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A precise knowledge of landfast sea-ice (fast-ice) thickness is relevant to many different disciplines. Sea Ice Monitoring Stations (SIMS) are used to measure time series of fast-ice thickness at a location. SIMS measure ice and ocean temperature via thermistor strings with many different methods for extracting sea-ice thickness from temperature existing. This study investigates: if thickness results from temperature recorded by SIMS of different designs, and analysed with different methods are comparable; which methods are recommended for their robustness, precision and accuracy and how they compare to independent thickness measurements; how otherwise unuseable data can be salvaged through specific SIMS designs. We present an analysis of fast-ice thickness calculated from SIMS deployed in McMurdo Sound, Antarctica and in the Chukchi Sea near Utqiaġvik, Alaska, over two decades. We find that median thicknesses derived by different methods agree within 1 ± 1.5 cm for McMurdo Sound and 2 ± 3 cm for Utqiaġvik. Thus, it is possible to confidently compare data collected from different stations and analysed with different methods. The vertical gradient of sea-ice temperature gives the best results for fast-ice thickness during the growth season and including standard resistors in a thermistor string can reduce potential data loss due to noise.

The Resistance-Nodulation-Division (RND) efflux pump superfamily is pervasive among Gram-negative pathogens and contributes extensively to clinical antibiotic resistance. The opportunistic pathogenPseudomonas aeruginosacontains 12 RND-type efflux systems, with four contributing to resistance including MexXY-OprM which is uniquely able to export aminoglycosides. At the site of initial substrate recognition, small molecule probes of the inner membrane transporter (e.g., MexY) have potential as important functional tools to understand substrate selectivity and a foundation for developing adjuvant efflux pump inhibitors (EPIs). Here, we optimized the scaffold of berberine, a known but weak MexY EPI, using anin-silicohigh-throughput screen to identify berberine dimers with enhanced synergistic action with aminoglycosides. Further, docking and molecular dynamics simulations of berberine dimers reveal unique contact residues and thus sensitivities of MexY from distinctP. aeruginosastrains. This work thereby reveals berberine dimers to be useful probes of MexY transporter function and potential leads for EPI development.

We investigate the application of ground-based radar interferometry for measuring flexural-gravity waves in sea ice. We deployed a Gamma Portable Radar Interferometer (GPRI) on top of a grounded iceberg surrounded by landfast sea ice near Utqiaġvik, Alaska. The GPRI collected 238 acquisitions in stare-mode during a period of moderate lateral ice motion during 23–24 Apr 2021. Individual 30-second interferograms exhibit ~20–50 s periodic motion indicative of propagating infragravity waves with ~1 mm amplitudes. Results include examples of onshore wave propagation at the speed predicted by the water depth and a possible edge wave along an ice discontinuity. Findings are supported through comparison with on-ice Ice Wave Rider (IWR) accelerometers and modeled wave propagation. These results suggest that the GPRI can be a valuable tool to track wave propagation through sea ice and possibly detect changes in such properties across variable ice conditions.

Quaternary ammonium compounds (QACs) comprise a large class of surfactants, consumer products, and disinfectants. The recently-isolated QAC natural product tricepyridinium bromide displays potent inhibitory activity against S. aureus but due to its unique structure, its mechanism of action remains unclear. A concise synthetic route to access tricepyridinium analogs was thus designed and four N-alkyl compounds were generated in addition to the natural product. Biological analysis of these compounds revealed that they display remarkable selectivity towards clinically-relevant Gram-positive bacteria exceeding that of commercially-available QACs such as cetylpyridinium chloride (CPC) and benzalkonium chloride (BAC) while having little to no hemolytic activity. Molecular modeling studies revealed that tricepyridinium and shorter-chain N-alkyl analogs may preferentially bind to the QacR transcription factor leading to potential activation of the QAC resistance pathway found in MRSA; however, our newly synthesized analogs are able to overcome this liability.

The Polar Sea Ice Topography REconstruction System, or PSITRES, is a 3D camera system designed to continuously monitor an area of ice and water adjacent to an ice-going vessel. Camera systems aboard ships in the polar regions are common; however, the application of computer vision techniques to extract high-level information from the imagery is infrequent. Many of the existing systems are built for human involvement throughout the process and lack automation necessary for round the clock use. The PSITRES was designed with computer vision in mind. It can capture images continuously for days on end with limited oversight. We have applied the system in different ice observing scenarios. The PSITRES was deployed on three research expeditions in the Arctic and Subarctic, and we present applications in measuring ice concentration, melt pond fraction and presence of algae. Systems like PSITRES and the computer vision algorithms applied represent steps toward automatically observing, evaluating and analyzing ice and the environment around ships in ice-covered waters.

Variability in sea ice conditions, combined with strong couplings to the atmosphere and the ocean, lead to a broad range of complex sea ice dynamics. More in-situ measurements are needed to better identify the phenomena and mechanisms that govern sea ice growth, drift, and breakup. To this end, we have gathered a dataset of in-situ observations of sea ice drift and waves in ice. A total of 15 deployments were performed over a period of 5 years in both the Arctic and Antarctic, involving 72 instruments. These provide both GPS drift tracks, and measurements of waves in ice. The data can, in turn, be used for tuning sea ice drift models, investigating waves damping by sea ice, and helping calibrate other sea ice measurement techniques, such as satellite based observations.

Improving situational awareness and crisis response are key priorities in reducing potential risks associated with sea ice and environmental-related hazards in the Arctic. This research explores th...

Arctic sea ice incorporates and transports sediment, releasing it back into the water column during the melting season. This process constitutes an important aspect of marine sediment transport and biogeochemical cycling. Sediment incorporation into sea ice is considered to occur mainly through underwater interaction between frazil ice and resuspended sediment, referred to as suspension freezing. However, harsh environmental conditions have greatly limited field observations of this phenomenon. Analysis of mooring data from a coastal polynya in the northeastern Chukchi Sea, in conjunction with coastal ice radar and meteorological data, indicates that suspension freezing is a key mechanism for sediment entrainment into sea ice. During polynya episodes, acoustic backscatter data obtained by an Acoustic Doppler Current Profiler showed the presence of frazil ice from the surface down to 20- to 25-m depth, coinciding with in situ and potential supercooling. Underwater frazil ice persisted over 1 week under windy, turbulent water column conditions. A combination of the turbidity and Acoustic Doppler Current Profiler backscatter data revealed upward sediment dispersion associated with strong currents during the polynya episodes. The fact that frazil ice and resuspended sediment were detected at the same depth and time strongly suggests the interaction between ice crystals and sediment particles, that is, suspension freezing. Plain Language Summary Sea ice incorporates, transports, and releases particulate matter. These processes constitute an important aspect of the biology, biogeochemical cycling, and pollutant transport in polar oceans. Seafloor sediments serve as the most important source of such particulate matter; however, the process of sediment incorporation into sea ice remains poorly explored. We conducted a year-long study of sediment resuspension and entrainment processes, using underwater sensors deployed in the Chukchi Sea. During winter, wind-driven offshore transport of sea ice created area of open water and newly grown thin ice that persisted for several days, so-called coastal polynya or flaw lead system. Our sensors recorded small ice crystals, so-called frazil ice, that formed in the water column when water temperatures were below freezing point (supercooling). During some of these episodes, sediment was resuspended from the seafloor and dispersed upward by the strong currents, bringing it into water depths at which frazil ice was encountered. Such conditions provide for opportunities that allow frazil ice crystals or aggregates to capture resuspended sediment, a process referred to as suspension freezing. Based on this study, we propose that suspension freezing commonly occurs in shallow Arctic polynyas, serving as a key process of sediment incorporation into sea ice.

We combine Eulerian ice draft observations from moored ice-profiling sonars with buoy- and satellite-derived ice drift data to obtain Lagrangian observations of changes in the thickness distribution of sea ice circulating the Beaufort Sea. We examine repeat measurements of ice draft by identifying events where buoys or pseudobuoys made repeat overpasses within 30 km of ice-profiling sonar-equipped Beaufort Gyre Exploration Project moorings. Comparison of ice draft distributions from each overpass indicates that summertime melt rates are related to drift track, with more melt occurring in the southern Beaufort Sea than to the north. Additionally, we find that ice surviving summer in the Beaufort Sea since 2007 is similar in thickness to surrounding first-year sea ice by the end of the following winter. These findings are supported by continuous ice thickness data from ice mass balance buoys. By examining "plumes" of pseudobuoys originating at each mooring location, we identify anomalous northward transport of ice in the southern Beaufort Sea in 2007 that likely contributed to the record-breaking reduction in sea ice extent that year. We also find that repeat overpasses have been much rarer since 2007, due to reduced summertime sea ice extent in the Beaufort Gyre and possible changes in ice drift patterns. These changes contribute to diminished replenishment of multiyear sea ice volume in the Arctic. Plain Language Summary Using ice motion data from buoys and satellites, we track sea ice as it circulates in the Beaufort Gyre and measure changes in its thickness as it passes over moored upward looking sonars. Our results show that ice drifting through the southern Beaufort Sea in summer experiences significant thinning and that multiyear ice surviving the summer does not grow much thicker than first-year ice even after multiple winters. We also find that the northward retreat of the summertime ice edge in Beaufort Sea is leading to a reduced likelihood of ice recirculating and growing older and thicker in the Beaufort Gyre. Together, these changes make any recovery of the Arctic ice pack increasingly unlikely.

The sub-ice platelet layer (SIPL) is a highly porous, isothermal, friable layer of ice crystals and saltwater, that can develop to several meters in thickness under consolidated sea ice near Antarctic ice shelves. While the SIPL has been comprehensively described, details of its physics are rather poorly understood. In this contribution we describe the halo-thermodynamic mechanisms driving the development and stability of the SIPL in mushy-layer sea ice model simulations, forced by thermal atmospheric and oceanic conditions in McMurdo Sound, Ross Sea, Antarctica. The novelty of these simulations is that they predict a realistic model analogue for the SIPL. Two aspects of the model are essential: (a) a large initial brine fraction is imposed on newly forming ice, and (b) brine rejection via advective desalination. The SIPL appears once conductive heat fluxes become insufficient to remove latent heat required to freeze the highly porous new ice. Favorable conditions for SIPL formation include cold air, supercooled waters, and consolidated ice and snow that are thick enough to provide sufficient thermal insulation. Thermohaline properties resulting from large liquid fractions stabilize the SIPL, in particular a low thermal diffusivity. Intense convection within the isothermal SIPL generates the SIPL-consolidated ice contrast without transporting heat. Using standard physical constants and free parameters, the model successfully predicts the SIPL and consolidated ice thicknesses at six locations. While most simulations were performed with 50 layers, an SIPL emerged with moderate accuracy in thickness for three layers proving a low-cost representation of the SIPL in large-scale climate models.

We developed and deployed two inertial measurement units on mobile pack ice during a U.S. Navy drifting ice campaign in the Beaufort Sea. The ice camp was more than 1000 km from the nearest open water. The sensors were stationed on thick (&gt, 1 m) first- and multi–year ice to record 3-D accelerations at 10 Hz for one week during March 2020. During this time, gale-force winds exceeded 21 m per second for several hours during two separate wind events and reached a maximum of 25 m per second. Our observations show similar sets of wave bands were excited during both wind events. One band was centered on a period of ~14 s. Another band arrived several hours later and was centered on ~3.5-s. We find that the observed wave bands match a model dispersion curve for flexural gravity waves in ~1.2-m ice with a Young’s modulus of 3.5 GPa under compressive stresses of ~0.3 MPa. We further evaluate the bending stress and load cycles of the individual wave bands and their potential role in break-up of sea ice. This work demonstrates how observations of waves in sea ice using these and similar sensors can potentially be a valuable field-based tool for evaluating ice mechanics. In particular, this approach can be used to observe and describe the combined mechanical behavior of consolidated floes relevant for understanding sea ice mechanical processes and model development.

Arctic sea ice has retreated significantly over recent years. This ongoing sea ice decline has major implications for Arctic warming which motivates efforts to improve modeling capabilities. Human activities are also affected as sea ice is becoming less stable making ice roads, on-ice operations, and subsistence activities challenging in certain regions. To enhance modelling capabilities, ice use, and safety near sea ice, it is crucial to understand how sea ice deforms and fractures on the km-scale. Satellite remote sensing provides important insight into the mechanisms of large-scale sea ice deformation. However, analysis is frequently hampered by suboptimal data availability and lacks the spatiotemporal resolution necessary to resolve key processes.We examine ground-based radar interferometry as a tool to bridge the gap between spaceborne remote sensing and sea ice lab and in-situ measurements during two field campaigns. We deployed a Gamma portable radar interferometer (GPRI) during a drifting ice camp in the Beaufort Sea during spring 2020. Based on this data, we demonstrate the ability to derive km-scale 2-dimensional strain/stress fields through inverse modeling. This analysis also highlights the ability to resolve mm-scale variations in dynamic behavior between different ice regimes. We also deployed a GPRI at a fixed reference point on shore in Utqiaġvik, Alaska. This enabled the tracking of absolute motion over several hours revealing near uni-axial elastic divergence in response to offshore wind.Our analysis included efforts to remove signals from continuous antenna tilt due to ice motion when stationed on ice. We also needed to take steps to remove atmospheric phase contributions from the data obtained in Utqiaġvik during late spring. Overall, ground-based radar interferometry shows promise as a tool to track mm-scale sea ice dynamics. This may enable new insight into rheological behavior of sea ice and potentially the monitoring of dynamic precursors to fracture, which may improve safety near ice operations.

The inaugural data from the first systematic program of sea-ice observations in Kotzebue Sound, Alaska, in 2018 coincided with the first winter in living memory when the Sound was not choked with ice. The following winter of 2018–19 was even warmer and characterized by even less ice. Here we discuss the mass balance of landfast ice near Kotzebue (Qikiqtaġruk) during these two anomalously warm winters. We use in situ observations and a 1-D thermodynamic model to address three research questions developed in partnership with an Indigenous Advisory Council. In doing so, we improve our understanding of connections between landfast ice mass balance, marine mammals and subsistence hunting. Specifically, we show: (i) ice growth stopped unusually early due to strong vertical ocean heat flux, which also likely contributed to early start to bearded seal hunting; (ii) unusually thin ice contributed to widespread surface flooding. The associated snow ice formation partly offset the reduced ice growth, but the flooding likely had a negative impact on ringed seal habitat; (iii) sea ice near Kotzebue during the winters of 2017–18 and 2018–19 was likely the thinnest since at least 1945, driven by a combination of warm air temperatures and a persistent ocean heat flux.

Profound sea ice loss is rapidly transforming coupled social-ecological Arctic marine systems. However, explicit impacts to harvesting of traditional resources for coastal Indigenous communities remain largely unquantified, particularly where the primary research questions are posed by the Indigenous community as a result of emerging approaches such as knowledge co-production. Here, we directly link reduced sea ice coverage to decreasing harvesting opportunities for ugruk (bearded seal, Erignathus barbatus) as a component of a partnership among a multidisciplinary team of scientists, Indigenous Elder Advisory Council, and sovereign Indigenous tribe in northwest Alaska, USA. We collaboratively established research questions, coordinated data collection, and interpreted results to understand the causes and consequences of changing ugruk harvests for the community of Qikiqtaġruk (Kotzebue). The duration of spring ugruk hunts by the Qikiqtaġruŋmiut declined significantly during 2003–2019 due to a shift (∼3 weeks earlier) in the timing of regional sea ice breakup. Harvests now cease ∼26 d earlier than in the past decade. Using historical sea ice records, we further demonstrate that ice coverage in May now resembles conditions that were common in July during the mid-20th century. Overall, we show that climate change is constraining hunting opportunities for this traditional marine resource, although Qikiqtaġruŋmiut hunters have so far been able to offset a shortened season with changes in effort. Notwithstanding recent hunting success in unprecedentedly sparse ice conditions, accessibility to traditional resources remains a prominent concern for many Arctic communities. Management and policy decisions related to Arctic marine mammal resources, such as ugruk, are therefore also interwoven with food security, well-being, and culture of Indigenous communities. Hence, research that originates with Indigenous sovereignty over the entire research process, such as demonstrated here, has the potential to also lead to more inclusive, sustainable, and equitable outcomes in the face of rapid and accelerating Arctic change.

During the winter of 2016, anomalous sea ice conditions and a powerful storm culminated in a destructive erosion event along the Chukchi Sea coastline of Cape Espenberg, Alaska. This event is commonly referred to as an “ice push” or “ivu,” the Inupiat word for an ice ridging event. In this article, we report the process and impact of this event by combining traditional ecological knowledge, news accounts, meteorological data, remote sensing, and ground surveys. The midwinter detachment of shorefast ice was caused by a low-pressure system and wind-driven swell that destabilized shorefast ice, while northerly winds developed an open-water lead offshore to the eventual impact area. These conditions preceded the impact of an extratropical cyclone on December 31, 2016, when powerful southerly winds and the second largest storm surge in Kotzebue Sound since at least 2003 led to the compressional failure of the ice cover under uniaxial loading perpendicular to the southern coastline of the Cape, resulting in the ice push event. Ice-pushed debris was shoved up to 6.2 m above mean high water, with ∼3.5 km of coastline experiencing net erosion. The largest accumulation of ice-pushed debris had a volume of 1,000 m3, and rose 3 + m above the surrounding ground surface even after roughly 6 months of melting. On low-lying areas, driftwood and other debris were deposited 130 m landward by the surge 5.0 m above mean high water, indicating the potential threat of such events to property, infrastructure, and, in this case, archeological sites and associated cultural resources. The anomalous environmental and sea ice conditions that preceded the ivu seem to suggest that such events may occur more frequently in a warmer Arctic.

Arctic landfast sea ice has undergone substantial changes in recent decades, affecting ice stability and including potential impacts on ice travel by coastal populations and on industry ice roads. We present a novel approach for evaluating landfast sea ice stability on a pan-Arctic scale using Synthetic Aperture Radar Interferometry (InSAR). Using Sentinel-1 images from spring 2017, we discriminate between bottomfast, stabilized, and nonstabilized landfast ice over the main marginal seas of the Arctic Ocean (Beaufort, Chukchi, East Siberian, Laptev, and Kara seas). This approach draws on the evaluation of relative changes in interferometric fringe patterns. This first comprehensive assessment of Arctic bottomfast sea ice extent has revealed that most of the bottomfast sea ice is situated around river mouths and coastal shallows. The Laptev and East Siberian seas dominate the aerial extent, covering roughly 4100 and 5100 km2, respectively. These seas also contain the largest extent of stabilized and nonstabilized landfast ice, but are subject to the largest uncertainties surrounding the mapping scheme. Even so, we demonstrate the potential for using InSAR for assessing the stability of landfast ice in several key regions around the Arctic, providing a new understanding of how stability may vary between regions. InSAR-derived stability may serve for strategic planning and tactical decision support for different uses of coastal ice. In a case study of the Nares Strait, we demonstrate that interferograms may reveal early-warning signals for the breakup of stationary sea ice.

Water properties and formation processes of Alaskan Coastal Winter Water (ACWW) over the eastern Chukchi shelf along the Alaska coast, the so-called Barrow Canyon pathway, are examined using data from moorings, atmospheric reanalysis, satellite-derived sea-ice production (SIP), and a numerical tracer experiment. Along this pathway, Pacific Winter Water (PWW) can be modified to produce ACWW through SIP accompanied by production of cold, saline polynya water in the coastal polynyas, upwelling of warm Atlantic Water (AW), and mixing processes on the shelf. Three different types of ACWW are formed: (i) a mixture of AW and PWW, (ii) a mixture of AW and polynya water, and (iii) hypersaline polynya water. The northeasterly winds, correlated with the north-south atmospheric pressure gradient between Beaufort High and Aleutian Low, are common triggers of polynya SIP episodes and AW upwelling in the Barrow Coastal Polynya (BCP). Due to the dual impact of northeasterly winds, PWW modification processes in the BCP are more complicated than what occurs elsewhere in the Chukchi Polynya. The impact of AW upwelling on the ACWW formation is most prominent in the BCP, usually centered along the coast. All types of ACWW are thought to be basically transported westward or northwestward with the Chukchi slope current and/or Beaufort Gyre and finally contribute to maintenance of the lower halocline layer especially over the Chukchi Borderland, Northwind Ridge, and southern Canada Basin. Even in the Pacific sector of the Arctic Ocean, ACWW properties are strongly influenced by both Atlantic-origin and Pacific-origin waters.

Using thresholds of physical climate variables developed from community observations, together with two large-scale datasets, we have produced local indices directly relevant to the impacts of a reduced sea ice cover on Alaska coastal communities. The indices include the number of false freeze-ups defined by transient exceedances of ice concentration prior to a corresponding exceedance that persists, false break-ups, timing of freeze-up and break-up, length of the open water duration, number of days when the winds preclude hunting via boat (wind speed threshold exceedances), the number of wind events conducive to geomorphological work or damage to infrastructure from ocean waves, and the number of these wind events with on- and along-shore components promoting water setup along the coastline. We demonstrate how community observations can inform use of large-scale datasets to derive these locally relevant indices. The two primary large-scale datasets are the Historical Sea Ice Atlas for Alaska and the atmospheric output from a regional climate model used to downscale the ERA-Interim atmospheric reanalysis. We illustrate the variability and trends of these indices by application to the rural Alaska communities of Kotzebue, Shishmaref, and Utqiaġvik (previously Barrow), although the same procedure and metrics can be applied to other coastal communities. Over the 1979–2014 time period, there has been a marked increase in the number of combined false freeze-ups and false break-ups as well as the number of days too windy for hunting via boat for all three communities, especially Utqiaġvik. At Utqiaġvik, there has been an approximate tripling of the number of wind events conducive to coastline erosion from 1979 to 2014. We have also found a delay in freeze-up and earlier break-up, leading to a lengthened open water period for all of the communities examined.

Recent Arctic warming has led to reduced sea-ice thickness and a more dynamic landfast ice cover with potential widespread consequences for ice users. Here, we develop an approach to assess the small-scale deformation of landfast ice critical to on-ice operations using synthetic aperture radar interferometry (InSAR). InSAR has previously proven successful in determining long-term qualitative climatology of ice deformation around on-ice operations, but is now used to explore its potential for providing quantitative guidance for ice road planning, construction, and maintenance. A validation effort using X-band SAR and high-precision GPS data over Elson Lagoon, Alaska, confirms the ability of InSAR to accurately estimate 3-dimensional sea ice strain values accumulated between SAR image acquisitions, using an inverse model. The inverse model was further applied to L-band InSAR data over the Northstar Island ice road near Prudhoe Bay, Alaska. Assuming an elasto-brittle rheology, the derived strain values yielded a spatial distribution of internal stress consistent with preexisting ice defects and morphology. In several localized regions of the study area, stress values exceeded expected yield stress. Resulting relative fracture intensity potential was shown to conform with local knowledge based on road inspections by engineers, and may be used to guide ice road planning, construction and maintenance efforts. The results presented here demonstrate that InSAR is an accurate tool for estimating landfast ice deformation and stability in support of ice use. The findings may also provide substantial new insights into the mechanics of landfast ice.

Four (3,4-diphenylcyclopentadienone)iron tricarbonyl compounds were synthesized, and their activities in transfer hydrogenations of carbonyl compounds and transfer dehydrogenations of alcohols were explored and compared to those of the well-established [2,5-(SiMe3)2-3,4-(CH2)4(η4-C4C═O)]Fe(CO)3 (3). A new compound, [2,5-bis(3,5-dimethylphenyl)-3,4-diphenylcyclopentadienone]iron tricarbonyl (7), was the most active catalyst in both transfer hydrogenations and dehydrogenations, and compound 3 was the least active catalyst in transfer hydrogenations. Evidence was found for product inhibition of both 3 and 7 in a transfer dehydrogenation reaction, with the activity of 3 being more heavily affected. A monomeric iron hydride derived from 7 was spectroscopically observed during a transfer hydrogenation, and no diiron bridging hydrides were found under reductive or oxidative conditions. Initial results in the transfer hydrogenation of N-benzylideneaniline showed that 3 was a significantly less active catalyst in ...

Arctic landfast sea ice is widely utilized for transportation by local communities and industry, with trafficability largely governed by ice roughness. Here, we introduce an approach to evaluate ice roughness that can aid in routing of ice roads and assessment of spatial variability and long-term changes in trafficability. Drawing on synthetic aperture radar (SAR) polarimetry, SAR interferometry (InSAR), and other remote sensing techniques, we integrated approaches into the trafficability assessment that had rarely been applied over sea ice in the past. Analysis of aerial photogrammetry obtained through structure-from-motion helped verify cm-scale accuracy of X-band InSAR-derived ridge height and link L-band polarimetric classification to specific roughness regimes. Jointly, these approaches enable a km-scale evaluation of ridge topography and cm- to m-scale roughness—both critical for the assessment of trafficability. A trafficability index was derived from such SAR data in conjunction with analysis of ice trail routing and ice use near Utqiaġvik, Alaska. The index identifies areas of reduced trafficability, associated with pressure ridges or rubble ice, and served to delineate favorable trail routes for different modes of transportation, with potential uses ranging from ice road routing to emergency evacuation. Community outreach is needed to explore how this approach could assist different ice users in reducing risk, minimizing trail or ice construction efforts, and improving safety.

Moorings, hydrography, satellite-tracked drifters, and high-frequency radar data describe the annual cycle in circulation and water properties in the landfast ice zone (LIZ) of the Alaskan Beaufort Sea. Three seasons, whose duration and characteristics are controlled by landfast ice formation and ablation, define the LIZ: “winter”, “break-up”, and “open-water”. Winter begins in October with ice formation and ends in June when rivers commence discharging. Winter LIZ ice velocities are zero, under-ice currents are weak ( ~ 5 cm s−1), and poorly correlated with winds and local sea level. The along-shore momentum balance is between along-shore pressure gradients and bottom and ice-ocean friction. Currents at the landfast ice-edge are swift (~35 cm s−1), wind-driven, with large horizontal shears, and potentially unstable. Weak cross-shore velocities (~1 cm s−1) imply limited exchanges between the LIZ and the outer shelf in winter. The month-long break-up season (June) begins with the spring freshet and concludes when landfast ice detaches from the bottom. Cross-shore currents increase, and the LIZ hosts shallow (~2 m), strongly-stratified, buoyant and sediment-laden, under-ice river plumes that overlie a sharp, ~1 m thick, pycnocline across which salinity increases by ~30. The plume salt balance is between entrainment and cross-shore advection. Break-up is followed by the 3-month long open-water season when currents are swift (≥20 cm s−1) and predominantly wind-driven. Winter water properties are initialized by fall advection and evolve slowly due to salt rejection from ice. Fall waters and ice within the LIZ derive from local rivers, the Mackenzie and/or Chukchi shelves, and the Arctic basin.