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The paper assesses the chemical transformation of surface waters in the southeastern part of the Khibiny Mountainous Massif after launching the Oleniy Ruchey apatite–nepheline ore deposit in 2012. The influence of the Oleniy Ruchey Mine was reflected in an increase in water mineralization (by an order of magnitude) and in a change in the basic ion ratios in water objects receiving runoff from mines, rock, and tailing dumps compared to the watercourses unaffected by the mining enterprise's activities. Natural hydrocarbonate–sodium water with a mineralization of 10 mg/L was transformed into the nitrate–sodium or sulfate–calcium water. The content of nitrogen group compounds in the Lake Komarinoe water, which receives wastewater from the tailing dumps over the ten-year history of the mining and processing plant, has increased by two orders of magnitude, and the nitrate became basic ion. The concentrations of other basic ions and mineralization in this lake increased by an order of magnitude, as the content of trace elements (Sr, F, Mo), which belong to the main rock-forming minerals of apatite–nepheline deposits. Compared to the background water bodies, the mine wastewaters have the elevated mineralization (up to 260 mg/L), pH value (up to 10), and a modified chemical composition. They are characterized by a hydrocarbonate–sodium composition with a large proportion of nitrates and sulfates. Mine wastewaters have elevated contents of nutrient compounds, organic matter, and some trace elements (Al, Fe, Sr, Cu, Mn, Zn, and Cr). It has been established that the geochemical modifications in the quality of surface water are locally developed, being typical of water bodies receiving wastewater from a mining enterprise, in contrast to metallurgical plants, the atmospheric emissions of which caused pollution over tens and hundreds km. [ABSTRACT FROM AUTHOR]

Palynomorphs are one of the few groups of fossils that provide biostratigraphic control in marine to nonmarine rocks and can be applied as proxies for paleoenvironmental and paleoclimatic interpretations. Their utility is enhanced by their microscopic size, which is usually less than 200 micrometres; they are thus easily recovered from small rock samples. They occur throughout the Phanerozoic and are therefore invaluable in refining biostratigraphic control of Arctic successions in Alaska, Arctic Canada, Greenland, northern Europe, and northern Russia. The objective of the Circum-Arctic Palynological Event (CAPE) Stratigraphy series of papers is to integrate data published on Arctic palynomorphs to delineate palynological events (palynoevents) across the Arctic for the Silurian to Cenozoic. Once the series of papers is complete, the data will also be used to compile a TimeScale Creator datapack that can be updated and calibrated on an ongoing basis. Palynoevents include taxon originations (first occurrences or FOs) and extinctions (last occurrences, or LOs) and some abundance events. The palynoevents are correlated with established chronostratigraphic horizons such as bases of ammonoid zones or stages, and hence their chronostratigraphy is independent of the absolute time scale in millions of years. In addition to the palynostratigraphic papers, the series includes a paper detailing the paleogeography of the circum-Arctic regions, including informative maps, as well as a paper providing a palynological perspective of the Cenozoic shift from greenhouse to icehouse conditions. [ABSTRACT FROM AUTHOR]

Climate change represents one of the most pressing societal and scientific challenges of our time. While much of the current research on climate change focuses on future prediction, some of the strongest signals of warming can already be seen in Arctic and alpine areas, where temperatures are rising faster than the global average, and in the oceans, where the combination of rising temperatures and acidification due to increased CO 2 concentrations has had catastrophic consequences for sensitive marine organisms inhabiting coral reefs. The scientific papers highlighted as part of this anniversary issue represent some of the most impactful advances in our understanding of the consequences of anthropogenic climate change. Here, we reflect on the legacy of these papers from the biotic perspective.

Recently, the developments of ethics and politics in the Arctic region have again become an issue for international discussion. One main issue is the problem of climate change and sustainability of the Arctic region. This problem is linked to the issue of exploitation of natural resources in the Arctic region, not at least in Greenland. Indeed, the general issue is how we should define ethics of the environment and sustainability as a general principle for the Arctic region. It is important to discuss what is at stake and how we define the problem in relation to the different participating stakeholders. This paper deals with these problems as a case for global ethics and it proposes a vision of ethical and political responsibility for sustainable development in order to deal with such problems. [ABSTRACT FROM AUTHOR]

In order to describe the Arctic system I propose using a concept functionally equivalent to territoriality, namely aquatoriality. Whether communicating about territoriality or aquatoriality, concepts and delimitations are both contingent to forms of communication systems. I will distinguish between six communications systems that differentiated from each other could become involved in the new deals emerging around the Arctic. Apart of an economic communication code about the Arctic, a legal code, ecological communication codes, and tourist communication codes, I will cope with the military coding of the Arctic. These codes could then appear structurally coupled to a political system that in an organizational way appears in the Arctic Council. [ABSTRACT FROM AUTHOR]

In the context of climate change, research on frozen soils has attracted much attention in recent years, and numerous research papers have been published on these topics in the last decade. However, the present status and developmental trends in frozen soils research have not been reported systematically. Herein, a bibliometric analysis was conducted using 7,108 research papers on frozen soils published between 2010 and 2019. The results indicate that: (a) although the number of articles published increased from 432 in 2010 to 1,066 in 2019, the average number of citations per paper reached a maximum of 5.40 in 2014, and subsequently decreased to 2.99 in 2019; (b) China, the USA, and Canada ranked first to third in terms of total papers; (c) the most popular author keywords were boreal, tundra, Landsat, lakes, decomposition, dissolved organic carbon, permafrost thaw, and carbon cycle; and (d) the five most popular research topics in 2010–2019 were the characteristics and factors influencing frozen soils, the Arctic carbon cycle under the background of its complex environment, permafrost changes on the Qinghai–Tibet Plateau in the context of climate change, ancient frozen soils in various historical periods, and frozen soils in the Arctic. [ABSTRACT FROM AUTHOR]

The 'smart city' has received growing attention as a concept that could play an essential role in the sustainability of the Arctic. Today, the idea is associated with information and communication technology (ICT) when used in urban areas to improve quality of life, offer more efficient and effective use of cities' infrastructures, foster social inclusion, and mitigate environmental harm. However, the relationship between smart cities and Arctic sustainability remains ambiguous, especially from perspectives beyond those of techno-optimism. Our aim in this paper is to critically discuss the value of smart city concept for Arctic cities, from an urban dynamic perspective. To this end, this paper reflects on how the sustainability of Arctic cities can be challenged by urban dynamics in metrics for (1) smart city development, (2) politics and bureaucratization, and (3) the role of citizens. The paper has several implications for academia, practitioners, and policymakers: for the former, it advances an alternative debate to explore the complex relations between smart city development and Arctic sustainability; for practitioners and policymakers, it indicates the problematic but often hidden side of smart city development, stressing the need to carefully translate the concept and its promises to fit the unique Arctic context. [ABSTRACT FROM AUTHOR]

Land use conflicts are intensifying in Northern Sweden due to the increasing global demand for resources coupled with the green transition. In line with this, a thorough understanding of land use conflicts in the area is becoming necessary as economic activities expand and newer ones are developed. Hence, this paper aims to provide a systematic literature review of research on land use conflicts specific to Northern Sweden, focusing on various economic activities such as forestry, mining, tourism, energy sector and reindeer husbandry. Additionally, we aim to determine lessons learned and suggested ways forward based on a systematic review. We used Scopus and Web of Science on June 2023 and through descriptive statistical analysis of 33 articles, we summarized research trends and gaps. We found three main typologies of conflicts and five main themes of suggested ways forward. Recommendations agree that there should be a broader understanding of the underlying interests of the stakeholders; and there should be an inclusive, more participatory approach to discussing potential solutions, not to create an agreement but to come to an understanding. Beyond academic insights, the findings hold practical relevance for shaping effective land use policies. This paper offers valuable lessons that extend beyond the local context, informing broader discussions and policy considerations for sustainable land management in the larger Arctic setting, where similar challenges and resource demands are unfolding. [ABSTRACT FROM AUTHOR]

Ships' logbooks are now an accepted part of the repertoire of data sources in climate change studies. This article examines some of the particular issues surrounding logbooks from the Arctic region in the so-called pre-instrumental period. Attention is given to the means by which narrative descriptions of wind, weather and sea ice cover can be reliably expressed in index form. Consideration is also given to the various means by which these data can be most effectively managed for scientific analysis as in most cases they were not recorded for such purposes. Many such logbooks remain yet to be digitized and the methods described here can be applied with equal confidence in future through such undertakings using English language documents. [ABSTRACT FROM AUTHOR]

This paper takes up the call for political geographers to engage more directly with Wittgenstein's later philosophy of language, namely his emphasis on language as activity and practice. In particular, it considers his approach to linguistic demonstration over representation, whereby the reader is not 'told' but 'shown.' This arguably instructive conceptualisation of the functioning of language is here applied to a space of geopolitics, focusing on the political potentialities of articulating an Arctic otherwise through selective bilingualism and language‐use. More specifically, the paper centres on the particular use of North Sámi language in a conference space otherwise dominated by English and Norwegian. The act of 'articulating otherwise' is not here an act of defiance but rather an invitation for re‐conceptualisation. In making Indigenous voices heard on their own terms, it is not only the words but even more so the act of their utterance that carries political power. The paper therefore argues that political geographers ought to (re)direct attention to language‐use and the socio‐political practices of linguistic world‐making. By drawing on Wittgenstein's approach to language‐use, what here becomes clear is that geopolitical questions too are negotiated not through given answers but rather through the interactive process of reaching these together – insights that in turn allow us to consider how agency and change may play out through language‐use, potentially articulating geopolitics otherwise. This paper takes up the call for political geographers to engage more directly with Wittgenstein's later philosophy of language, namely his emphasis on language as activity and practice. The paper focuses on the potentialities of articulating an Arctic otherwise through selective bilingualism and Sámi language‐use in a conference space. It argues that political geographers ought to (re)direct attention to language‐use and the socio‐political practices of linguistic world‐making. [ABSTRACT FROM AUTHOR]

This paper introduces the Special Issue of The Journal of the Acoustical Society of America on Ocean Acoustics in the Changing Arctic. The special issue includes papers on ocean (and in one case atmospheric) acoustics. Changes in both the ice cover and ocean stratification have significant implications for acoustic propagation and ambient sound. The Arctic is not done changing, and papers in this special issue, therefore, represent a snapshot of current acoustic conditions in the Arctic. [ABSTRACT FROM AUTHOR]

Global warming is causing unprecedented changes to permafrost regions with amplified effects in the Arctic through a phenomenon known as Arctic amplification. This intensified climate warming thaws both the discontinuous and continuous permafrost resulting in changes in the mechanical properties of the soils found in these regions. Since permafrost regions constitute nearly 24% of the Northern Hemisphere, understanding the strength of soils in thawed conditions is essential to analyze the stability of existing structures, and to design safer and more economical infrastructure in these regions. Specifically, thawing of the permafrost is causing considerable reductions in its strength of soils, which may lead to massive landslides, foundation failures, and so forth. Since frozen soil is a multiphase structure that consists of soil particles, unfrozen water, ice, and air, each constituent will influence the mechanical properties. This paper reviews the current state of knowledge of the impact of temperature, volumetric ice content, unfrozen water content, and frozen density on the compressive strength, peak shear strength, residual shear strength, undrained shear strength, and tensile strength of soils. The undrained shear strength of soil is said to have a linear correlation with temperature. In addition, the undrained cohesion of soil was found to depend on the temperature, whereas the undrained friction angle of soil was significantly influenced by volumetric ice content. An increase in the volumetric ice content up to 80% to 90% will cause a reduction in the peak and residual deviatoric stresses. In addition, an increase in volumetric ice content resulted in an increase in the compressive strength of the soil. The tensile and compressive strengths were found to be functions of the unfrozen water content. Global warming is causing the temperature of the permafrost, which is permanently frozen ground, to rise. This paper provides valuable insights into the impact of the changes in this ambient temperature on the strength of frozen soils in permafrost regions for a wide range of applications. Such insights are crucial for the design of resilient and stable infrastructure, such as foundations, embankments, and retaining walls, in which consideration of the reduced strength of thawed soils due to climate change will be necessary. In addition, the knowledge will allow for better management of vulnerable areas prone to landslides and erosion caused by the weakened soil strength permitting the implementation of mitigation measures before lives are lost and costly economic damages are incurred. Finally, this information will aid in early warning systems, emergency planning, and decision making to minimize the impact of hazards on human settlements and infrastructure. In this paper, a review of the current state of knowledge regarding the strength of frozen soils and the associated fluctuations in these strengths because of a rise in temperature are presented. Guidelines on the best practices for sample preparation and testing along with correlations to estimate various strength parameters are also provided. [ABSTRACT FROM AUTHOR]

By exhaustively reviewing the literature related to marine geohazards, this paper reports on their uncertainties. Examples of marine geohazards include submarine landslides, fluid flows in the underground, scour events, and seabed gouging by ice. Key uncertain variables of interest to marine geohazard assessments are identified and structured by relating a framework defining the main generic components of any risk description to the task of describing risk in the marine geohazards field. Furthermore, issues related to the sources of uncertainty are scrutinised and some recommendations on how to address the identified large uncertainties in geohazard risk assessments are made. Specific considerations are proposed for analysing geohazards in the Arctic, where exploration and development activities are currently regaining momentum. Ultimately, based on the large uncertainties identified, we also strive to identify knowledge gaps to orientate scientific research efforts in the field of marine geohazards. [ABSTRACT FROM AUTHOR]

The new sea ice configuration GSI6.0, used in the Met Office global coupled configuration GC2.0, is described and the sea ice extent, thickness and volume are compared with the previous configuration and with observationally-based datasets. In the Arctic, the sea ice is thicker in all seasons than in the previous configuration, and there is now better agreement of the modelled concentration and extent with the HadISST dataset. In the Antarctic, a warm bias in the ocean model has been exacerbated at the higher resolution of GC2.0, leading to a large reduction in ice extent and volume; further work is required to rectify this in future configurations. [ABSTRACT FROM AUTHOR]

This Special Issue aims to highlight research articles focusing on the geographical scale of glacier and lake ice variations, as well as the engineering scale of ice properties and their practical applications via laboratory tests and numerical modeling. Additionally, it includes research on ecosystems under lake ice. The main goal is successfully achieved through the joint efforts of authors, anonymous reviewers, and editorial managers. In total, 1 review article and 15 research articles are included in this Special Issue. These articles cover a wide range of topics, including water resources from Chinese mountain glacier variation; lake ice phenology at different latitudes and altitudes around the world; ice properties from laboratory experiments and numerical modeling; ice engineering with different purposes in China and the Arctic; and ecosystem under lake ice at different temporal and spatial scales. This Special Issue received contributions from researchers from different parts of China and from Chinese international cooperation partners because of its focus on "higher temperature ice" under global warming. All papers presented are innovative and of high quality. This Special Issue can promote research on ice properties and their applications in practices ranging from mountains to sea, especially in popular water ecosystem environments under ice during seasonal ice period. [ABSTRACT FROM AUTHOR]

Model simulations of the fate of numerous hypothetical substances in the global environment can provide considerable insight into how an organic chemical's degradability and partitioning properties influence its absolute and relative Arctic enrichment behavior, as quantified by the Arctic Contamination Potential. For substances that degrade faster in water than in soil, but are quite persistent in the atmosphere, highest Arctic contamination is expected to occur if the substances have intermediate volatility and high hydrophobicity. Organic substances that are degradable in the atmosphere can still accumulate in the Arctic if they are soluble and highly persistent in water. These latter substances, which reach the Arctic in the ocean, also show the highest potential for relative enrichment in the Arctic, i.e., high amounts in northern high latitudes relative to the amounts in the total global environment. Beyond a threshold persistence in surface media of the order of several months to a year, chemical degradability leads to further relative enrichment. This is because only chemicals that are sufficiently long-lived get transferred to polar regions and once there can persist longer than at lower latitudes. The model simulations can inform the search for new potential Arctic contaminants, and can highlight combinations of properties which should be avoided in high production volume chemicals with the potential for environmental release. Three categories of organic substances are singled out for troublesome combinations of persistence, distribution, and potential bioaccumulation characteristics, only one of which contains "classical" Arctic POPs. Examples of potential Arctic contaminants within each of these categories are named. [ABSTRACT FROM AUTHOR]

The present paper seeks to lay bare how the grim realities of settler colonialism and petro-capitalism have a tolling effect on the indigenous ways of life. The present era, termed the 'Anthropocene' or 'Capitalocene,' as it is the capitalist concern of some of the privileged anthropos that inflict socio-economic and ecological injustices on earth, heralds the birth of cautionary literature that deconstructs anthropocentric fixation to purge the earth off the catastrophic impacts of rapacious human activities. In order to examine how capitalism and its resultant climate emergency have spurred environmental activists and authors to reflect upon this theme, the paper undertakes a close textual analysis of The Breathing Hole (2020) by Colleen Murphy (b. 1954), a contemporary Quebecois playwright. By employing indigenous ecocriticism and non-human turn in literary studies, the study examines how the playwright jettisons the standardised category of the Anthropos by prioritising the non-human character, Angu'ruaq, an anthropomorphised polar bear. Attempts have been made to highlight how the capitalist motive of the neo-colonial agents leaves a breach in the fabric of the succouring connection between the indigenous Inuit existence and the non-human beings in the Nunavut territory of the Canadian Arctic. The findings of the paper demonstrate how the playwright approaches contemporary eco-crisis using indigenous ecodrama. [ABSTRACT FROM AUTHOR]

This paper presents the first results of sea ice detection using the data of Ka- and Ku-band radars at low incidence angles. A classification method based on an unsupervised K-means approach is applied to the arrays of the data for the Arctic and Antarctic regions. Comparison with Advanced Microwave Scanning Radiometer 2 (AMSR-2) data was performed, and the dependence of classification performance was evaluated for incidence angles from 0° to 18.15°. This paper evaluates the classification accuracy of sea ice detection based on Ku-band, Ka-band, and their combination. Preliminary results indicate that the classification based solely on Ku-band data achieves the best performance. [ABSTRACT FROM AUTHOR]

The atmospheric ozone plays an important role in understanding of the processes occurring in the atmosphere and changes in the climate. Total ozone observations in Siberia were performed by Brewer MKIV No. 049 spectrophotometer in Tomsk, Western Siberia and SAOZ UV-Vis spectrometers deployed along the Arctic Circle in Salekhard aerological station since 1998 and Zhigansk aerological station in Eastern Siberia since 1991. We also use 2Z-ECC ozonesondes for ozone profile observations in winter-spring period at the Salekhard aerological station at the in Western Siberia and ECC-6A sondes at the drifting North Pole station NP-38 in the Central Arctic area. During the winter-spring season in 2011, Arctic ozone in the 19-21 km altitude region was observed to be more than 70% less that typical values. In the winter-spring of 2012, on the other hand, Arctic conditions were overall much warmer than in 2011, and no evidence of significant ozone loss was seen above the Asiatic regions of Russian Federation. The aim of the paper is to describe which and where these measurements were carried out and illustrate their performances by some examples of ozone data measured in Western and Eastern Siberia, Russia such as that which occurred in the winter-spring season of 2011. [ABSTRACT FROM AUTHOR]

Soil carbon stored in high-latitude permafrost landscapes is threatened by warming, and could contribute significant amounts of carbon to the atmosphere and hydrosphere as permafrost thaws. Permafrost disturbances, especially active layer detachments and retrogressive thaw slumps, have increased in frequency and magnitude across the Fosheim Peninsula, Ellesmere Island, Canada. To determine the effects of retrogressive thaw slumps on net ecosystem exchange (NEE) of CO2 in high Arctic tundra, we used two eddy covariance (EC) tower systems to simultaneously and continuously measure CO2 fluxes from a disturbed site and the surrounding undisturbed tundra. During the 32-day measurement period in the 2014 growing season the undisturbed tundra was a small net sink (NEE = −0.12 g C m-2 d-1); however, the disturbed terrain of the retrogressive thaw slump was a net source (NEE = +0.39 g C m-2 d-1). Over the measurement period, the undisturbed tundra sequestered 3.84 g C m-2, while the disturbed tundra released 12.48 g C m-2. Before full leaf out in early July, the undisturbed tundra was a small source of CO2, but shifted to a sink for the remainder of the sampling season (July), whereas the disturbed tundra remained a source of CO2 throughout the season. A static chamber system was also used to measure fluxes in the footprints of the two towers, in both disturbed and undisturbed tundra, and fluxes were partitioned into ecosystem respiration (Re) and gross primary production (GPP). Average GPP and Re found in disturbed tundra were smaller (+0.41 μmol m-2 s-1 and +0.50 μmol m-2 s-1, respectively) than those found in undisturbed tundra (+1.21 μmol m-2 s-1 and +1.00 μmol m-2 s-1, respectively). Our measurements indicated clearly that the permafrost disturbance changed the high Arctic tundra system from a sink to a source for CO2 during the growing season. [ABSTRACT FROM AUTHOR]

The article presents a study of the assimilation of observed ice concentration and freeboard information into a global coupled ocean-sea-ice model using an Ensemble Kalman Filter system. It evaluates the efficiency and impact of the data assimilation on ice concentration. Results demonstrate that the simulated Antarctic and Arctic sea-ice are improved using the assimilation of synthetic ice concentration data.

The ice surface temperature (IST) is an important boundary condition for both atmospheric and ocean and sea ice models and for coupled systems. An operational ice surface temperature product using satellite Metop AVHRR infra-red data was developed for MyOcean. The IST can be mapped in clear sky regions using a split window algorithm specially tuned for sea ice. Clear sky conditions are prevailing during spring in the Arctic while persistent cloud cover limits data coverage during summer. The cloud covered regions are detected using the EUMETSAT cloud mask. The Metop IST compares to 2m temperature at the Greenland ice cap Summit within STD error of 3.14 °C and to Arctic drifting buoy temperature data within STD error of 3.69 °C. A case study reveal that the in situ radiometer data versus satellite IST STD error can be much lower (0.73 °C) and that the different in situ measures complicates the validation. Differences and variability between Metop IST and in situ data are analysed and discussed. An inter-comparison of Metop IST, numerical weather prediction temperatures and in situ observation indicates large biases between the different quantities. Because of the scarcity of conventional surface temperature or surface air temperature data in the Arctic the satellite IST data with its relatively good coverage can potentially add valuable information to model analysis for the Arctic atmosphere. [ABSTRACT FROM AUTHOR]

Throughout history, small village communities in the Arctic have developed several strategies to ensure their survival. Along the Torne River, some fishing communities have produced specific architectures, landscapes, and social strategies to support their communities and survive for centuries. However, depopulation, aging, climate change, and the expansion of the extraction industry are threatening these villages. The hypothesis is that traditional fishing villages situated alongside rivers possess architectural, urban, and social attributes that can enhance outdoor activities linked to water and green spaces and enable the long-term social sustainability of Arctic villages. The innovative approach of the paper involves combining a mapping methodology of green and blue infrastructure with the architectural, urban, social and historical values of a place to identify design strategies for improving attractiveness demonstrating its efficacy, particularly in small, local-scale villages. The paper investigates the villages of Kukkola and Korpikylä taken as emblematic examples and explores the architectural and landscape value in relation to the green–blue infrastructure. [ABSTRACT FROM AUTHOR]

In recent decades, the atmospheric moisture capacity has increased globally in concert with global warming, with a particularly notable warming trend in Arctic regions. However, due to limited observational data, the variation and causes of polar precipitation, especially large-scale precipitation events associated with Arctic cyclones, remain unclear. In this paper, GPM satellite data are compared with ERA5 reanalysis data to explore the characteristics of summer precipitation at the northern margin of the Eurasian region (NMER) and the influence of cyclone activity on precipitation. It is revealed that high precipitation values in the Arctic region, as indicated by the GPM and ERA5 data, are mainly concentrated at the NMER. However, the GPM data show an overall larger precipitation amount, while the station observations more closely agree with the ERA5 precipitation changes at the NMER. The cyclone identification results indicate that summer cyclones at the NMER are mainly distributed in the Barents, Kara and Laptev Seas, and the precipitation contribution rate of ERA5-derived cyclones is 37.35%, which is significantly higher than that of GPM-derived cyclones (29.47%). Furthermore, high cyclone activity results in more intense precipitation, with the top 5% of the strongest cyclones contributing 60% (GPM) and 40% (ERA5) to the total cyclonic precipitation. [ABSTRACT FROM AUTHOR]

The Ku band microwave scatterometer (SCA) and scanning microwave radiometer (SMR) onboard HaiYang-2B (HY-2B) can simultaneously supply active and passive microwave observations over the polar region. In this paper, a polar ice water discrimination model and Arctic sea-ice-type classification model based on the support vector machine (SVM) method were established and used to produce a daily sea ice extent dataset from 2019 to 2021 with data from SCA and SMR. First, suitable scattering and radiation parameters are chosen as input data for the discriminant model. Then, the sea ice extent was obtained based on the monthly ice water discrimination model, and finally, the ice over the Arctic was classified into multiyear ice (MYI) and first-year ice (FYI). The 3-year ice extent and MYI extent products were consistent with the similar results of the National Snow and Ice Data Center (NSIDC) and Ocean and Sea Ice Satellite Application Facility (OSISAF). Using the OSISAF similar product as validation data, the overall accuracies (OAs) of ice/water discrimination and FYI/MYI discrimination are 99% and 97%, respectively. Compared with the high spatial resolution classification results of the Moderate Resolution Imaging Spectroradiometer (MODIS) and SAR, the OAs of ice/water discrimination and FYI/MYI discrimination are 96% and 86%, respectively. In conclusion, the SAC and SMR of HY-2B have been verified for monitoring polar sea ice, and the sea ice extent and sea-ice-type products are promising for integration into long-term sea ice records. [ABSTRACT FROM AUTHOR]

This paper introduces the special collection in Geophysical Research Letters and Journal of Geophysical Research: Atmospheres on the exceptional stratospheric polar vortex in 2019/2020. Papers in this collection show that the 2019/2020 stratospheric polar vortex was the strongest, most persistent, and coldest on record in the Arctic. The unprecedented Arctic chemical processing and ozone loss in spring 2020 have been studied using numerous satellite and ground‐based data sets and chemistry‐transport models. Quantitative estimates of chemical loss are broadly consistent among the studies and show profile loss of about the same magnitude as in the Arctic in 2011, but with most loss at lower altitudes; column loss was comparable to or larger than that in 2011. Several papers show evidence of dynamical coupling from the mesosphere down to the surface. Studies of tropospheric influence and impacts link the exceptionally strong vortex to reflection of upward propagating waves and show coupling to tropospheric anomalies, including extreme heat, precipitation, windstorms, and marine cold air outbreaks. Predictability of the exceptional stratospheric polar vortex in 2019/2020 and related predictability of surface conditions are explored. The exceptionally strong stratospheric polar vortex in 2019/2020 highlights the extreme interannual variability in the Arctic winter/spring stratosphere and the far‐reaching consequences of such extremes. Plain Language Summary: The Arctic stratospheric polar vortex—a band of strong winds roughly encircling the pole at about 65°N latitude from about 15 to 50 km above the Earth's surface that forms every winter—was exceptionally strong during the 2019/2020 winter. The strong vortex in the stratosphere was linked to unusual conditions at both higher and lower altitudes. This collection of papers explores the far‐reaching consequences of the exceptionally strong stratospheric polar vortex in 2019/2020, including impacts on Arctic chemical ozone loss and on surface weather conditions. Chemical ozone loss in spring 2020 matched or exceeded the most previously on record (for 2011) and showed some features similar to the larger loss that occurs over the Antarctic every spring. The exceptionally strong stratospheric polar vortex was linked to weather extremes, including record heat, unusual patterns of precipitation, marine cold air outbreaks, and windstorms. Key Points: The stratospheric polar vortex in 2019/2020 was the strongest and longest‐lasting on record as described in this special collectionThis exceptionally strong and cold polar vortex led to unprecedented Arctic ozone loss, approaching that in some Antarctic wintersCirculation anomalies linked to the vortex spanned the mesosphere to the surface with implications for extreme weather and predictability [ABSTRACT FROM AUTHOR]

Permafrost is degrading across regions of the Arctic, which can lead to increases in nutrient concentrations in surface freshwaters. The oligotrophic state of many arctic lakes suggests that enhanced nutrient inputs may have important effects on these systems, but little is known about microbial nutrient limitation patterns in these lakes. We investigated microbial extracellular enzyme activities (EEAs) to infer seasonal nutrient dynamics and limitation across 24 lakes in southwest Greenland during summer (June and July). From early to late summer, enzyme activities that indicate microbial carbon (C), nitrogen (N), and phosphorus (P) demand increased in both the epilimnia and hypolimnia by 74% on average. Microbial investment in P acquisition was generally higher than that for N. Interactions among EEAs indicated that bacteria were primarily P limited. Dissolved organic matter (DOM, measured as dissolved organic carbon) was strongly and positively correlated with microbial P demand (R2 = 0.84 in July), while there were no relationships between DOM and microbial N demand. Microbial P limitation in June epilimnia (R² = 0.67) and July hypolimnia (R2 = 0.57) increased with DOM concentration. The consistency of microbial P limitation from June to July was related to the amount of DOM present, with some low DOM lakes becoming N-limited in July. Our results suggest that future changes in P or DOM inputs to these lakes are likely to alter microbial nutrient limitation patterns. [ABSTRACT FROM AUTHOR]

Low-centre polygonal terrain developing within gentle sloping surfaces and lowlands in the high Arctic have a potential to retain snowmelt water in their bowl-shaped centre and as such are considered high latitude wetlands. Such wetlands in the continuous permafrost regions have an important ecological role in an otherwise generally arid region. In the valley of the glacier C-79 on Bylot Island (Nunavut, Canada), thermal erosion gullies are rapidly eroding the permafrost along ice wedges affecting the integrity of the polygons by breaching and collapsing the surrounding rims. While intact polygons were characterized by a relative homogeneity (topography, snow cover, maximum active layer thaw depth, ground moisture content, vegetation cover), eroded polygons had a non-linear response for the same elements following their perturbation. The heterogeneous nature of disturbed terrains impacts active layer thickness, ground ice aggradation in the upper portion of permafrost, soil moisture and vegetation dynamics, carbon storage and terrestrial green-house gas emissions. [ABSTRACT FROM AUTHOR]

Ponds and lakes are widespread across the rapidly changing permafrost environments. Aquatic systems play an important role in global biogeochemical cycles, especially in greenhouse gas (GHG) exchanges between terrestrial systems and the atmosphere. The source, speciation and emission of carbon released from permafrost landscapes are strongly influenced by local specific conditions rather than general environmental setting. This study reports on GHG ages and emission rates from aquatic systems on Bylot Island in the eastern Canadian Arctic. Dissolved and ebullition gas samples were collected during the summer season from different types of water bodies located in a highly dynamic periglacial valley: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes overlying unfrozen soils (talik). The results showed strikingly different ages and fluxes depending on aquatic system types. Polygonal ponds were net sinks of dissolved CO2, but variable sources of dissolved CH4. They presented the highest ebullition fluxes, one or two orders of magnitude higher than from other ponds and lakes. Trough ponds appeared as substantial GHG sources, especially when their edges were actively eroding. Both types of ponds produced modern to hundreds of years old (< 550 yr BP) GHG, even if trough ponds could contain much older carbon (> 2000 yr BP) derived from freshly eroded peat. Lakes had small dissolved and ebullition fluxes, however they released much older GHG, including millennium-old CH4 (up to 3500 yr BP) sampled from lake central areas. Acetoclastic methanogenesis dominated at all study sites and there was minimal, if any, methane oxidation in gas emitted through ebullition. These findings provide new insights on the variable role of permafrost aquatic systems as a positive feedback mechanism on climate. [ABSTRACT FROM AUTHOR]

The article focuses on a study on the remote sensing of thin clouds in the Arctic Region. It describes the methodology of the study in which interferometer measurements were used to analyze the datasets of single-layer clouds derived from the DOE Atmospheric Radiation Measurement Program (ARM) North Slope of Alaska. It concludes the advantages of remote sensing in to characterize thin clouds.

We assessed the relationship between zooplankton metabolism (respiration and inorganic N and P excretion) and "in situ" temperature through a grid of stations representing a range of natural temperature variation during the ATOS-Arctic cruise (July 2007). The objective was to explore not only the direct effects of temperature on O2 consumption and NH4-N and PO4-P excretion, but also to investigate the possible relationships between temperature and the stoichiometry of the metabolic products. Zooplankton metabolic rates increased according to the rising temperature conditions, following the Arrhenius equation. However, the activation energy differed for the various metabolic processes considered. Respiration was the metabolic activity less affected by temperature, followed by NH4-N and PO4-P excretion, and as a consequence the values of the C: N, C: P and N: P quotients of the metabolic products were inversely related to temperature. The effects of temperature on the stoichiometry of the excretion products would contribute to modify the nutrient pool available for phytoplankton and induce qualitative and quantitative shifts in the characteristics of primary producers that could possibly translate into the whole Arctic marine food web. [ABSTRACT FROM AUTHOR]

We present a detailed description of TOPAZ4, the latest version of TOPAZ - a coupled ocean-sea ice data assimilation system for the North Atlantic Ocean and Arctic. It is the only operational, large-scale ocean data assimilation system that uses the ensem- ble Kalman filter. This means that TOPAZ features a time-evolving, state-dependent estimate of the state error covariance. Based on results from the pilot MyOcean reanalysis for 2003-2008, we demonstrate that TOPAZ4 produces a realistic estimate of the ocean circulation and the sea ice. We find that the ensemble spread for temperature and sea-level remains fairly constant throughout the reanalysis demonstrating that the data assimilation system is robust to ensemble collapse. Moreover, the ensemble spread for ice concentration is well correlated with the actual errors. This indicates that the ensemble statistics provide reliable state-dependent error estimates - a feature that is unique to ensemble-based data assimilation systems. We demonstrate that the quality of the reanalysis changes when different sea surface temperature products are assimilated, or when in situ profiles below the ice in the Arctic Ocean are assimilated. We find that data assimilation improves the match to independent observations compared to a free model. Improvements are particularly noticeable for ice thickness, salinity in the Arctic, and temperature in the Fram Strait, but not for transport estimates or underwater temperature. At the same time, the pilot reanalysis has revealed sev20 eral flaws in the system that have degraded its performance. Finally, we show that a simple bias estimation scheme can effectively detect the seasonal or constant bias in temperature and sea-level. [ABSTRACT FROM AUTHOR]

As the Arctic and its rivers continue to warm, a better understanding of the possible future impacts on people would benefit from close partnership with Indigenous communities and scientists from diverse fields of study. We present efforts by the Arctic Rivers Project to conduct community‐engaged research to increase collective understanding of the historical and potential future impacts of climate change on rivers, fish, and Indigenous communities. Working in central to northern Alaska and the Yukon Territory in Canada, the project seeks to engage with Indigenous communities in ethical and equitable ways to produces science that is useful, useable, and used that may serve as an example for future research efforts. Toward this goal, we formed an Indigenous Advisory Council and together developed project‐specific knowledge co‐production protocols. This paper provides a novel model of design and implementation to co‐produce knowledge with communities across a large study domain. Plain Language Summary: The Arctic and rivers located in the Arctic and subarctic are warming due to climate change. To understand the impacts this warming will have on people, partnering with impacted Indigenous communities in the region is important. It is also important that these partnerships are ethical and equitable and produce science that is actionable. This paper discusses efforts undertaken by a specific project, the Arctic Rivers Project, to conduct ethical and equitable research with Indigenous communities and generate science that is useful to those communities. Through this research our goal is to better understand potential future impacts of climate change on rivers, fish, and Indigenous communities in central northern Alaska and the Yukon Territory in Canada. To achieve this goal, the project formed an Indigenous Advisory Council (IAC) and together developed guidelines for how we can work collaboratively with Indigenous communities. Our specific process of forming an IAC and guidelines is, to our knowledge, a new way to approach collaborative research when working across a large geographic area. We present our process here so that it may provide an example for other research efforts. Key Points: Arctic climate information can be made useful, useable, and used by equitably accounting for diverse community adaptation needs through knowledge co‐productionInstitutional and community capacity, including means and ability, is necessary for equitable knowledge co‐production to occurWe present an approach for co‐producing knowledge with Indigenous communities that can serve as an example for other scientific efforts [ABSTRACT FROM AUTHOR]

The Arctic is undergoing rapid changes due to global warming, including the expansion of the marginal ice zone (MIZ), a zone of mixed ice and open water surfaces. To predict the atmospheric interaction with these surfaces, a critical process in climate models, this paper examines a simplified theoretical framework to non-dimensionalize the dynamics of the atmospheric boundary layer (ABL) over a mixed ice-water surface (MIZ–ABL). A heterogeneity Richardson number, Ri h , is proposed to account for the difference in temperature between the ice and water surface in relation to the synoptic pressure gradient forcing. With the wind angle relative to the ice-water interface, α , this framework hypothesizes that these two dimensionless numbers, regardless of individual dimensional variables (surface temperature and geostrophic wind speed) are sufficient to predict the MIZ–ABL dynamics. To test this framework, large-eddy simulations were employed over half-ice and half-water surfaces, with varying surface temperatures and geostrophic wind velocities. While the surface heat fluxes over ice, water, and the aggregate surface seem to be captured reasonably well by α and Ri h , the mean wind and turbulent kinetic energy (TKE) profiles were not, suggesting that not only the difference in stability between the two surface, but also the individual stabilities over each surface influence the dynamics. The wind angle had a significant impact on the results, both in terms of heat fluxes at the surface, turbulent and dispersive fluxes in the MIZ–ABL, and the structure of the secondary circulations. When wind blows perpendicular to the water-ice interface, internal boundary layers are favoured except at the highest Ri h simulated. For cases with wind parallel to the interface, large rolls parallel to the shore emerge. The paper raises at least as many questions as it answers, highlighting the need for further studies of the MIZ–ABL. [ABSTRACT FROM AUTHOR]

In early studies, northern vegetation response to global warming recognised both increases in biomass/cover and shrinking of species' distributional ranges. Subsequent field measurements focussed on vegetation cover and biomass increases ("greening"), and more recently decreases ("browning"). However, satellite observations show that more than 50% of arctic vegetation has not changed significantly despite rapid warming. While absence of change in remote sensing data does not necessarily mean no ecological change on the ground, the significant proportion of the Arctic that appears to be stable in the face of considerable climate change points to a greater need to understand Arctic ecosystem stability. In this paper, we performed an extensive review of the available literature to seek balances or imbalances between research focussing on "greening", "browning" and "stability/no change". We find that greening studies dominate the literature though two relatively small areas of the Arctic are disproportionately represented for this main change process. Critically, there are too few studies anywhere investigating stability. We highlight the need to understand the mechanisms driving Arctic ecosystem stability, and the potential longer-term consequences of remaining stable in a rapidly changing climate. [ABSTRACT FROM AUTHOR]

The hydrographic properties of the Kongsfjorden -- Krossfjorden system (79° N, Spitsbergen) are affected by Atlantic water incursions as well as glacier meltwater runoff. This results in strong physical gradients (temperature, salinity and irradiance) within the fjords. Here, we tested the hypothesis that glaciers affect phytoplankton dynamics as early as the productive spring bloom period. During two campaigns in 2007 (late spring) and 2008 (early spring) we studied hydrographic characteristics and phytoplankton variability along 2 transects in both fjords, using HPLC-CHEMTAX pigment fingerprinting, molecular fingerprinting (DGGE) and sequencing of 18S rRNA genes. The sheltered inner fjord locations remained colder during spring as opposed to the outer locations. Vertical light attenuation coefficients increased from early spring onwards, at all locations, but in particular at the inner locations. During the end of spring, meltwater input had stratified surface waters throughout the fjords. The inner fjord locations were characterized by overall lower phytoplankton biomass. Furthermore HPLC-CHEMTAX data revealed that diatoms and Phaeocystis sp. were replaced by small nano- and picophytoplankton during late spring, coinciding with low nutrient availability. The innermost stations showed higher relative abundances of nano- and picophytoplankton throughout, notably of cyanophytes and cryptophytes. Molecular fingerprinting revealed a high similarity between inner fjord samples from early spring and late spring samples from all locations, while outer samples from early spring clustered separately. We conclude that glacier influence, mediated by early meltwater input, modifies phytoplankton biomass and composition already during the spring bloom period, in favor of low biomass and small cell size communities. This may affect higher trophic levels especially when regional warming further increases the period and volume of meltwater. [ABSTRACT FROM AUTHOR]

Global warming has accelerated the formation of permafrost thaw ponds in several subarctic and arctic regions. These ponds are net heterotrophic as evidenced by their greenhouse gas (GHG) supersaturation levels (CO2 and CH4), and generally receive large terrestrial carbon inputs from the thawing and eroding permafrost. We measured seasonal and vertical variations in the concentration and type of dissolved organic matter (DOM) in five subarctic thaw (thermokarst) ponds in northern Quebec, and explored how environmental gradients influenced heterotrophic and phototrophic biomass and productivity. Late winter DOM had low aromaticity indicating reduced inputs of terres trial carbon, while the high concentration of dissolved organic carbon (DOC) suggests that some production of non-chromophoric dissolved compounds by the microbial food web took place under the ice cover. Summer DOM had a strong terrestrial signature, but was also characterized with significant inputs of algal-derived carbon, especially at the pond surface. During late winter, bacterial production was low (maximum of 0.8mgCm-3 d-1) and was largely based on free-living bacterioplankton (58%). Bacterial production in summer was high (up to 58mgCm3 d1), dominated by particleattached bacteria (67%), and strongly correlated to the amount of terrestrial carbon. Primary production was restricted to summer surface waters due to strong light limitation deeper in the water column or in winter. The phototrophic biomass was equal to the heterotrophic biomass, but as the algae were mostly composed of mixotrophic species, most probably they used bacteria rather than solar energy in such shaded ponds. According to the δ13C analyses, non-algal carbon supported 51% of winter and 37% of summer biomass of the phantom midge larvae, Chaoborus sp., that are at the top of the trophic chain. Our results point to a strong heterotrophic energy pathway 25 in these thaw pond ecosystems, where bacterioplankton dominates the production of new carbon in both summer and winter. [ABSTRACT FROM AUTHOR]

The HYCOM-NORWECOM modeling system is used both for basic research and as a part of the forecasting system for the Arctic Marine Forecasting Centre through the MyOcean project. Here we present a revised version of this model. The present model, as well as the sensitivity simulations leading up to this version, has been compared to a dataset of in-situ measurements of nutrient and chlorophyll from the Norwegian Sea and the Atlantic sector of the Arctic Ocean. The revisions having most impact included adding diatoms to the diet of micro-zooplankton, increasing micro-zooplankton grazing rate and decreased silicate-to-nitrate ratio in diatoms. Model runs are performed both with a coarse- (~ 50km) and higher-resolution (~ 15 km) model configuration, both covering the North Atlantic and Arctic Ocean. While the new model formulation improves the results in both the coarse- and high-resolution model, the nutrient bias is smaller in the high-resolution model, probably as a result of the better resolution of the main processes and with that improved circulation. The final revised version delivers satisfactory results for all three nutrients as well as improved result for chlorophyll in terms of the annual cycle amplitude. However, for chlorophyll the correlation with in-situ data remains relatively low. Besides the large uncertainties associated with observational data this is possibly caused by the fact that constant C/N and Chl/N ratios are implemented in the model. [ABSTRACT FROM AUTHOR]

Over the last four decades, organic-walled dinoflagellate cysts have shown high potential as tracers of past sea-surface conditions during the Quaternary. These microfossils relate to the pelagic productivity of both phototrophic and heterotrophic protist organisms and are recovered in high numbers in almost all marine environment settings from the nearshore and estuarine systems to the distal continental margin. In polar environments, where other conventional proxies are rare or absent, dinoflagellate cysts showed a relatively high diversity of species and a close relationship with sea-ice cover duration, winter and summer temperature, and salinity, enabling quantitative reconstructions of several oceanic variables over time. From the temperate to the tropical latitudes of the Atlantic Ocean, their modern distribution highlights a response to primary productivity and seasonal contrasts in surface temperature. They also have proven that they could be used as tracers of eutrophication in stratified systems and can also highlight human impact on their distribution. In this paper, we present an overview of dinoflagellate cysts as ecological tracers in recent and past sediments of the Atlantic Ocean, from the Arctic to the Antarctic. We provide examples of their use as proxies in paleoclimatic-palaeoceanographic studies at glacial to interglacial time scales, with emphasis on the last ice age to recent (last 25 kyr), the northern North Atlantic and western-eastern tropic North Atlantic. We also discuss their potential as tracers of anthropogenic stress in coastal environments. [ABSTRACT FROM AUTHOR]

Increased warming in the Arctic is of great concern. This is particularly due to permafrost degradation, which is expected to accelerate microbial breakdown of soil organic carbon, with its further release into the atmosphere as carbon dioxide (CO2). The fine-scale variability of CO2 fluxes across highly mosaic Arctic tundra landscapes can provide us with insights into the diverse responses of individual plant communities to environmental change. In the paper, we contribute to filling existing gaps by investigating the variability of CO2 flux rates within different landscape units for dominant vegetation communities and plant species across typical tundra of the southern part of the Taimyr Peninsula, Siberia. In general, the variability of soil CO2 flux illustrates a four-fold increase from non-vascular vegetation, mainly lichens and mosses (1.05 ± 0.36 µmol m−2 s−1), towards vascular plants (3.59 ± 0.51 µmol m−2 s−1). Barren ground ("frost boils") shows the lowest value of 0.79 ± 0.21 µmol m−2 s−1, while considering the Arctic "browning" phenomenon, a further substantial increase of CO2 flux can be expected with shrub expansion. Given the high correlation with top soil temperature, well-drained and relatively dry habitats such as barren ground and non-vascular vegetation are expected to be the most sensitive to the observed and projected temperature growth in the Arctic. For mixed vegetation and vascular species that favor wetter conditions, soil moisture appears to play a greater role. Based on the modeled seasonal pattern of soil CO2 flux and precipitation records, and applying the rainfall simulations in situ we outlined the role of precipitation across enhanced CO2 emissions (i.e., the "Birch" effect). We found that a pulse-like growth of soil CO2 fluxes, observed within the first few minutes after rainfall on vegetated plots, reaches 0.99 ± 0.48 µmol m−2 s−1 per each 1 mm of precipitation, while barren ground shows 55–70% inhibition of CO2 emission during the first several hours. An average additive effect of precipitation on soil CO2 flux may achieve 7–12% over the entire growing season, while the projected increased precipitation regime in the Arctic may strengthen the total CO2 release from the soil surface to the atmosphere during the growing season. [ABSTRACT FROM AUTHOR]

The cloud feedback may result in amplification or damping of Arctic warming. Two common techniques used to diagnose the top‐of‐the‐atmosphere cloud feedback are the Adjusted Cloud Radiative Effect (AdjCRE) method and the Cloud Radiative Kernel (CRK) method. We apply both to CMIP5 and CMIP6 model data, finding that the AdjCRE calculated Arctic shortwave cloud feedback is twice as correlated with sea ice loss in CMIP5, and four times in CMIP6, as the CRK method. We find that the CRK method produces Arctic all‐sky residual percentages exceeding 20% in 15 of 18 models. We use the CRK method to decompose the feedback in CMIP5 and CMIP6 finding that its median value changed from negative to positive driven by a less‐negative cloud optical depth feedback. Despite its lack of closure, we conclude that the CRK method is better suited for Arctic SW feedbacks as it is less impacted by surface albedo changes. Plain Language Summary: The cloud feedback is the process by which cloud property changes in a warming climate can either further enhance warming or damp it. The Arctic is warming faster than the rest of the globe, and one of the largest sources of uncertainty in its climate projections is the cloud feedback. There are two popular methods to calculate the cloud feedback: the Adjusted Cloud Radiative Effect technique, and the Cloud Radiative Kernel technique. In this paper we compare the two methods in a suite of climate models by considering the extent to which changes in Arctic sea ice impact the cloud feedbacks. From this analysis we conclude that the Cloud Radiative Kernel method is less affected by sea ice loss. We then apply the Cloud Radiative Kernel technique to data from the two most recent generations of global climate models to investigate how polar day Arctic cloud feedbacks have changed between these generations. We find that the median value of these Arctic feedbacks is slightly positive in the newest generation of models, a change from slightly negative in the previous generation that is largely fueled by a weakening of the feedback associated with changes in cloud optical depth. Key Points: The Cloud Radiative Kernel method is less sensitive to surface albedo changes than the Adjusted Cloud Radiative Effect techniqueThe Cloud Radiative Kernel method provides poor radiative closure in a suite of global climate modelsThe median shortwave Arctic cloud feedback in recent climate models is slightly positive due to a weakened cloud optical depth feedback [ABSTRACT FROM AUTHOR]

The sea ice albedo can amplify global climate change and affect the surface energy in the Arctic. In this paper, the data from Visible and Infra-Red Radiometer (VIRR) onboard Fengyun-3C satellite are applied to derive the Arctic sea ice albedo. Two radiative transfer models, namely, 6S and FluxNet, are used to simulate the reflectance and albedo in the shortwave band. Clear sky sea ice albedo in the Arctic region (60°~90°N) from 2016 to 2019 is derived through the physical process, including data preprocessing, narrowband to broadband conversion, anisotropy correction, and atmospheric correction. The results are compared with aircraft measurements and AVHRR Polar Pathfinder-Extended (APP-x) albedo product and OLCI MPF product. The bias and standard deviation of the difference between VIRR albedo and aircraft measurements are −0.040 and 0.071, respectively. Compared with APP-x product and OLCI MPF product, a good consistency of albedo is shown. And analyzed together with melt pond fraction, an obvious negative relationship can be seen. After processing the 4-year data, an obvious annual trend can be observed. Due to the influence of snow on the ice surface, the average surface albedo of the Arctic in March and April can reach more than 0.8. Starting in May, with the ice and snow melting and melt ponds forming, the albedo drops rapidly to 0.5–0.6. Into August, the melt ponds begin to freeze and the surface albedo increases. [ABSTRACT FROM AUTHOR]

This paper presents a methodological tool for dynamic reconstruction of the state of the ocean, based, as an example, on observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) experiment. The data used in this study were collected in the Amundsen Basin between October 2019 and January 2020. Analysing observational data to assess tracer field and upper-ocean dynamics is highly challenging when measurement platforms drift with the ice pack due to continuous drift speed and direction changes. We have equipped the new version of the coastal branch of the global Finite-volumE sea ice–Ocean Model (FESOM-C) with a nudging method. Model nudging was carried out assuming a quasi-steady state. Overall, the model can reproduce the lateral and vertical structure of the temperature, salinity, and density fields, which allows for projecting dynamically consistent features of these fields onto a regular grid. We identify two separate depth ranges of enhanced eddy kinetic energy located around two maxima in buoyancy frequency: the depth of the upper halocline and the depth of the warm (modified) Atlantic Water. Simulations reveal a notable decrease in surface layer salinity and density in the Amundsen Basin towards the north but no significant gradient from east to west. However, we find a mixed-layer deepening from east to west, with a 0.084 m km -1 gradient at 0.6 m km -1 standard deviation, compared to a weak deepening from south to north. The model resolves several stationary eddies in the warm Atlantic Water and provides insights into the associated dynamics. The model output can be used to further analyse the thermohaline structure and related dynamics associated with mesoscale and submesoscale processes in the central Arctic, such as estimates of heat fluxes or mass transport. The developed nudging method can be utilized to incorporate observational data from a diverse set of instruments and for further analysis of data from the MOSAiC expedition. [ABSTRACT FROM AUTHOR]

The paper reports the first results of an experiment in northern Finland during winter 2022–2023 that aimed at studying seismic events caused by seasonal freezing in the so-called critical zone (CZ) of the Earth. These events have attracted public attention recently, as multiple reports about them from local inhabitants in Arctic and sub-Arctic areas appeared on social networks. To make an instrumental study of such events, to reveal the relationship between their occurrence and winter weather conditions, and to evaluate the possible hazard, we installed two high-resolution seismic arrays with co-located soil temperature stations at two sites in Finland, one of them being in the city of Oulu in the sub-Arctic area (65.04° N, 25.61° E) and the other one above the polar circle in the municipality of Sodankylä (67.36° N, 26.63° E). The equipment recorded continuous seismic and soil temperature data during November 2022–April 2023. Based on reports from the inhabitants of Talvikangas (Oulu) about the ground shaking and unusual noises on 6 January 2023 and their observations of new fractures on the roads there, we selected the time interval for the identification of frost quakes that originated during that day from continuous seismic records in Talvikangas and in Sodankylä. During the selected time interval, the extremely rapid air temperature drops of about -1.4 °C h -1 in Talvikangas and -0.88 °C h -1 in Sodankylä were observed. We identified and located two types of seismic events – namely, frost quakes with frequencies of about 10–20 Hz, with waveforms like those of tectonic events, and irregularly shaped frost tremors with frequencies of about 120–180 Hz. The sources of frost quakes in Talvikangas are mainly located on irrigated wetland, while in Sodankylä, about 50 % of registered frost quakes were caused by ice fracturing on the Kitinen River. However, several relatively strong events, with their origin in the wetlands, were also recorded. A significant number of sources of frost tremors are confined to wetland areas cut by irrigation channels and to roads cleaned from snow during winter both in Talvikangas and in Sodankylä. We calculated ground accelerations and ground velocities for the strongest events from both groups and compared them to equivalent properties of other seismic signals, like distant local earthquakes in the area, mining production blasts, and cargo train vibration. Our study shows that high-frequency frost tremors corresponding to surface fracture opening in the uppermost frozen surface layer of a thickness of up to 5 cm can directly damage infrastructure objects like roads and basements of buildings. Surface waves, produced by frost quakes and propagating inside the shallow soil layer, have large enough ground accelerations at epicentral distances of hundreds of metres. Therefore, frost quakes should be considered a phenomenon that can potentially damage infrastructures, and they have to be taken into account in seismic hazard assessments. Our research is the first instrumental study of seismic events originating from wetland areas. These events occur as a result of the interaction between the uppermost layer of the solid Earth's CZ and atmosphere processes that deserves further study. [ABSTRACT FROM AUTHOR]

Science, engineering, and society increasingly require integrative thinking about emerging problems in complex systems, a notion referred to as convergence science. Due to the concurrent pressures of two main stressors—rapid climate change and industrialization, Arctic research demands such a paradigm of scientific inquiry. This perspective represents a synthesis of a vision for its application in Arctic system studies, developed by a group of disciplinary experts consisting of social and earth system scientists, ecologists, and engineers. Our objective is to demonstrate how convergence research questions can be developed via a holistic view of system interactions that are then parsed into material links and concrete inquiries of disciplinary and interdisciplinary nature. We illustrate the application of the convergence science paradigm to several forms of Arctic stressors using the Yamal Peninsula of the Russian Arctic as a representative natural laboratory with a biogeographic gradient from the forest‐tundra ecotone to the high Arctic. Plain Language Summary: This paper represents a synthesis of conceptual analyses, case study analyses, and practical thoughts on the application of convergence science in Arctic change studies. During a virtual workshop in 2020, a diverse, multi‐national team of authors consisting of social scientists, engineers, earth system scientists, and ecologists came together to formulate broad, scientifically, and societally important questions on how the Arctic system in the Yamal Peninsula of Western Siberia responds to pressures of rapidly changing climate and increasing industrialization. The team "engineered" a novel approach for expert (representing a disciplinary domain) and non‐expert (representatives of other disciplines) communication and at the workshop conclusion developed several convergence science questions of high appeal. Three of such questions are presented in this manuscript to illustrate how the search and identification of appropriate mechanistic linkages are critical to the development of system‐level understanding of stressor impact propagation. The need to understand underlying disciplinary and cross‐disciplinary mechanisms connecting Arctic system elements is viewed to be an inherent part of the convergence science approach. Through pursuit of such understanding, the approach naturally leads to other novel emerging questions, thereby stimulating further application of the process of integrative thinking. Key Points: Arctic research demands convergence science as essential method to understand impacts from novel stressorsAn integrative approach is developed by a diverse team to formulate questions that cannot be fully addressed within disciplinary studiesA convergence science analysis is illustrated for three questions applicable to Yamal, Russian Arctic, a microcosm of the changing Arctic [ABSTRACT FROM AUTHOR]

This paper presents the results of a multidisciplinary study with the aim of assessing the potential combined risk from consuming locally harvested food products in the Euro-Arctic region of Norway, Finland, and Russia. The three important contaminant groups—radioactive substances, heavy metals, and persistent organic pollutants (POPs)—were measured in food samples such as berries, mushrooms, fish, birds, reindeer, and moose; they were sampled in 2013–2015. To assess the combined pollution levels and investigate the trends, similarities, and variations between different contaminant groups, subsequent multivariate statistical analysis was performed. The results showed that, in general, the levels of radioactive substances, toxic elements, and POPs were below the permitted EU maximum content in food products. However, statistical analysis revealed some correlations, similarities, and peculiarities between the accumulation of different contaminants in various species, which allowed for a better understanding of the mechanisms of accumulation and interaction between different contaminant groups. It also gave a better insight into the possible added risks and helped pinpoint species that could serve as reference markers for the accumulation of different contaminants in food. Mushrooms, fish, and reindeer were found to be important markers in the combined risk assessments for the contents of metals and radioactive substances. Further research, as well as the development of methodologies for combined assessments, are recommended. [ABSTRACT FROM AUTHOR]

The bacterially mediated aerobic methane oxidation (MOx) is a key mechanism in controlling methane (CH4) emissions from the world's oceans to the atmosphere. In this study, we investigated MOx in the Arctic fjord Storfjorden (Spitsbergen) by applying a combination of radio-tracer based incubation assays (³H-CH4 and 14C-CH4), stable C-CH4 isotope measurements, and molecular tools (16S rRNA DGGE-fingerprinting, pmoA- and mxaF gene analyses). Strofjorden is stratified in the summertime with melt water (MW) in the upper 60m of the water column, Arctic water (ArW) between 60-100m and brine-enriched shelf water (BSW) down to 140 m. CH4 concentrations were supersaturated with respect to the atmospheric equilibrium (~3 nM) throughout the water column, increasing from ~20nM at the surface to a maximum of 72nM at 60m and decreasing below. MOx rate measurements at near in situ CH4 concentrations (here measured with ³H-CH4 raising the ambient CH4 pool by < 2 nM) showed a similar trend: low rates at the sea surface increasing to a maximum of ~2.3nMd-1 at 60m followed by a decrease in the deeper ArW/BSW. In contrast, rate measurements with 14C-CH4 at elevated CH4 concentrations (incubations were spiked with ~450nM of 14C-CH4, providing an estimate of the CH4 oxidation potential) showed comparably low turnover rates (< 1 nMd-1) at 60 m, but peaked in ArW/BSW at ~100m water depth, concomitant with increasing 14C-values in the residual CH4 pool. Our results indicate that the MOx community in the surface MW is adapted to relatively low CH4 concentrations. In contrast, the activity of the deep water MOx community is relatively low at the ambient, summertime CH4 concentrations but has the potential to increase rapidly in response to CH4 availability. A similar distinction between surface and deep water MOx is also suggested by our molecular analyses. Although, we found pmoA and maxF gene sequences throughout the water column attesting the ubiquitous presence of MOx communities in Storfjorden, deep water amplicons of pmoA and maxF were unusually long. Also a DGGE band related to the known Type I MOx Mehtylosphera was observed in deep BWS, but absent in surface MW. Apparently, different MOx communities have developed in the stratified water masses in Storfjorden, which is possibly related to the spatiotemporal variability in CH4 supply to the distinct water masses. [ABSTRACT FROM AUTHOR]

Spectrally resolved efficiency (i.e. apparent quantum yield, AQY) of carbon monoxide (CO) photoproduction is a useful indicator of substrate photoreactivity and a crucial parameter for modeling CO photoproduction rates in the water column. Recent evidence has suggested that CO photoproduction from particles in marine waters is significant compared to the well-known CO production from chromophoric dissolved organic matter (CDOM) photodegradation. Although CDOM-based CO AQY spectra have been extensively determined, little is known of this information on the particulate phase. Using water samples collected from the Mackenzie estuary, shelf, and Canada Basin in the Southeastern Beaufort Sea, the present study for the first time quantified the AQY spectra of particle-based CO photoproduction and compared them with the concomitantly determined CDOM-based CO AQY spectra. CO AQYs of both particles and CDOM decreased with wavelength but the spectral shape of the particulate AQY was flatter in the visible regime. This feature resulted in a disproportionally higher visible light-driven CO production by particles, thereby increasing the ratio of particle- to CDOM-based CO photoproduction with depth in the euphotic zone. In terms of depth-integrated production in the euphotic zone, CO formation from CDOM was dominated by the ultraviolet (UV, 290-400 nm) radiation whereas UV and visible light played roughly equal roles in CO production from particles. Spatially, CO AQY of bulk particulate matter (i.e. the sum of organics and inorganics) augmented from the estuary to shelf to basin while CO AQY of CDOM trended inversely. Water from the deep chlorophyll maximum layer revealed higher CO AQYs than did surface water for both particles and CDOM. CO AQY of bulk particulate matter exceeded that of CDOM on the shelf and in the basin but the sequence reversed in the estuary. Mineral absorption-corrected CO AQY of particulate organic matter (POM) was, however, greater than its CDOM counterpart in all three sub-regions and displayed magnitudes in the estuary that were no inferior to those in shelf and offshore waters. In terms of CO photoproduction, POM was thus more photoreactive than CDOM, irrespective of the organic matter's origins (i.e. terrigenous or marine). Riverine CDOM exhibited higher photoreactivity than marine CDOM and land-derived POM appeared similarly or more photoreactive than marine POM. AQY-based modeling indicates that CO photoproduction in the study area is underestimated by 13-48% if the particulate term is ignored. [ABSTRACT FROM AUTHOR]