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Among polar bears (Ursus maritimus), only parturient females den for extended periods, emerging from maternal dens in spring after having substantially depleted their energy reserves during a fast that can exceed 8 months. Although den emergence coincides with a period of increasing prey availability, polar bears typically do not depart immediately to hunt, but instead remain at the den for up to a month. This delay suggests that there are likely adaptive advantages to remaining at the den between emergence and departure, but the influence of the timing and duration of this post-emergence period on cub survival has not been evaluated previously. We used temperature and location data from 70 denning bears collared within the Southern Beaufort Sea and Chukchi Sea subpopulations to estimate the phenology of the post-emergence period. We evaluated the influence of various spatial and temporal features on duration of the post-emergence period and evaluated the potential influence of post-emergence duration on litter survival early in the spring following denning. For dens that likely contained viable cubs at emergence (n = 56), mean den emergence occurred on 16 March (SE = 1.4 days) and mean departure on 24 March (SE = 1.6 days), with dates typically occurring later in the Chukchi Sea relative to Southern Beaufort Sea and on land relative to sea ice. Mean duration of the post-emergence period was 7.9 days (SE = 1.4) for bears that were observed with cubs later in the spring, which was over 4 times longer than duration of those observed without cubs (1.9 days). Litter survival in the spring following denning (n = 31 dens) increased from 0.5 to 0.9 when duration of the post-emergence period increased by ~4 days and other variables were held at mean values. Our limited sample size and inability to verify cub presence at emergence suggests that future research is merited to improve our understanding of this relationship. Nonetheless, our results highlight the importance of the post-emergence period in contributing to reproductive success and can assist managers in developing conservation and mitigation strategies in denning areas, which will be increasingly important as human activities expand in the Arctic. [ABSTRACT FROM AUTHOR]

In Alaska's coastal environment, accurate information of sea ice conditions is desired by operational forecasters, emergency managers, and responders. Complicated interactions among atmosphere, waves, ocean circulation, and sea ice collectively impact the ice conditions, intensity of storm surges, and flooding, making accurate predictions challenging. A collaborative work to build the Alaska Coastal Ocean Forecast System established an integrated storm surge, wave, and sea ice model system for the coasts of Alaska, where the verified model components are linked using the Earth System Modeling Framework and the National Unified Operational Prediction Capability. We present the verification of the sea ice model component based on the Los Alamos Sea Ice Model, version 6. The regional, high-resolution (3 km) configuration of the model was forced by operational atmospheric and ocean model outputs. Extensive numerical experiments were conducted from December 2018 to August 2020 to verify the model's capability to represent detailed nearshore and offshore sea ice behavior, including landfast ice, ice thickness, and evolution of air–ice drag coefficient. Comparisons of the hindcast simulations with the observations of ice extent presented the model's comparable performance with the Global Ocean Forecast System 3.1 (GOFS3.1). The model's skill in reproducing landfast ice area significantly outperformed GOFS3.1. Comparison of the modeled sea ice freeboard with the Ice, Cloud, and Land Elevation Satellite-2 product showed a mean bias of −4.6 cm. Daily 5-day forecast simulations for October 2020–August 2021 presented the model's promising performance for future implementation in the coupled model system. Significance Statement: Accurate sea ice information along Alaska's coasts is desired by the communities for preparedness of hazardous events, such as storm surges and flooding. However, such information, in particular predicted conditions, remains to be a gap. This study presents the verification of the state-of-art sea ice model for Alaska's coasts for future use in the more comprehensive coupled model system where ocean circulation, wave, and sea ice models are integrated. The model demonstrates comparable performance with the existing operational ocean–ice coupled model product in reproducing overall sea ice extent and significantly outperformed it in reproducing landfast ice cover. Comparison with the novel satellite product presented the model's ability to capture sea ice freeboard in the stable ice season. [ABSTRACT FROM AUTHOR]

The rapid loss of arctic sea ice is forcing a larger proportion of the Southern Beaufort Sea polar bear (Ursus maritimus) population to spend more time on land, increasing chances of negative interactions between people and bears. In the United States, the Marine Mammal Protection Act (MMPA) protects polar bears from incidental disturbance from human activities. For the remote and roadless areas of northern Alaska, USA, effective management of small aircraft activity is necessary to limit disturbance, but effects of overflights on polar bear behavior are largely unknown. During 2021 and 2022, we intentionally exposed polar bears (n = 115) to systematic aircraft activity (helicopter, fixed-wing) until we observed a disruption of behavior that qualified as a level B take response (e.g., abrupt change in activity or movement) under the MMPA. We used a Bayesian logistic regression to determine what factors influence and can be used to predict when a polar bear will exhibit a level B take response and estimate the probability of an aircraft eliciting a level B take response at different altitudes above the polar bear. Aircraft type, flight altitude, landscape (barrier islands vs. mainland), and bear behavior (active vs. inactive) upon initial aircraft encounter were all important predictors of take. Probability of take rapidly increased with a decrease in flight altitude starting at 450m for helicopter and 300m for fixed-wing aircraft. Active (e.g., standing, walking) polar bears on barrier-island landscapes were more likely to experience take than inactive (e.g., bedded) bears on mainland landscapes. Our findings can help with assessments and management plans by quantifying disturbance to polar bears from current and future human activity that involves aircraft use. [ABSTRACT FROM AUTHOR]

The article discusses the close relationship between the Yupik people of St. Lawrence Island, Alaska, and walruses. The Yupik have relied on walruses for food, materials, and cultural expression. However, the Pacific walrus population was severely depleted by whalers in the late 1800s, leading to starvation and hardship for the island's communities. Today, the changing environment and increased human activity pose a double threat to walruses and the Yupik way of life. Efforts are being made to protect walruses and sustain the knowledge and skills needed to continue relying on them. The article emphasizes the importance of respect for walruses and supporting the rights of Indigenous communities. [Extracted from the article]

Climate-induced northward advance of boreal forest is expected to lessen albedo, alter carbon stocks, and replace tundra, but where and when this advance will occur remains largely unknown. Using data from 19 sites across 22 degrees of longitude along the tree line of northern Alaska, we show a stronger temporal correlation of tree ring growth with open water uncovered by retreating Arctic sea ice than with air temperature. Spatially, our results suggest that tree growth, recruitment, and range expansion are causally linked to open water through associated warmer temperatures, deeper snowpacks, and improved nutrient availability. We apply a meta-analysis to 82 circumarctic sites, finding that proportionally more tree lines have advanced where proximal to ongoing sea ice loss. Taken together, these findings underpin how and where changing sea ice conditions facilitate high-latitude forest advance. [ABSTRACT FROM AUTHOR]

Observations collected during cold-season precipitation periods at Utquagvik, Alaska and at the multidisciplinary drifting observatory for the study of Arctic climate (MOSAiC) are used to statistically analyze the relations among the atmospheric water cycle parameters including the columnar supercooled liquid and ice amounts (expressed as liquid-water and ice-water paths, i.e., LWP and IWP), the integrated water vapor (IWV) and the near-surface snowfall rate. Data come from radar and radiometer-based retrievals and from optical precipitation sensors. While the correlation between snowfall rate and LWP is rather weak, correlation coefficients between radar-derived snowfall rate and IWP are high (~0.8), which is explained, in part, by the generally low LWP/IWP ratios during significant precipitation. Correlation coefficients between snowfall rate and IWV are moderate (~0.45). Correlations are generally weaker if snowfall is estimated by optical sensors, which is, in part, due to blowing snow. Correlation coefficients between near-surface temperature and snowfall rates are low (r < 0.3). The results from the Alaska and MOSAiC sites are generally similar. These results are not very sensitive to the amount of time averaging (e.g., 15 min averaging versus daily averages). Observationally based relations among the water cycle parameters are informative about atmospheric moisture conversion processes and can be used for model evaluations. [ABSTRACT FROM AUTHOR]

The mechanism for the paradox of global warming and successive cold winters in mid-latitudes remains controversial. In this study, the connection between Arctic sea ice (ASI) loss and frequent cold air outbreaks in eastern Continental United States (CONUS) is explored. Two distinct periods of high and low ASI (hereafter high- and low-ice phases) are identified for comparative study. It is demonstrated that cold air outbreaks occur more frequently during the low-ice phase compared to that during the high-ice phase. The polar vortex is weakened and shifted southward during the low-ice phase. Correspondingly, the spatial pattern of 500 hPa geopotential height (GPH), which represents the mid-tropospheric circulation, shows a clear negative Arctic Oscillation-like pattern in the low-ice phase. Specifically, positive GPH anomalies in the Arctic region with two centers, respectively located over Greenland and the Barents Sea, significantly weaken the low-pressure system centered around the Baffin Island, and enhance Ural blocking in the low-ice phase. Meanwhile, the high ridge extending from Alaska to the west coast of North America further intensifies, while the low trough over eastern CONUS deepens. As a result, the atmospheric circulation in North America becomes more conductive to frigid Arctic air outbreaks. It is concluded that the ASI loss contributes to more cold air outbreaks in winter in eastern CONUS through the polar vortex weakening with southward displacement of the polar vortex edge, which lead to the weakening of the meridional potential vorticity gradient between the Arctic and mid-latitude and thus are conducive to the strengthening and long-term maintenance of the blocking high. [ABSTRACT FROM AUTHOR]

In recent decades, Arctic summer sea ice extent (SIE) has shown a rapid decline overlaid with large interannual variations, both of which are influenced by geopotential height anomalies over Greenland (GL-high) and the central Arctic (CA-high). In this study, SIE along coastal Siberia (Sib-SIE) and Alaska (Ala-SIE) is found to account for about 65% and 21% of the Arctic SIE interannual variability, respectively. Variability in Ala-SIE is related to the GL-high, whereas variability in Sib-SIE is related to the CA-high. A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast, promoting ice—albedo feedback. A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation (DLR) along the Siberian coast. The years 2012 and 2020 with minimum recorded ASIE are used as examples. Compared to climatology, summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast, while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast. In 2012, the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation, amplifying ice-albedo feedback there; while in 2020, the opposite occurs with an increase in cloud cover along the Alaskan coast, resulting in a slight increase in sea ice there. Along the Siberian coast, increased DLR in 2020 plays a dominant role in sea ice loss, and increased cloud cover and water vapor both contribute to the increased DLR. [ABSTRACT FROM AUTHOR]

The westerly wind on the poleward side of the summer polar jet stream (PJS) over the Western Hemisphere has significantly weakened since the 1980s. A weak summer PJS causes warming surface temperatures and deficient precipitation over Alaska and western North America, favoring extreme wildfire events. This study investigates influences of Arctic sea ice loss on the summer PJS variability over the Western Hemisphere. Regression analysis first provides observational evidence that Arctic sea ice reduction is related to a weakening summer Western Hemisphere PJS at interannual time scales. Atmospheric model ensemble simulations are then used to demonstrate that Arctic sea ice loss significantly contributes to observed Western Hemisphere Arctic warming and reduced meridional temperature gradient between midlatitudes and the pole in the lower and middle troposphere, acting to weaken the troposphere zonal wind and vertical wind shear from 55° to 75°N, and about 20–30% of observed weakened summer PJS trend during 1979–2014. Observational analysis and the model-based results also indicate that a significant portion of the observed trends of the PJS and vertical wind shear during 1979–2014 might be attributed to the decadal variability of the summer North Atlantic Oscillation (NAO). In the future climate, as more and more ice melts in the summer, the weakening effect of sea ice on the PJS will continue and will be superimposed onto the natural decadal variability of the PJS. [ABSTRACT FROM AUTHOR]

The attenuation of ocean surface waves during seasonal ice cover is an important control on the evolution of Arctic coastlines. The spatial and temporal variations in this process have been challenging to resolve with conventional sampling using sparse arrays of moorings or buoys. We demonstrate a novel method for persistent observation of wave‐ice interactions using distributed acoustic sensing (DAS) along existing seafloor fiber optic telecommunications cables. DAS measurements span a 36‐km cross‐shore cable on the Beaufort Shelf from Oliktok Point, Alaska. DAS optical sensing of fiber strain‐rate provides a proxy for seafloor pressure, which we calibrate with wave buoy measurements during the ice‐free season (August 2022). We apply this calibration during the ice formation season (November 2021) to obtain unprecedented resolution of variable wave attenuation rates in new, partial ice cover. The location and strength of wave attenuation serve as proxies for ice coverage and thickness, especially during rapidly evolving events. Plain Language Summary: Coasts globally are susceptible to erosion by ocean waves. In the Arctic, sea ice near the coast can serve as protection for much of the year. It is particularly challenging to measure waves and ice in this environment, which is necessary to understand the degree of buffering and project future changes. Typical ways of observing waves (e.g., buoys and underwater moorings) have lower success in coastal ice. We show a new way to observe waves and ice in these coastal regions using cables at the seabed deployed for internet connection. With the use of an instrument called an interrogator on shore, fibers in these cables can act like a series of hundreds of wave buoys. This allows us to see that waves are reduced at a variable rate throughout the ice. There are significant opportunities to learn more about the coastal Arctic using this novel technology and method. Key Points: Seafloor fiber optic cables can be used to quantify surface waves in seasonally sea ice‐covered oceansHigh spatial‐resolution wave observations may be used to study wave attenuation in ice at much finer resolution than previously possibleThe rapid evolution of the location and strength of attenuation serves as proxy for the evolution of ice itself [ABSTRACT FROM AUTHOR]

Alaska is one of the most seismically active regions of the world. Coincidentally, the state has also experienced dramatic impacts of climate change as it is warming at twice the rate of the rest of the United States. Through mechanisms such as permafrost thaw, water table fluctuation, and melting of sea ice and glaciers, climatic-driven changes to the natural and built-environment influence the seismic response of infrastructure systems. This paper discusses the challenges and needs posed by earthquake hazards and climate change to Alaska's infrastructure and built environment, drawing on the contributions of researchers and decision-makers in interviews and a workshop. It outlines policy, mitigation, and adaptation areas meriting further attention to improve the seismic resilience of Alaska's built environment from the perspectives of engineering and complementary coupled human-environmental systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Throughout winter, the winds of migrating weather systems drive the recurrent opening of sea ice leads from Alaska's northernmost headland, Point Barrow. As leads extend offshore into the Beaufort and Chukchi seas, they produce sea ice velocity discontinuities that are challenging to represent in models. We investigate how synoptic wind patterns form leads originating from Point Barrow and influence patterns of sea ice drift across the Pacific Arctic. We identify 135 leads from satellite thermal infrared imagery between January–April 2000–2020 and generate an ensemble of lead-opening sequences by averaging atmospheric conditions and ice velocity across events. On average, leads open as migrating atmospheric highs drive differing ice–coast interactions across Point Barrow. Northerly winds compress the Beaufort ice pack against the coast over several days, slowing ice drift. As winds west of Point Barrow shift offshore, the ice cover fractures and a lead extends from the headland into the pack interior. Ice west of the lead accelerates as it separates from the coast, drifting twice as fast (relative to winds) as ice east of the lead, which remains coastally bound. Consequently, sea ice drift and its contribution to climatological ice circulation becomes zonally asymmetric across Point Barrow. These findings highlight how coastal boundaries modify the response of the consolidated ice pack to wind forcing in winter, producing spatially varying regimes of ice stress and kinematics. Observed connections between winds, ice drift, and lead opening provide test cases for sea ice models aiming to capture realistic ice transport during these recurrent deformation events. [ABSTRACT FROM AUTHOR]

Some of the largest climatic changes in the Arctic have been observed in Alaska and the surrounding marginal seas. Near-surface air temperature (T2m), precipitation (P), snowfall, and sea ice changes have been previously documented, often in disparate studies. Here, we provide an updated, long-term trend analysis (1957-2021; n 5 65 years) of such parameters in ERA5, NOAA U.S. Climate Gridded Dataset (NClimGrid), NOAA National Centers for Environmental Information (NCEI) Alaska climate division, and composite sea ice products preceding the upcoming Fifth National Climate Assessment (NCA5) and other near-future climate reports. In the past half century, annual T2m has broadly increased across Alaska, and during winter, spring, and autumn on the North Slope and North Panhandle (T2m. 0.508C decade21). Precipitation has also increased across climate divisions and appears strongly interrelated with temperature-sea ice feedbacks on theNorth Slope, specifically with increased (decreased) open water (sea ice extent). Snowfall equivalent (SFE) has decreased in autumn and spring, perhaps aligned with a regime transition of snow to rain, while winter SFE has broadly increased across the state. Sea ice decline and melt-season lengthening also have a pronounced signal around Alaska, with the largest trends in these parameters found in the Beaufort Sea. Alaska's climatic changes are also placed in context against regional and contiguous U.S. air temperature trends and show; 50% greater warming in Alaska relative to the lower-48 states. Alaska T2m increases also exceed those of any contiguous U.S. subregion, positioning Alaska at the forefront of U.S. climate warming. [ABSTRACT FROM AUTHOR]

The biogeochemical cycling of nitrogen (N) plays a critical role in supporting marine ecosystems and controlling primary production. Nitrification, the oxidation of ammonia (NH3) by microorganisms, is an important process in the marine N cycle, supplying nitrate (NO3−), the primary source of N that fuels new phytoplankton growth, and the primary substrate for the microbial process of denitrification. Understanding nitrification in the Chukchi Sea, the shallow sea overlying the continental shelf north of Alaska and the Bering Strait, is particularly important as phytoplankton growth there has been shown to be limited by N. However, the controls on nitrification in the water column and potential effects of climate change remain unknown. This study seeks to characterize the controls on nitrification in the Chukchi Sea. We found light to be a strong control on nitrification rates. Nitrification was undetectable at light levels above 23 μmol photons m−2 s−1. Subsequently, sea ice concentration was related to nitrification, with rates being higher at stations with high ice cover where light transmission to the water column was reduced. High ammonium (NH4+) concentrations also enhanced nitrification, suggesting that nitrifying organisms were substrate‐limited, likely due to competition for NH4+ from phytoplankton. Unlike previous experimental studies, we found that nitrification rates were higher under low pH conditions. As the effects of ocean acidification and warming disproportionately impact the Arctic, nitrification rates will undoubtedly be affected. Our results will help guide future studies on potential implications of climate change on the biogeochemistry of N in the Chukchi Sea. [ABSTRACT FROM AUTHOR]

In recent decades, the Arctic has warmed faster than the global mean, especially during winter. This has been attributed to various causes, with recent studies highlighting the importance of enhanced downward infrared radiation associated with anomalous inflow of warm, moist air from lower latitudes. Here, we study wintertime surface energy budget (SEB) anomalies over Arctic sea ice on synoptic time scales, using ERA5 (1979–2020). We introduce a new algorithm to identify areas with extreme, positive daily mean SEB anomalies and connect them to form spatiotemporal life cycle events. Most of these events are associated with large-scale inflow from the Atlantic and Pacific Oceans, driven by poleward deflection of the storm track and blocks over northern Eurasia and Alaska. Events originate near the ice edge, where they have roughly equal contributions of net longwave radiation and turbulent fluxes to the positive SEB anomaly. As the events move farther into the Arctic, SEB anomalies decrease due to weakening sensible and latent heat-flux anomalies, while the surface temperature anomaly increases toward the peak of the events along with the downward longwave radiation anomaly. Due to these temporal and spatial differences, the largest SEB anomalies are not always related to strongest surface warming. Thus, studying temperature anomalies alone might not be sufficient to determine sea ice changes. This study highlights the importance of turbulent fluxes in driving SEB anomalies and downward longwave radiation in determining local surface warming. Therefore, both processes need to be accurately represented in climate models. Significance Statement: Mechanisms behind wintertime rapid Arctic warming and sea ice growth changes are not well understood. While much is known about the impact of radiative fluxes on both sea ice variability and surface warming, the relative importance of radiative and turbulent fluxes remains unclear. The purpose of this study is to clarify what controls surface energy budget (SEB) anomalies over sea ice. Along the life cycle of synoptic-scale events, positive SEB anomalies are shown to decrease and surface temperature anomalies increase after their onset. Additionally, variations in SEB anomalies are primarily controlled by turbulent fluxes, while downward longwave radiative fluxes are mainly responsible for surface temperature variations. These results highlight the need for accurate representations of these fluxes for predicting future Arctic climate. [ABSTRACT FROM AUTHOR]

From 17 November to 27 December 2022, extremely cold snowstorms frequently swept across North America and Eurasia. Diagnostic analysis reveals that these extreme cold events were closely related to the establishment of blocking circulations. Alaska Blocking (AB) and subsequent Ural Blocking (UB) episodes are linked to the phase transition of the North Atlantic Oscillation (NAO) and represent the main atmospheric regimes in the Northern Hemisphere. The downstream dispersion and propagation of Rossby wave packets from Alaska to East Asia provide a large-scale connection between AB and UB episodes. Based on the nonlinear multi-scale interaction (NMI) model, we found that the meridional potential vorticity gradient (PVy) in November and December of 2022 was anomalously weak in the mid-high latitudes from North America to Eurasia and provided a favorable background for the prolonged maintenance of UB and AB events and the generation of associated severe extreme snowstorms. However, the difference in the UB in terms of its persistence, location, and strength between November and December is related to the positive (negative) NAO in November (December). During the La Niña winter of 2022, the UB and AB events are related to the downward propagation of stratospheric anomalies, in addition to contributions by La Niña and low Arctic sea ice concentrations as they pertain to reducing PVy in mid-latitudes. [ABSTRACT FROM AUTHOR]

Tundra shrubs reflect climate sensitivities in their growth-ring widths, yet tissue-specific shrub chronologies are poorly studied. Further, the relative importance of regional climate patterns that exert mesoscale precipitation and temperature influences on tundra shrub growth has been explored in only a few Arctic locations. Here, we investigate Betula nana growth-ring chronologies from adjacent dry heath and moist tussock tundra habitats in arctic Alaska in relation to local and regional climate. Mean shrub and five tissue-specific ring width chronologies were analyzed using serial sectioning of above- and below-ground shrub organs, resulting in 30 shrubs per site with 161 and 104 cross sections from dry and moist tundra, respectively. Betula nana growth-ring widths in both habitats were primarily related to June air temperature (1989–2014). The strongest relationships with air temperature were found for 'Branch2' chronologies (dry site: r = 0.78, June 16, DOY = 167; moist site: r = 0.75, June 9, DOY = 160). Additionally, below-ground chronologies ('Root' and 'Root2') from the moist site were positively correlated with daily mean air temperatures in the previous late-June ('Root2' chronology: r = 0.57, pDOY = 173). Most tissue-specific chronologies exhibited the strongest correlations with daily mean air temperature during the period between 8 and 20 June. Structural equation modeling indicated that shrub growth is indirectly linked to regional Arctic and Pacific Decadal Oscillation (AO and PDO) climate indices through their relation to summer sea ice extent and air temperature. Strong dependence of Betula nana growth on early growing season temperature indicates a highly coordinated allocation of resources to tissue growth, which might increase its competitive advantage over other shrub species under a rapidly changing Arctic climate. [ABSTRACT FROM AUTHOR]

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 April 2021. Individual 30 s 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. [ABSTRACT FROM AUTHOR]

Seismic instruments such as broadband seismometers and distributed acoustic sensors (DAS) have a demonstrated potential for wide‐scale and continuous in situ monitoring of near‐surface environmental and anthropogenic processes. DAS is attractive for development as a multi‐geophysical observatory due to the prevalence of existing fiber infrastructure in regions with environmental, cultural, or strategic significance. Here we present results from a multi‐seasonal acquisition of DAS data on a seafloor cable in the Beaufort Sea, Alaska. During a November 2021 data collect we captured the rapid transition of ambient noise characteristics from an "ice‐free" state to an "ice‐bound" state. A sea ice formation front was plainly visible on the DAS record and was observed to propagate 20 km seaward over a period of 8 hr. Satellite‐based instrumentation were unable to record this event due to cloud cover, low light conditions, and orbital frequency. Plain Language Summary: Distributed acoustic sensing (DAS) is an emerging technology that uses fiber optic cable to mimic a high resolution array of one dimensional seismometers. Distributed acoustic sensors is compatible with any single‐mode fiber optic cable, including seafloor telecommunications cables. Previous recordings of DAS data on seafloor cables have demonstrated that this technology is able to detect and track individual ocean waves, surface vessels, and whales. In this first‐ever acquisition of DAS data from a seafloor beneath a frozen ocean, we show that DAS is also capable of mapping sea ice coverage with unprecedented spatial resolution and can track sea ice formation and breakup up in near real time. Key Points: Seafloor distributed acoustic sensing can distinguish between sea ice and open water on the basis of endemic wave modesThis technology is capable of high resolution, near real time imaging of sea ice dynamics, such as rapid freezing of marginal iceThis can complement large scale, low resolution satellite‐based imaging in regions of high scientific or operational importance [ABSTRACT FROM AUTHOR]

Lakes in the Arctic are important reservoirs of heat with much lower albedo in summer and greater absorption of solar radiation than surrounding tundra vegetation. In the winter, lakes that do not freeze to their bed have a mean annual bed temperature >0 ∘ C in an otherwise frozen landscape. Under climate warming scenarios, we expect Arctic lakes to accelerate thawing of underlying permafrost due to warming water temperatures in the summer and winter. Previous studies of Arctic lakes have focused on ice cover and thickness, the ice decay process, catchment hydrology, lake water balance, and eddy covariance measurements, but little work has been done in the Arctic to model lake heat balance. We applied the LAKE 2.0 model to simulate water temperatures in three Arctic lakes in northern Alaska over several years and tested the sensitivity of the model to several perturbations of input meteorological variables (precipitation, shortwave radiation, and air temperature) and several model parameters (water vertical resolution, sediment vertical resolution, depth of soil column, and temporal resolution). The LAKE 2.0 model is a one-dimensional model that explicitly solves vertical profiles of water state variables on a grid. We used a combination of meteorological data from local and remote weather stations, as well as data derived from remote sensing, to drive the model. We validated modeled water temperatures with data of observed lake water temperatures at several depths over several years for each lake. Our validation of the LAKE 2.0 model is a necessary step toward modeling changes in Arctic lake ice regimes, lake heat balance, and thermal interactions with permafrost. The sensitivity analysis shows us that lake water temperature is not highly sensitive to small changes in air temperature or precipitation, while changes in shortwave radiation and large changes in precipitation produced larger effects. Snow depth and lake ice strongly affect water temperatures during the frozen season, which dominates the annual thermal regime of Arctic lakes. These findings suggest that reductions in lake ice thickness and duration could lead to more heat storage by lakes and enhanced permafrost degradation. [ABSTRACT FROM AUTHOR]

Widely recognized environmental changes have been negatively impacting communities in the Arctic for decades. The increased prevalence of open water in the Bering Sea during winter months, also known as sea ice loss, has uprooted annual traditional subsistence activities across the Bering Sea region. This article investigates the consequences of sea ice loss on traditional subsistence activities in Unalakleet, Alaska. In conjunction with the loss of sea ice over the past 30 years, the winter season in Unalakleet has shifted from cold and dry weather regimes to warmer and wetter winters. The change in winter weather and the increased prevalence of open water in winter has deeply impacted the people of Unalakleet by affecting environmental conditions and the availability of subsistence of resources, notably influencing winter and spring marine mammals hunts that people in the Unalakleet area have relied on for thousands of years. This article is guided by the perspectives, knowledge, and intuition of people from Unalakleet, and looks specifically at how the increased prevalence of open water in the Bering Sea during wintertime has impacted traditional subsistence rounds (the suc)cession of food resources through the seasons) in Unalakleet, Alaska, in 2022 [ABSTRACT FROM AUTHOR]

Ringed (Pusa hispida), bearded (Erignathus barbatus), spotted (Phoca largha), and ribbon seals (Histriophoca fasciata), or ice seals, are harvested for subsistence purposes by many Alaska Native communities. We address trends in the subsistence harvest of ice seals for the Yukon-Kuskokwim Delta region of Alaska for more than 50 years using two types of data collected by the Alaska Department of Fish and Game: (1) bounty data collected from 1962 to 1972 for 16 communities, and (2) household survey data collected for seven of these communities from 1997 to 2018. Both include information on the number of ice seals harvested by each community annually. In addition, more detailed household surveys were conducted from 2008 to 2018 for Hooper Bay, Tununak, and Quinhagak, which collected data on the number of seals harvested by species, the percentage of households engaged in hunting or using seal products, and hunter perceptions. For the bounty period, we identified several years where most communities had above or below average harvests, suggesting regional drivers contributed to patterns in the ice seal harvest. For the seven communities with household survey data, the mean total harvest estimate during the household survey years was only slightly lower than during the bounty period, however, the human population doubled during this time, resulting in a substantial decline in the mean number of seals harvested per person. The more detailed surveys for Hooper Bay, Tununak, and Quinhagak also showed declines in seal harvests during the most recent decade. The declining harvest in some communities may be driven by reduced participation in hunting and less use of seal products. Ongoing sea ice loss is also likely contributing to the decline in harvest across the region. Current seal population estimates indicate all four species are abundant in Alaskan waters, and most hunters have not observed changes in seal abundance. [ABSTRACT FROM AUTHOR]

Although polar bears (Ursus maritimus) of the Southern Beaufort Sea (SBS) subpopulation have commonly created maternal dens on sea ice in the past, maternal dens on land have become increasingly prevalent as sea ice declines. This trend creates conditions for increased human–bear interactions associated with local communities and industrial activity. Maternal denning is a vulnerable period in the polar bear life cycle, and den disturbance could lead to den abandonment, cub mortality, and negative population impacts. We used published long‐term data to parameterize a Bayesian hierarchical model of annual land den abundance during 2000–2015, in 4 regions of northern Alaska, USA, with current or potential future oil and gas activity. We also estimated long‐term (1982–2015) shifts in the spatial distribution of land dens within and among regions using kernel density estimation and assessed the influence of local and regional sea ice and snow conditions on den site selection using a random forest resource selection function. Our objectives were to quantify current den distribution and abundance, test for distributional shifts over time, and investigate if those shifts could be attributed to environmental variables related to den habitat. We estimated that between 2000 and 2015, the SBS contained a median 123 dens in a typical year, of which 68 occurred on land. The region between the Colville and Canning rivers, where most current oil and gas activity occurred, also contained the largest fraction of land dens. Overall, land dens were disproportionately concentrated on barrier islands and on land within 30 km of the coast. The probability of dens occurring on land varied from 1982–1999 to 2000–2015 in all regions, and the overall distribution of land dens shifted west between those periods. This regional‐scale change in den distribution was predictable based on spatial and temporal heterogeneity in snow and sea ice conditions within 50 km of individual den locations. Land denning is likely to become increasingly common with continued sea ice loss, and our results and modeling framework could be used to design additional mitigation strategies for reducing the risk of incidental take due to den disturbance. [ABSTRACT FROM AUTHOR]

Two decades (2000–2019) of the landfast ice properties in the Beaufort Sea region in the Canadian Arctic were analyzed at 250 m spatial resolution from two sources: (1) monthly maps derived at the Canada Centre for Remote Sensing from the Moderate Resolution Imaging Spectroradiometer clear-sky satellite image composites; and (2) Canadian Ice Service charts. Detailed comparisons have been conducted for the landfast ice spatial extent, the water depth at, and the distance to the outer seaward edge from the coast in four sub-regions: (1) Alaska coast; (2) Barter Island to Herschel Island; (3) Mackenzie Bay; and (4) Richards Island to Cape Bathurst. The results from both sources demonstrate good agreement. The average spatial extent for the entire region over the April–June period is 48.5 (±5.0) × 103 km2 from Canadian Ice Service data versus 45.1 (±6.1) × 103 km2 from satellite data used in this study (7.0% difference). The correlation coefficient for April–June is 0.73 (p = 2.91 × 10−4). The long-term linear trends of the April–June spatial extent since 2000 demonstrated statistically significant decline: −4.45 (±1.69) × 103 km2/decade and −4.73 (±2.17) × 103 km2/decade from Canadian Ice Service and satellite data, respectively. The landfast ice in the Beaufort Sea region showed the general tendency for an earlier break-up, later onset, and longer ice-free period. The break-up date has decreased by 7.6 days/decade in the Mackenzie Bay region. The western part of the study area did not demonstrate statistically significant changes since 2000. [ABSTRACT FROM AUTHOR]

Prompted by field observation of an aufeis‐induced channel avulsion along the Hula Hula River in June 2021, we use measurements of channel migration zone width along 15 rivers flowing north across the Arctic coastal plain in Alaska, USA. We differentiated sites with aufeis that covered ≥1 km2 in early summer during the period 2017–2021 from sites without such aufeis formation. All but four of the 28 sites with aufeis have widths greater than the 95% confidence interval and 20 sites fall outside of the 95% prediction interval for channel width based on drainage area. Pairwise comparison indicates that the population of aufeis sites have significantly wider channel migration zones (p < 0.0001) than non‐aufeis sites after accounting for drainage area. Seasonal aufeis facilitates lateral channel migration and associated heterogeneity. Loss of aufeis under warming climate may reduce habitat diversity in these river corridors. Plain Language Summary: Aufeis forms in Arctic river corridors when groundwater springs continue to provide water to the surface after the river is covered by ice. The resulting shelves of ice can be up to 3 m thick and extend across the channel and floodplain. As this ice slowly melts in early summer, it can divert river flow from the active channel onto the floodplain, creating new channels. This paper examines the resulting width of the floodplain across which active channel migration occurs. Comparing sites with and without aufeis, we find that sites with aufeis are significantly wider. Loss of aufeis with warming climate will reduce the habitat diversity of Arctic rivers. Key Points: Aufeis that persists into summer on rivers of the Alaskan Arctic coastal plain can force channel avulsionSites with repeated aufeis in successive years have wider channel migration zonesLoss of aufeis as climate warms may result in narrower and less diverse river corridors [ABSTRACT FROM AUTHOR]

There are multiple extreme events underway in the Arctic that are beyond previous records: rain in Greenland, Alaska weather variability, and ecosystem reorganizations in the Barents and the northern Bering Sea associated with climate change and sea-ice loss. Such unique extreme events represent a philosophical challenge for interpretation, i.e., a lack of statistical basis, as well as important information for regional adaptation to climate change. These changes are affecting regional food security, human/wildlife health, cultural activities, and marine wildlife conservation. Twenty years ago, the Arctic was more resilient to climate change than now, as sea ice had a broader extent and was three times thicker than today. These new states cannot be assigned probabilities because one cannot a priori conceive of these states. They often have no historical analogues. A way forward for adaptation to future extremes is through scenario/narrative approaches; a recent development in climate change policy is through decision making under deep uncertainty (DMDU). [ABSTRACT FROM AUTHOR]

Sea-ice pore microstructure constrains ice transport properties, affecting fluid flow relevant to oil-in-ice transport and biogeochemical processes. Motivated by a lack of pore microstructural data, in particular for granular ice and across the seasonal cycle, throat size, tortuosity, connectivity, and other microstructural variables were derived from X-ray computed tomography for brine-filled pores in seasonal landfast ice off northern Alaska. Data were obtained for granular and columnar ice during the ice growth, transition, and melt season. While granular ice exhibits a more heterogeneous pore space than columnar ice, pore and throat size distributions are comparable. The greater tortuosity of pores in granular (1.2 < τg < 1.7) compared to columnar ice (1.0 < τc < 1.1) compounded with a less interconnected pore space translates into lower permeability for granular ice during the growth season for a given porosity. The microstructural data explain findings of granular ice hindering vertical oil-in-ice transport during ice growth and transition stage. With granular ice more frequent in the changing Arctic, data from studies such as this are needed to inform improved modeling of porosity-permeability relationships. [ABSTRACT FROM AUTHOR]

Fjord circulation modulates the connection between marine‐terminating glaciers and the ocean currents offshore. These fjords exhibit both overturning and horizontal recirculations, which are driven by water mass transformation at the head of the fjord via subglacial discharge plumes and distributed meltwater plumes. However, little is known about how various fjord characteristics influence the interaction between 3D fjord circulation and glacial melt. In this study, high‐resolution numerical simulations of idealized glacial fjords demonstrate that recirculation strength controls melt, which feeds back on overturning and recirculation. The relationships between overturning, recirculation, and melt rate are well predicted by vorticity balance, reduced‐order melt parameterizations, and empirical scaling arguments. These theories allow us to take into account the near‐glacier horizontal velocities, which yield improved predictions of fjord overturning, recirculation, and glacial melt. Plain Language Summary: Glacial fjords are long, narrow, and deep inlets that connect glaciers to the open ocean. These glacial fjords exist around the margins of Greenland, West Antarctica, Alaska, and other regions, and collectively contribute a significant source of ice discharge into the ocean. Over the past two decades, tidewater glaciers in Greenland have accelerated, which can lead to sea level rise, and there is growing evidence that this acceleration is caused by deep warm water currents that flow into the fjords from the open ocean. These warm water currents have the potential to melt the submarine sides of glaciers, causing them to retreat over time. The dynamics of warm water delivery to the glacier face, particularly its interaction with fjord circulation, are presently poorly understood. In this study, we use high‐resolution, process‐oriented simulations to understand fjord currents and how they vary with different fjord characteristics and lead to different rates of submarine melting of the glacier face. We find that submarine glacial melt can cause feedbacks by amplifying the strength of the ocean currents, which further increase glacial melt. These results are an important step toward understanding a critical process that may help us improve sea level rise predictions. Key Points: Simulations show face‐wide glacial melt dominates the total melt due to its concentration at deeper depths versus discharge plume‐driven meltGlacial melt in fjords is primarily driven by recirculation at depth for most fjord properties, which is in turn driven by overturningFace‐wide glacial melt drives a significant warm‐water overturning and recirculation at depth, leading to a melt‐circulation feedback [ABSTRACT FROM AUTHOR]

This paper describes a remotely monitored buoy that, when deployed in open water prior to freeze up, permits scientists to monitor not only temperature with depth, and hence freeze up and sea ice thickness, but also the progression of sea ice development—e.g., the extent of cover at a given depth as it grows (solid fraction), the brine volume of the ice, and the salinity of the water just below, which is driven by brine expulsion. Microstructure and In situ Salinity and Temperature (MIST) buoys use sensor "ladders" that, in our prototypes, extend to 88 cm below the surface. We collected hourly measurements of surface air temperature and water temperature and electrical impedance every 3 cm to track the seasonal progression of sea ice growth in Elson Lagoon (Utqiaġvik, Alaska) over the 2017/18 ice growth season. The MIST buoy has the potential to collect detailed sea ice microstructural information over time and help scientists monitor all parts of the growth/melt cycle, including not only the freezing process but the effects of meteorological changes, changing snow cover, the interaction of meltwater, and drainage. Significance Statement: There is a need to better understand how an increasing influx of freshwater, one part of a changing Arctic climate, will affect the development of sea ice. Current instruments can provide information on the growth rate, extent, and thickness of sea ice, but not direct observations of the structure of the ice during freeze up, something that is tied to salinity and local air and water temperature. A first deployment in Elson Lagoon in Utqiaġvik, Alaska, showed promising results; we observed fluctuations in ice temperatures in response to brief warmings in air temperature that resulted in changes in the conductivity, liquid fraction, and brine volume fraction within the ice. [ABSTRACT FROM AUTHOR]

Human activities (e.g., shipping, tourism, oil, gas development) have increased in the Chukchi Sea because of declining sea ice. The declining sea ice itself and these activities may affect Pacific walrus (Odobenus rosmarus divergens) abundance; however, previous walrus abundance estimates have been notably imprecise. When sea ice is absent from the eastern Chukchi Sea, walruses in waters of the United States usually rest together onshore at a single Alaska coastal haulout, where they can be surveyed more easily than when they rest on dispersed offshore ice floes. We estimated the number of walruses on land (herd size) at this haulout from 13 unoccupied aircraft system (UAS) surveys flown within a 10‐day period in each of 2018 and 2019. We estimated population size of walruses using the haulout over the course of the surveys by combining herd size data with data from satellite‐linked transmitters that indicated whether tagged walruses were in or out of water during each survey. Our estimates of the population size of walruses using the haulout during each year's survey period were similar to each other and more precise than historical walrus abundance estimates: posterior means (95% credibility intervals) were 166,000 (133,000–201,000) for 2018 and 189,000 (135,000–251,000) for 2019. Auxiliary observations support using these estimates to represent the size of the population using the eastern Chukchi Sea in autumn during the surveyed years. Our study site was the only substantial Chukchi Sea coastal haulout in the United States during the survey periods and study‐specific tracking data (consistent with known distribution and movement patterns) indicated tagged walruses remained in eastern Chukchi waters during the survey periods. In addition, the imagery, telemetry, and analytical methods developed for this study advance the prospect for precise range‐wide walrus population size estimates. [ABSTRACT FROM AUTHOR]

The Northwest Coast of North America stretches 4000 km from Bering Strait to Washington State. Here we review the history of glaciation, sea level, oceanography, and climate along the Northwest Coast and in the subarctic Pacific Ocean during the Last Glacial Maximum and deglaciation. The period of interest is Marine Isotope Stage 2 between ca. 29,000 calendar years ago (29 ka) and 11,700 calendar years ago (11.7 ka). The glacial history of the Northwest Coast involved multiple glacial systems responding independently to latitudinal variations in climate caused by changes in the North American ice sheets and in the tropical ocean-atmosphere system. Glaciers reached their maximum extents 1–5 kyrs later along the Northwest Coast than did large sectors of the Laurentide and Fennoscandian Ice Sheets. Local, Last Glacial Maxima were reached in a time-transgressive, north to south sequence between southwestern Alaska and Puget Sound. The history of relative sea level along the Northwest Coast during Marine Isotope Stage 2 was complex because of rapid isostatic adjustments by a thin lithosphere to these time-transgressive glacial fluctuations. Multiple lines of evidence suggest Bering Strait was first flooded by the sea after 11 ka and that it probably did not assume its present-day oceanographic functions until after 9 ka. The coldest intervals occurred during Heinrich Event 2 (ca. 26–23.5 ka), again between ca. 23 and 21.5 ka, and during Heinrich Event 1 (ca. 18–15 ka). During these times, mean annual sea surface temperatures cooled by 5o to 8o C in the Gulf of Alaska, and glacial equilibrium-line altitudes fell below present sea level in southern Alaska and along the Aleutian Island chain. Sea ice episodically expanded across the subarctic Pacific in winter. Oceanographic changes in the Gulf of Alaska tracked variations in the vigor of the Asian Summer Monsoon. The deglaciation of the Northwest Coast may have served as the trigger for global climate changes during deglaciation. Starting ca. 21 ka, marine-based glaciers there were increasingly destabilized by rising eustatic sea level and influxes of freshwater and heat associated with the rejuvenation of the Asian Summer Monsoon. Rapid retreat of marine-based glaciers began ca. 19 ka and released large numbers of ice bergs and vast amounts of freshwater into the Northeast Pacific. Resultant cooling of the North Pacific may have been teleconnected to the North Atlantic through the atmosphere, where it slowed Atlantic Meridional Overturning Circulation and initiated the global effects of Heinrich Event 1, ca. 18–15 ka. During the Younger Dryas, ca. 12.8–11.7 ka, mean annual sea surface temperatures were 4o to 6o C cooler than today in the Gulf of Alaska, and sea ice again expanded across the subarctic Pacific in winter. Conditions of extreme seasonality characterized by cold, dry winters and warm, steadily ameliorating summers caused by the southward diversion of the Aleutian Low in winter may explain the previously enigmatic records of Younger Dryas climate along the Northwest Coast. [ABSTRACT FROM AUTHOR]

The sea and lake ice concentration pan-Arctic analysis system at Environment and Climate Change Canada (ECCC) initializes both the short-range Arctic sea ice forecasting models and numerical weather prediction tools. In this study, our previously developed approach for deriving ice concentration from RADARSAT-2 was adjusted to become applicable to the RADARSAT Constellation Mission (RCM) data. This algorithm adaptation was done by incorporating RCM beam-specific wind speed retrieval models and enhancing the quality control procedure. We found an excellent agreement (correlation = 0.996) between ice concentrations derived from nearly 4000 RCM images and ice concentrations from the image analyses manually produced by the Canadian Ice Service (CIS) over a one-year period between August 1, 2020 and July 31, 2021. Then, for data assimilation experiments in the ECCC ice analysis system, we extracted ice concentrations at 1.6 km resolution from >65,000 RCM images acquired over the same test time period and over the whole Arctic. We demonstrated that assimilation of RCM-derived observations significantly improves ice analyses especially over lakes, in the vicinity to the coasts, and marginal ice zones. Accuracy of the ice analyses in the areas that are not covered by the CIS charts such as Alaska, High Arctic, and Eurasian Arctic substantially increased after the assimilation of RCM data. Visual assessment of the ice analyses against optical data showed that high-resolution details in ice concentration fields were successfully introduced by the RCM retrievals. Operational implementation of near-real-time RCM data assimilation in the ice concentration analysis system that initializes the ECCC Regional Ice-Ocean Prediction System is underway. • 65,000+ RCM images were used for assimilation. • RCM-derived ice concentrations agree very well with manually-produced ice charts. • Assimilation of RCM data improves pan-Arctic ice analyses over a 12-months period. [ABSTRACT FROM AUTHOR]

Diminishing sea ice is impacting the wave field across the Arctic region. Recent observation- and model-based studies highlight the spatiotemporal influence of sea ice on offshore wave climatologies, but effects within the nearshore region are still poorly described. This study characterizes the wave climate in the central Beaufort Sea coast from 1979 to 2019 by utilizing a wave hindcast model that uses ERA5 winds, waves, and ice concentrations as input. The spectral wave model SWAN (Simulating Waves Nearshore) is calibrated and validated based on more than 10 000 in situ time point measurements collected over a 13-year time period across the region, with friction variations and empirical coefficients for newly implemented empirical ice formulations for the open-water and shoulder seasons. Model results and trends are analyzed over the 41-year time period using the non-parametric Mann–Kendall test, including an estimate of Sen's slope. The model results show that the reduction in sea ice concentration correlates strongly with increases in average and extreme wave conditions. In particular, the open-water season extended by ∼96 d over the 41-year time period (∼2.4 d yr -1), resulting in a 5-fold increase in the yearly cumulative wave power. Moreover, the open-water season extends later into the year, resulting in relatively more open-water conditions during fall storms with high wind speeds. The later freeze-up results in an increase in the annual offshore median wave heights of 1 % yr -1 and an increase in the average number of rough wave days (defined as days when maximum wave heights exceed 2.5 m) from 1.5 in 1979 to 13.1 d in 2019. Trends in the nearshore areas deviate from the patterns offshore. Model results indicate a saturation limit for high wave heights in the shallow areas of Foggy Island Bay. Similar patterns are found for yearly cumulative wave power. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Arctic warming, manifested as thawing permafrost, loss of coastal sea ice, sea level rise, and climate-related extreme events, is particularly challenging for Indigenous people relying on wild food to sustain their livelihood and culture. The adoption of new technologies could provide specific capabilities to confront vulnerabilities associated with fishing and hunting activities, but it could also accentuate existing vulnerabilities of the communities and undermine the generic (i.e., non-specific) adaptive capacities to respond to rapid environmental and socioeconomic changes. We investigated the role of technology for building capacity to respond to challenges posed by climate change in three remote communities in northwest Arctic Alaska. We refer to technology as tools used to change how people engage or relate to landscape or society. We interviewed 35 Inuit subsistence users and used Q-sort methodologies to examine their attitudes toward technology and climate change adaptation. Communication technologies and new ways of transport have allowed harvesters to travel faster and further, and 89% of the interviewees underscored the role of technology for enhancing the specific capacity to cope with extreme weather (77%), foggy conditions (60%), and environmental changes (89%). Despite of the role technology plays in enhancing the capacity to respond to climate threats, just over half viewed technology as generally favorable for the community (54%), although most admitted there are downsides (60%), including higher financial costs (34%), increased vulnerability (23%), and time spent on maintenance (9%). Our results underscore the need to focus on generic capacity when developing climate adaptation policies for Arctic Alaska to attend to both climatic and non-climatic stressors affecting the vulnerability of Indigenous communities. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Ocean waves facilitate coastal erosion in the Arctic (and worldwide). Wave energy reaching Arctic coasts is controlled by seasonal sea ice, which includes landfast ice attached to the coastlines or sea floor, and mobile pack ice further seaward. Wave energy in the Arctic is increasing due to the loss of pack ice, and these effects are generally well‐represented in regional climate models. Landfast ice continues to form at the coast each year; when it lasts longer than pack ice, it provides protection against wave erosion. However, landfast ice is difficult to include in models which can lead them to overestimate the wave energy reaching the coasts. Using observations of waves from three coastal sites in Alaska, we demonstrate the importance of including landfast ice into regional models, and propose an effective method of combining public datasets to account for its effects on waves. These results can help the research community predict how much wave energy will be available for coastal erosion processes in the coming decades. Key Points: Year‐long observations show a seasonal cycle of wave exposure at three sites along the Arctic coast of northern AlaskaThe persistence of landfast ice in the late spring/early summer dramatically reduces the wave energy reaching the coastCoastal protection by landfast ice is not represented in global climate models, but it can be parameterized [ABSTRACT FROM AUTHOR]

There has been significant sea ice loss associated with climate change in the Pacific Arctic, with unquantified impacts to the habitat of ice-obligate marine mammals such as ringed seals (Pusa hispida). Ringed seals maintain breathing holes and excavate subnivean lairs on sea ice to provide protection from weather and predators during birthing, nursing, and resting. However, there is limited baseline information on the snow and ice habitat, distribution, density, and configuration of ringed seal structures (breathing holes, simple haul-out lairs, and pup lairs) in Alaska. Here, we describe historic field records from two regions of the eastern Chukchi Sea (Kotzebue Sound and Ledyard Bay) collected during spring 1983 and 1984 to quantify baseline ringed seal breeding habitat and map the distribution of ringed seal structures using modern geospatial tools. Of 490 structures located on pre-established study grids by trained dogs, 29% were pup lairs (25% in Kotzebue Sound and 33% in Ledyard Bay). Grids in Ledyard Bay had greater overall density of seal structures than those in Kotzebue Sound (8.6 structures/km2 and 7.1 structures/km2), but structures were larger in Kotzebue Sound. Pup lairs were located in closer proximity to other structures and characterized by deeper snow and greater ice deformation than haul-out lairs or simple breathing holes. At pup lairs, snow depths averaged 74.9 cm (range 37–132 cm), with ice relief nearby averaging 76 cm (range 31–183 cm), and ice deformation 29.9% (range 5–80%). We compare our results to similar studies conducted in other geographic regions and discuss our findings in the context of recent declines in extent and duration of seasonal cover of landfast sea ice and snow deposition on sea ice. Ultimately, additional research is needed to understand the effects of recent environmental changes on ringed seals, but our study establishes a baseline upon which future research can measure pup habitat in northwest Alaska. [ABSTRACT FROM AUTHOR]

Arctic snow and ice cover are vital indicators of climate variability and change, yet while the Arctic shows overall warming and dramatic changes in snow and ice cover, the response of these high-latitude regions to recent climatic change varies regionally. Although previous studies have examined changing snow and ice separately, examining phenology changes across multiple components of the cryosphere together is important for understanding how these components and their response to climate forcing are interconnected. In this work, we examine recent changes in sea ice, lake ice, and snow together at the pan-Arctic scale using the Interactive Multisensor Snow and Ice Mapping System 24 km product from 1997–2019, with a more detailed regional examination from 2004–2019 using the 4 km product. We show overall that for sea ice, trends toward earlier open water (-7.7 d per decade, p<0.05) and later final freeze (10.6 d per decade, p<0.05) are evident. Trends toward earlier first snow-off (-4.9 d per decade, p<0.05), combined with trends toward earlier first snow-on (-2.8 d per decade, p<0.05), lead to almost no change in the length of the snow-free season, despite shifting earlier in the year. Sea ice-off, lake ice-off, and snow-off parameters were significantly correlated, with stronger correlations during the snow-off and ice-off season compared to the snow-on and ice-on season. Regionally, the Bering and Chukchi seas show the most pronounced response to warming, with the strongest trends identified toward earlier ice-off and later ice-on. This is consistent with earlier snow-off and lake ice-off and later snow-on and lake ice-on in west and southwest Alaska. In contrast to this, significant clustering between sea ice, lake ice, and snow-on trends in the eastern portion of the North American Arctic shows an earlier return of snow and ice. The marked regional variability in snow and ice phenology across the pan-Arctic highlights the complex relationships between snow and ice, as well as their response to climatic change, and warrants detailed monitoring to understand how different regions of the Arctic are responding to ongoing changes. [ABSTRACT FROM AUTHOR]

Successful wildlife management depends upon coordination and consultation with local communities. However, much of the research used to inform management is often derived solely from data collected directly from wildlife. Indigenous people living in the Arctic have a close connection to their environment, which provides unique opportunities to observe their environment and the ecology of Arctic species. Further, most northern Arctic communities occur within the range of polar bears (nanuq, Ursus maritimus) and have experienced significant climatic changes. Here, we used semi-structured interviews from 2017 to 2019 to document Iñupiaq knowledge of polar bears observed over four decades in four Alaskan communities in the range of the Southern Beaufort Sea polar bear subpopulation: Wainwright, Utqiaġvik, Nuiqsut, and Kaktovik. All but one of 47 participants described directional and notable changes in sea ice, including earlier ice breakup, later ice return, thinner ice, and less multiyear pack ice. These changes corresponded with observations of bears spending more time on land during the late summer and early fall in recent decades--observations consistent with scientific and Indigenous knowledge studies in Alaska, Canada, and Greenland. Participants noted that polar bear and seal body condition and local abundance either varied geographically or exhibited no patterns. However, participants described a recent phenomenon of bears being exhausted and lethargic when arriving on shore in the summer and fall after extensive swims from the pack ice. Further, several participants suggested that maternal denning is occurring more often on land than sea ice. Participants indicated that village and regional governments are increasingly challenged to obtain resources needed to keep their communities safe as polar bears spend more time on land, an issue that is likely to be exacerbated both in this region and elsewhere as sea ice loss continues. [ABSTRACT FROM AUTHOR]

Recent years have seen record changes in the Arctic and circumpolar North. Rapid ice loss leading to an unprecedented lack of sea ice in Norton Sound and the greater Bering Sea for two subsequent winters caused cascading impacts on the marine ecosystem and beyond. In this article, we reflect on the underlying causes leading to the urgent situation today, and possible next steps. We argue here that methodological reform is needed to understand the full magnitude of change currently underway in this region. By broadening our evidence base for understanding the present changes, we would be better positioned to detect changes and respond with what needs to be done in the current grave circumstances. [ABSTRACT FROM AUTHOR]

The Arctic is undergoing rapid and accelerating change in response to global warming, altering biodiversity patterns, and ecosystem function across the region. For Arctic endemic species, our understanding of the consequences of such change remains limited. Spectacled eiders (Somateria fischeri), a large Arctic sea duck, use remote regions in the Bering Sea, Arctic Russia, and Alaska throughout the annual cycle making it difficult to conduct comprehensive surveys or demographic studies. Listed as Threatened under the U.S. Endangered Species Act, understanding the species response to climate change is critical for effective conservation policy and planning. Here, we developed an integrated population model to describe spectacled eider population dynamics using capture–mark–recapture, breeding population survey, nest survey, and environmental data collected between 1992 and 2014. Our intent was to estimate abundance, population growth, and demographic rates, and quantify how changes in the environment influenced population dynamics. Abundance of spectacled eiders breeding in western Alaska has increased since listing in 1993 and responded more strongly to annual variation in first‐year survival than adult survival or productivity. We found both adult survival and nest success were highest in years following intermediate sea ice conditions during the wintering period, and both demographic rates declined when sea ice conditions were above or below average. In recent years, sea ice extent has reached new record lows and has remained below average throughout the winter for multiple years in a row. Sea ice persistence is expected to further decline in the Bering Sea. Our results indicate spectacled eiders may be vulnerable to climate change and the increasingly variable sea ice conditions throughout their wintering range with potentially deleterious effects on population dynamics. Importantly, we identified that different demographic rates responded similarly to changes in sea ice conditions, emphasizing the need for integrated analyses to understand population dynamics. [ABSTRACT FROM AUTHOR]

Arctic sea ice drift motion affects the global material balance, energy exchange and climate change and seriously affects the navigational safety of ships along certain channels. Due to the Arctic's special geographical location and harsh natural conditions, observations and broad understanding of the Arctic sea ice motion are very limited. In this study, sea ice motion data released by the National Snow and Ice Data Center (NSIDC) were used to analyze the climatological, spatial and temporal characteristics of the Arctic sea ice drift from 1979 to 2018 and to understand the multiscale variation characteristics of the three major Arctic sea ice drift patterns. The empirical orthogonal function (EOF) analysis method was used to extract the three main sea ice drift patterns, which are the anticyclonic sea ice drift circulation pattern on the scale of the Arctic basin, the average sea ice transport pattern from the Arctic Ocean to the Fram Strait, and the transport pattern moving ice between the Kara Sea (KS) and the northern coast of Alaska. By using the ensemble empirical mode decomposition (EEMD) method, each temporal coefficient series extracted by the EOF method was decomposed into multiple timescale sequences. We found that the three major drift patterns have four significant interannual variation periods of approximately 1, 2, 4 and 8 years. Furthermore, the second pattern has a significant interdecadal variation characteristic with a period of approximately 19 years, while the other two patterns have no significant interdecadal variation characteristics. Combined with the atmospheric and oceanic geophysical variables, the results of the correlation analysis show that the first EOF sea ice drift pattern is mainly related to atmospheric environmental factors, the second pattern is related to the joint action of atmospheric and oceanic factors, and the third pattern is mainly related to oceanic factors. Our study suggests that the ocean environment also has a strong correlation with sea ice movement. Especially for some sea ice transport patterns, the correlation even exceeds atmospheric forcing. [ABSTRACT FROM AUTHOR]

Changing biophysical conditions due to amplified climate change in northern latitudes has significant implications for species' habitat and populations and can dramatically alter interactions between harvesters and local resources. Tribal, regional, and state governments, federal agencies, and other local planning entities have begun documenting observations of changing harvest conditions and the information necessary for communities to adapt to shifting resource availability. We identify and evaluate what stakeholders are saying about wild foods in the context of climate change information needs in Alaska through a review of published grey literature (n = 87). Documents consistently expressed that climate change was impacting habitat conditions, resource distribution, and the abundance of wild foods. They solicited more information on biophysical processes (e.g., sea ice conditions) and populationlevel responses (e.g., shift in migration patterns). They also recommended that future projects focus on information that will improve food security, travel access, and community well-being. Documents suggested that communities have successfully sustained harvest practices, but most current adaptations are localized decisions being made by harvesters to manage the risks of current climate change. Strategies include finding new areas to hunt, substituting harvest species with other wild foods, or using new modes of travel. Documents also identified several adaptation strategies that still need to be implemented, and are dependent on actions by actors at larger scales; these strategies include legal, policy, and management actions to help reduce climate change impacts to wild food harvest. This review of the grey literature complements the climate-change literature by describing information needs of Alaskan wild food harvesters as well as providing tangible suggestions about how to improve adaptation and management strategies for harvesters grappling with changing resource conditions in the Arctic. [ABSTRACT FROM AUTHOR]

We present an analysis of long‐term data collected at Utqiaġvik, Alaska, to explore the impacts of cloud processes on the probability of finding supercooled water given cloud temperature, P(L|T), in the topmost unseeded liquid‐bearing layers. P(L|T) has local minima at temperatures around −6°C and −15°C. Simulations using habit‐evolving ice microphysics models suggest that these minima are the result of efficient vapor growth by non‐isometric habits found at these temperatures. We conclude that habit‐dependent vapor growth of ice crystals modulates the macrophysical occurrence of supercooled water in polar clouds, the effect of which should be included in model parametrizations to avoid biases and/or error compensation. Our methodology is adaptable for spherical ice treatments implemented in models (example parametrizations provided), amenable for use with satellite measurements to give global impartial observational targets for model evaluations, and may allow empirical characterization of bulk responses to seeding and possibly secondary ice effects. Plain Language Summary: Clouds are responsible for the highest uncertainty in climate model predictions, partially due to deficiencies in the representation of processes controlling the temperature‐dependent cloud water phase, and hence, cloud impact on radiative transfer through the atmosphere. Here, we use long‐term measurements collected at Utqiaġvik, Alaska to examine the probability of occurrence of liquid water clouds at a range of sub‐freezing temperatures (supercooled clouds). Our methodology allows the robust characterization of occurrence of the highest supercooled cloud per measured atmospheric profile. The resultant probability enables the identification of processes affecting liquid water desiccation. An ensemble of model simulations indicates that significantly lower occurrence of supercooled clouds (by more than 20%) around certain temperatures is the result of the shape and associated rapid growth of precipitating ice crystals formed in these clouds. These fast‐growing ice crystals can dry their parent clouds' environment, occasionally resulting in cloud dissipation. We conclude that parametrization of these ice crystal growth rate effects should be included in large‐scale models to better represent polar clouds. We also suggest that our method could be easily adapted for satellite measurements to provide a valuable observational database of global supercooled cloud occurrence. Key Points: The probability of finding topmost supercooled water layers given cloud temperature, P(L|T), provides an impartial water occurrence metricP(L|T) using long‐term Arctic‐site data shows a significant (>20%) ice habit growth impact on liquid occurrence (supported by simulations)P(L|T) datasets can provide strong observational targets for models; an example parametrization for the North Slope of Alaska is provided [ABSTRACT FROM AUTHOR]

Convective storms can cause economic damage and harm to humans by producing flash floods, lightning and severe weather. While organized convection is well studied in the tropics and mid-latitudes, few studies have focused on the physics and climate change impacts of pan-Arctic convective systems. Using a convection-permitting model we showed in a predecessor study that organized convective storm frequency might triple by the end of the century in Alaska assuming a high emission scenario. The present study assesses the reasons for this rapid increase in organized convection by investigating dynamic and thermodynamic changes within future storms and their environments, in light of canonical existing theories for mid-latitude and tropical deep convection. In a future climate, more moisture originates from Arctic marine basins increasing relative humidity over Alaska due to the loss of sea ice, which is in sharp contrast to lower-latitude land regions that are expected to become drier. This increase in relative humidity favors the onset of organized convection through more unstable thermodynamic environments, increased low-level buoyancy, and weaker downdrafts. Our confidence in these results is increased by showing that these changes can be analytically derived from basic physical laws. This suggests that organized thunderstorms might become more frequent in other pan-Arctic continental regions highlighting the uniqueness and vulnerability of these regions to climate change. [ABSTRACT FROM AUTHOR]

In the Arctic, air temperatures are warming and sea ice is declining, resulting in larger waves and a longer open water season, all of which intensify the thaw and erosion of ice-rich coasts. This change in climate has been shown to increase the rate of Arctic coastal erosion, causing problems for industrial, military, and civil infrastructure as well as changes in nearshore biogeochemistry. Numerical models that reproduce historical and project future Arctic erosion rates are necessary to understand how further climate change will affect these problems, and no such model yet exists to simulate the physics of erosion on a pan-Arctic scale. We have coupled a bathystrophic storm surge model to a simplified physical erosion model of a partially frozen cliff and beach. This Arctic erosion model, called ArcticBeach v1.0, is a first step toward a parameterization of Arctic shoreline erosion for larger-scale models, which are not able to resolve the fine spatial scale (up to about 40 m) needed to capture shoreline erosion rates from years to decades. It is forced by wind speeds and directions, wave period and height, sea surface temperature, all of which are masked during times of sea ice cover near the coastline. Model tuning requires observed historical retreat rates (at least one value), as well as rough nearshore bathymetry. These parameters are already available on a pan-Arctic scale. The model is validated at two study sites at Drew Point (DP), Alaska, and Mamontovy Khayata (MK), Siberia, which are respectively located in the Beaufort and Laptev Seas, on different sides of the Arctic Ocean. Simulated cumulative retreat rates for DP and MK respectively (169 and 170 m) over the time periods studied at each site (2007 - 2016, and 1995 - 2018) are found to be within the same order of magnitude as observed cumulative retreat rates (172 and 120 m). Given the large differences in geomorphology and weather systems between the two study sites, this study provides a proof-of-concept that ArcticBeach v1.0 can be applied on very different partially frozen coastlines. ArcticBeach v1.0 provides a promising starting point to project the retreat of Arctic shorelines, or to evaluate historical retreat in places that have had few observations. Further, this model can provide estimates of the flux of sediment from land to sea for Arctic nearshore biogeochemical studies, while leaving an opportunity for further development of modelling the physics of a partially frozen shoreline. [ABSTRACT FROM AUTHOR]

Alaska's Yukon–Kuskokwim Delta (YKD) is among the Arctic's warmest, most biologically productive regions, but regional decline of the normalized difference vegetation index (NDVI) has been a striking feature of spaceborne Advanced High Resolution Radiometer (AVHRR) observations since 1982. This contrast with "greening" prevalent elsewhere in the low Arctic raises questions concerning climatic and biophysical drivers of tundra productivity along maritime–continental gradients. We compared NDVI time series from AVHRR, the Moderate Resolution Imaging Spectroradiometer (MODIS), and Landsat for 2000–19 and identified trend drivers with reference to sea ice and climate datasets, ecosystem and disturbance mapping, field measurements of vegetation, and knowledge exchange with YKD elders. All time series showed increasing maximum NDVI; however, whereas MODIS and Landsat trends were very similar, AVHRR-observed trends were weaker and had dissimilar spatial patterns. The AVHRR and MODIS records for time-integrated NDVI were dramatically different; AVHRR indicated weak declines, whereas MODIS indicated strong increases throughout the YKD. Disagreement largely arose from observations during shoulder seasons, when there is partial snow cover and very high cloud frequency. Nonetheless, both records shared strong correlations with spring sea ice extent and summer warmth. Multiple lines of evidence indicate that, despite frequent disturbances and high interannual variability in spring sea ice and summer warmth, tundra productivity is increasing on the YKD. Although climatic drivers of tundra productivity were similar to more continental parts of the Arctic, our intercomparison highlights sources of uncertainty in maritime areas like the YKD that currently, or soon will, challenge historical concepts of "what is Arctic." [ABSTRACT FROM AUTHOR]

In this study, detailed characteristics of the leading intraseasonal variability mode of boreal winter surface air temperature (SAT) over the North American (NA) sector are investigated. This intraseasonal SAT mode, characterized by two anomalous centers with an opposite sign--one over central NA and another over east Siberia (ES)/Alaska--bears a great resemblance to the ''warm Arctic-cold continent'' pattern of the interannual SAT variability over NA. This intraseasonal SAT mode and associated circulation exert a pronounced influence on regional weather extremes, including precipitation over the northwest coast of NA, sea ice concentration over the Chukchi and Bering Seas, and extreme warm and cold events over the NA continent and Arctic region. Surface warming and cooling signals of the intraseasonal SAT mode are connected to temperature anomalies in a deep-tropospheric layer up to 300 hPa with a decreasing amplitude with altitude. Particularly, a coupling between the troposphere and stratosphere is found during evolution of the intraseasonal SAT variability, although whether the stratospheric processes are essential in sustaining the leading intraseasonal SAT mode is difficult to determine based on observations alone. Two origins of wave sources are identified in contributing to vertically propagating planetary waves near Alaska: one over ES/Alaska associated with local intraseasonal variability and another from the subtropical North Pacific via Rossby wave trains induced by tropical convective activity over the western Pacific, possibly associated with the Madden-Julian oscillation. [ABSTRACT FROM AUTHOR]

In the Arctic, during polar night and early spring, ice clouds are separated into two leading types of ice clouds (TICs): (1) TIC1 clouds characterized by a large concentration of very small crystals and TIC2 clouds characterized by a low concentration of large ice crystals. Using a suitable parameterization of heterogeneous ice nucleation is essential for properly representing ice clouds in meteorological and climate models and subsequently understanding their interactions with aerosols and radiation. Here, we describe a new parameterization for ice crystal formation by heterogeneous nucleation in water-subsaturated conditions coupled to aerosol chemistry in the Weather Research and Forecasting model coupled with chemistry (WRF-Chem). The parameterization is implemented in the two-moment cloud microphysics scheme, and we assess how the WRF-Chem model responds to the run-time interaction between chemistry and the new parameterization. Well-documented reference cases provided us with in situ data from the spring 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) over Alaska. Our analysis reveals that the new parameterization clearly improves the representation of the ice water content (IWC) in polluted or unpolluted air masses and shows the poor performance of the reference parameterization in representing ice clouds with low IWC. The new parameterization is able to represent TIC1 and TIC2 microphysical characteristics at the top of the clouds, where heterogenous ice nucleation is most likely occurring, even with the known bias of simulated aerosols by WRF-Chem over the Arctic. [ABSTRACT FROM AUTHOR]