Arctic coast consist of hard rock. However, glacial, deltaic, and coastal sedimentary deposits occur in deglaciated areas and isostatic uplift following glaciations has created beach ridge plains and pocket beaches with coarse soft‐sediment cliffs. Hitherto, very little was known about the spatial distribution, erosion rates, and morphodynamics of soft sediment cliffs along the coast of Greenland. Here, we investigate a 3‐km sedimentary cliff section on the south coast of Qeqertarsuaq (Disko Island). We measured 2D cliff top erosion over 50 years between 1964 and 2014 as well as 3D cliff profile change over 2 years between 2019 and 2021. Morphometric indices of the gravel beach and cliff were calculated based on a series of cross‐shore elevation profiles. Wave run‐up at the beach fronting the cliff was modeled with XBeach‐G for a series of storm events under present day sea‐ice conditions and for a reduced sea‐ice scenario. Cliff top erosion rates varied along the cliff with maximum rates of 0.3 m y −1 . The investigated coastal cliff erodes by two coupled processes: (a) precipitation‐driven surface runoff downslope the cliff and (b) wave‐driven erosion at the cliff toe. In a continuously warming climate, this study shows that erosion of soft coastal cliffs in Greenland thus can accelerate due to increased storminess and prolonging open water periods.