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Abstract 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. 

Abstract 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. 

Abstract 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 (a) longer open‐water seasons when waves can contribute to sediment transport, and (b) 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. 

Abstract Observations of ocean surface waves at three sites along the northern coast of Alaska show a strong correlation with seasonal sea ice patterns. In the winter, ice cover is complete, and waves are absent. In the spring and early summer, sea ice retreats regionally, but landfast ice persists near the coast. The landfast ice completely attenuates waves formed farther offshore in the open water, causing up to a two‐month delay in the onset of waves near shore. In autumn, landfast ice begins to reform, though the wave attenuation is only partial due to lower ice thickness compared to spring. The annual cycle in the observations is reproduced by the ERA5 reanalysis product, but the product does not resolve landfast ice. The resulting ERA5 bias in coastal wave exposure can be corrected by applying a higher‐resolution ice mask, and this has a significant effect on the long‐term trends inferred from ERA5. 

Six small coastal moorings were deployed in Harrison Bay for approximately 30 days between early August and early September. Two moorings were outfitted with Nortek Aquadopps and optical backscatter sensors and the remainder were outfitted with RBR sensors which recorded some combination of salinity, temperature, pressure, and turbidity. All sensors were mounted within approximately 0.5 meters (m) of the bed to capture boundary-layer dynamics. Turbidity values were converted to total suspended solids concentrations. Wave parameters (significant wave height, peak wave period, and wave direction) were post-processed from Aquadopp data. Shear velocities (used in sediment-transport research) were calculated from current and wave data at the sites where Aquadopps were mounted. Data have been used in support of a publication, "Summertime sediment convergence on the Alaskan Beaufort Shelf and implications for ice rafting." 

This dataset includes water-column data collected from the Beaufort Shelf during the open-water seasons in 2020, 2021, and 2022. The 2020 data include water-column profiles (salinity, temperature, depth, turbidity, particle size distributions, particle volume concentrations, and uncorrected clorophyll-a) collected with an RBR CTD/Tu (conductivity, temperature, depth, turbidity) sensor and LISST sensor from R/V Sikuliaq and its workboat. Most sites were in the Harrison Bay region (north of the Colville Delta and Simpson Lagoon) and a few were located farther east. The 2021 and 2022 data include the same CTD/Tu and LISST data that were collected in 2020, but are focused in Harrison Bay and also include profiles of light intensity (photosynthetically active radiation) as well as ADCP (acoustic doppler current profile) profiles from a pole-mounted Nortek Signature 500 kilohertz (kHz) sensor. In 2021, additional data include filtration data (total suspended solids, suspended sediment concentrations, and organic fractions) from water samples and hi-resolution echosounder data from the Nortek ADCP. These data are being incorporated into publications about summertime water-column properties and sediment transport dynamics within Harrison Bay (Eidam et al., pending). 

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. 

This dataset includes vessel-based water-column profile and seabed data collected around Blossom Shoals, a shoal complex offshore of Icy Cape in northwestern Alaska (in the Chukchi Sea). Data were collected from the Research Vessel (R/V) Sikuliaq (offshore) and a companion workboat (inshore). Water-column profile data include salinity, temperature, depth, and turbidity data collected using a RBR Maestro CTD/Tu (conductivity, temperature, depth, turbidity) sensor package. Profile data also include median diameters and volumetric concentrations of suspended particles, where were collected using a Sequoia LISST200X (laser in situ scattering transmissometer). Seabed grab samples were collected from the Sikuliaq using a shipek grab sampler and from the workboat using a hand-operated mini van veen grab sampler. Samplers were bagged and returned chilled to the lab for particle-size analyses in an Escitec Bettersizer S3Plus laser diffraction sensor. Sediments were not treated for organics due to generally low organic contents. Samples contained primarily sand except for a few isolated locations where mud was found. Data were collected in November 2019 during the fall freezeup season when pancake ice were beginning to form. Data were also collected in late September and early October 2020 during a mooring recovery cruise. Single-beam bathymetry data (which were only collected in 2020) were gathered using a commercial fish finder mounted on the workboat and connected to a data logger. 

This file contains grain-size data from seabed shipek grab samples collected from R/V Ukpik in summer 2021 as part of NSF project 1913195 (Arctic Shelf sediment fate – an observational and modeling study of sediment pathways and morphodynamic feedbacks in a changing polar environment). Samples were collected from across Harrison Bay on the Alaskan Beaufort Shelf, north of the Colville River and between Oliktok Point and Cape Halkett. Samples were bagged in the field and returned to the University of North Carolina at Chapel Hill where grain-size analyses were performed using an Escitec Bettersizer S3Plus laser diffraction sensor. Samples were sonicated for two minutes prior to analyses. Samples ranged from well sorted sands (typically medium sand or fine) to poorly sorted bimodal sands and muds to unimodal muds. In the field, samples exhibited diverse textures including mud clasts and very stiff muds.