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Between 2012 and 2018 we mapped near‐peak seasonal snow depths across two swaths covering 126 km2 in Northern Alaska using aerial structure‐from‐motion photogrammetry and lidar surveys. The surveys were validated by over a hundred thousand ground‐based depth measurements. Using a quantitative method for identifying drift areas, we conducted a snowdrift census that showed on average 18% of the study area is covered by snowdrifts each winter, with 40% of the snow‐water‐equivalent contained in the drifts. Within the census we identified six types of drifts, some of which fill each winter, others which do not. The seasonal drift evolution was distinctly different in the two swaths, a result largely explained by topographic differences. Using four metrics from the field of image quality analysis, we tested the year‐to‐year fidelity of these drift patterns, finding overall high year‐to‐year similarity, but with higher similarity values for filling drifts, and higher similarity values in one swath versus the other, again a function of the topography. These high drift fidelity values are best explained by climatically convergent winter‐cumulative windblown snow fluxes interacting with drift traps to produce the same drifts year after year. However, due to the existence of filling versus nonfilling drifts, and a predicted increasing frequency of rain‐on‐snow events in the Arctic, future snowdrift patterns and drift evolution pathways in the Arctic could diverge from those of today, with direct hydrologic impacts. Key Points: Arctic snowdrifts are landscape features important for hydrology (comprising 18% of the area but 40% of the snow‐water‐equivalent)Novel methods for snowdrift identification (quantitative) and classification (quanitative) are introduced to produce drift censusesArctic snowdrift and scour patterns repeat with exceptional fidelity each winter—but could be disrupted by a changing climate [ABSTRACT FROM AUTHOR]

Although three‐dimensional (3D) seismic surveys have improved the success rate of exploratory drilling for oil and gas, the impacts have received little scientific scrutiny, despite affecting more area than any other oil and gas activity. To aid policy‐makers and scientists, we reviewed studies of the landscape impacts of 3D‐seismic surveys in the Arctic. We analyzed a proposed 3D‐seismic program in northeast Alaska, in the northern Arctic National Wildlife Refuge, which includes a grid 63,000 km of seismic trails and additional camp‐move trails. Current regulations are not adequate to eliminate impacts from these activities. We address issues related to the high‐density of 3D trails compared to 2D methods, with larger crews, more camps, and more vehicles. We focus on consequences to the hilly landscapes, including microtopography, snow, vegetation, hydrology, active layers, and permafrost. Based on studies of 2D‐seismic trails created in 1984–1985 in the same area by similar types of vehicles, under similar regulations, approximately 122 km2 would likely sustain direct medium‐ to high‐level disturbance from the proposed exploration, with possibly expanded impacts through permafrost degradation and hydrological connectivity. Strong winds are common, and snow cover necessary to minimize impacts from vehicles is windblown and inadequate to protect much of the area. Studies of 2D‐seismic impacts have shown that moist vegetation types, which dominate the area, sustain longer‐lasting damage than wet or dry types, and that the heavy vehicles used for mobile camps caused the most damage. The permafrost is ice rich, which combined with the hilly topography, makes it especially susceptible to thermokarst and erosion triggered by winter vehicle traffic. The effects of climate warming will exacerbate the impacts of winter travel due to warmer permafrost and a shift of precipitation from snow to rain. The cumulative impacts of 3D‐seismic traffic in tundra areas need to be better assessed, together with the effects of climate change and the industrial development that would likely follow. Current data needs include studies of the impacts of 3D‐seismic exploration, better climate records for the Arctic National Wildlife Refuge, especially for wind and snow; and high‐resolution maps of topography, ground ice, hydrology, and vegetation. [ABSTRACT FROM AUTHOR]

Mercury is deposited to the Polar Regions during springtime atmospheric mercury depletion events (AMDEs) but the relationship between snow and ice crystal formation and mercury deposition is not well understood. The objective of this investigation was to determine if mercury concentrations were related to the type and formation of snow and ice crystals. On the basis of almost three hundred analyses of samples collected in the Alaskan Arctic, we suggest that kinetic crystals growing from the vapor phase, including surface hoar, frost flowers, and diamond dust, yield mercury concentrations that are typically 2-10 times higher than that reported for snow deposited during AMDEs (∼80 ng/L). Our results show that the crystal type and formation affect the mercury concentration in any given snow sample far more than the AMDE activity prior to snow collection. We present a conceptual model of how snow grain processes including deposition, condensation, reemission, sublimation, and turbulent diffusive uptake influence mercury concentrations in snow and ice. These processes are time dependent and operate collectively to affect the retention and fate of mercury in the cryosphere. The model highlights the importance of the formation and postdeposition crystallographic history of snow or ice crystals in determining the fate and concentration of mercury in the cryosphere. [ABSTRACT FROM AUTHOR]

One expected response to climate warming in the Arctic is an increase in the abundance and extent of shrubs in tundra areas. Repeat photography shows that there has been an increase in shrub cover over the past 50 years in northern Alaska. Using 202 pairs of old and new oblique aerial photographs, we have found that across this region spanning 620 km east to west and 350 km north to south, alder, willow, and dwarf birch have been increasing, with the change most easily detected on hill slopes and valley bottoms. Plot and remote sensing studies from the same region using the normalized difference vegetation index are consistent with the photographic results and indicate that the smaller shrubs between valleys are also increasing. In Canada, Scandinavia, and parts of Russia, there is both plot and remote sensing evidence for shrub expansion. Combined with the Alaskan results, the evidence suggests that a pan-Arctic vegetation transition is underway. If continued, this transition will alter the fundamental architecture and function of this ecosystem with important ramifications for the climate, the biota, and humans. [ABSTRACT FROM AUTHOR]

We divide the Alaskan Arctic cold season into five stages based on transitions in climatological and thermophysical conditions in the atmosphere, snowpack, and soil active layer. Each of these stages has distinct characteristics which drive ecosystem processes. During the two autumnal stages (Early Snow and Early Cold) soils remain warm, unfrozen water is present, and the highest rates of cold-season soil respiration occur. The next two stages (Deep Cold and Late Cold) are characterized by a frozen active layer with decreasing temperature. Thaw is critical in determining the length of the growing season and the resumption of biological processes. Deep Cold and Late Cold result from a radiation deficit, show little interannual variation, and will be resistant to change under almost any reasonable climate change scenario. These are also the stages with the least amount of biological activity and have the least impact on the ecosystem. However, Early Snow, Early Cold and Thaw stages vary significantly from year to year, have more ecosystem implications, and are also the most likely to undergo significant change in timing and character as the arctic climate changes. This 5-fold subdivision is useful for framing discussions of biophysical interactions during the arctic winter and for focusing attention on critical cold-season periods. [ABSTRACT FROM AUTHOR]

ABSTRACT In the Arctic, where wind transport of snow is common, the depth and insulative properties of the snow cover can be determined as much by the wind as by spatial variations in precipitation. Where shrubs are more abundant and larger, greater amounts of drifting snow are trapped and suffer less loss due to sublimation. The snow in shrub patches is both thicker and a better thermal insulator per unit thickness than the snow outside of shrub patches. As a consequence, winter soil surface temperatures are substantially higher, a condition that can promote greater winter decomposition and nutrient release, thereby providing a positive feedback that could enhance shrub growth. If the abundance, size, and coverage of arctic shrubs increases in response to climate warming, as is expected, snow-shrub interactions could cause a widespread increase (estimated 10%-25%) in the winter snow depth. This would increase spring runoff, winter soil temperatures, and probably winter CO: emissions. The balance between these winter effects and changes in the summer energy balance associated with the increase in shrubs probably... [ABSTRACT FROM AUTHOR]

Presents a study which showed evidence for a widespread increase in shrub abundance in Arctic landscape over a period of 50 years based on a comparison of historic and modern aerial photographs. Analysis of the photographs taken; Description of the study area; Findings.

Abstract: We collected surface snow samples during three years (2004, 2005, and 2007) in Arctic Alaska and from the adjoining frozen Arctic Ocean during springtime in environments that span most Arctic terrains including land, thin and thick first-year sea ice, and multi-year sea ice. The snow was analyzed for Br−, Cl−, SO4 2−, NO3 −, NH4 +, Na+, K+, Mg2+ and Ca2+. Source fractionation processes and atmospheric influences are important modification mechanisms that influence the ions. We find that Cl−, K+ and Mg2+ are primarily sourced by unfractionated sea salt and only show deviations from sea salt composition at low Na+ concentrations. Bromide and Ca2+ are highly influenced by atmospheric processes that are evident at low sea salt tracer concentrations. Calcium enrichments are due to the addition of non-sea salt (nss) Ca2+ from dust and possibly other sources. Bromide enrichments are due to the addition of nss-Br− and bromide depletions are due to bromine activation to the gas phase. Sulfate is affected by source fractionation at high Na+ concentrations and by atmospheric addition at low Na+ concentrations. Nitrate and NH4 + are not correlated with sea salt and show less concentration variability than sea salt ions. Modifications are related to time-integrated air–snow exchange fluxes for Br−, SO4 2− and Ca2+ and are in good agreement with observations of related gas-phase and aerosol species. This work reinforces our understanding of air–snow exchanges and their importance for atmospheric chemistry in the Arctic. [Copyright &y& Elsevier]