Arctic freshwater biodiversity is rapidly changing due to climate warming, resource extraction, infrastructure development, and landscape transformation. To improve understanding, predict future responses, and inform policy formulation, research needs must be clearly identified. Using a horizon scan survey, Arctic freshwater experts from government, international agencies, and Indigenous Peoples identified 77 biodiversity research questions with 17 highlighted as most important for near term assessment. These questions span nine thematic categories: biodiversity and taxonomic challenges, hydrological change, productivity and food webs, ecosystem connectivity, methods, monitoring and assessment, permafrost change, winter ecology, anthropogenic development, and Indigenous Knowledge. Climate change emerged as the major driver among all categories and research questions. A key priority identified was the urgent need for long-term, harmonized monitoring programs among Arctic countries. Multiple knowledge gaps detected suggest that circumpolar research collaborations are required to tackle these issues.

Continuous permafrost zones are experiencing accelerated thaw due to Arctic warming, resulting in considerable greenhouse gas (GHG) emissions that significantly impact climate feedbacks. These permafrost thaw-induced landscape shifts promote the formation of thermokarst lakes, hotspots of biogeochemical activity, contaminant cycling and GHG production. Here, we present the first comprehensive assessment of dissolved organic matter (DOM) and terminal electron acceptors (TEAs) dynamics in two recently formed thermokarst lakes situated within tundra landscapes undergoing early peatland development driven by permafrost thaw in the Zackenberg valley, Northeastern Greenland. We conducted vertical profiles of physicochemical measurements, DOM properties, and TEAs throughout the water column, along with lake sediment characterization (delta 13C signature, FTIR characterization, C/N ratio). Additionally, a benthic flux chamber experiment was conducted to study biogeochemical differences at the sediment-water interface in both lakes. Analytical approaches included UV-visible and fluorescence spectroscopy, solid-phase extraction, FTIR spectroscopy, ICP-OES, isotope ratio mass spectrometer, and atomic absorption spectrometry. Our results reveal that the emerging lake showed higher molecular weight DOM and organic-rich sediments compared to the more mature thermokarst lake. Similarly, the younger lake exhibited stronger microbial activity in the sediment, with accentuated dissolved oxygen consumption nearly three times higher than the more mature lake, and a shift to reducing conditions after 30 min. Nevertheless, both lakes showed exceptionally high sediment oxygen demand, indicating strong benthic activity at both sites. As permafrost continues to thaw, the emergence and development of thermokarst lakes are likely to amplify greenhouse gas emissions in the Zackenberg valley. These findings represent a critical first step in understanding the shifting biogeochemical dynamics of lakes in a continuous permafrost region with high methane emissions.

As Arctic and Subarctic regions warm rapidly, thawing permafrost is releasing large amounts of dissolved organic matter (DOM) into forming and expanding thermokarst lakes. Lake functioning is strongly shaped by DOM quality and nutrient inputs, as well as site-specific environmental conditions. However, the effects of seasonality, lake morphometry, and ontogeny on biogeochemical mechanisms remain poorly characterized. We investigated three thermokarst lakes with contrasting ontogeny and morphometry in a degrading palsa-rich sporadic permafrost region. Sampling of water column, sediment porewater, lake sediments, and surrounding soils was conducted during summer and winter to analyze terminal electron acceptors (TEAs), DOM via UV-Visible and fluorescence spectroscopy, and sediments using delta 13C signatures and Fourier-transform infrared spectroscopy. Results reveal how a thermokarst lake's biogeochemistry is controlled by key factors: oxygen availability, substrate quality, and lake morphometry. Winter anoxia mobilized dissolved Fe and terrestrial DOM from sediments, while preserving protein-like FDOM and accumulating CO2 in the water column. Summer oxic conditions favor photochemical breakdown of large, recalcitrant structures, yielding smaller aromatic DOM. Lake ontogeny alters the quality of landscape inputs: the young lake showed signs of elevated sediment microbial processing and rapid oxygen depletion, driven by the thawing palsa; whereas the mature lake relies on photochemically produced aromatic DOM from older, recalcitrant soils. In conclusion, lake morphometry further modulates these processes by shaping mixing, stratification, and light exposure, emphasizing the importance of interacting physical and biogeochemical controls in structuring DOM cycling in thermokarst lakes.

On April 22, 2021, a large sensitive-clay landslide buried sediments of the Great Whale River (Nunavik, Canada) under millions of cubic metres of debris and liquefied postglacial clay, disrupting sediment geochemistry and benthic communities. In the summer of 2021, and at three subsequent time points over 28 months post-disturbance, we documented biogeochemical and ecological responses along a 12-km transect from the landslide origin to the river mouth at Hudson Bay, measuring major and trace elements in sediment cores, dissolved species in porewater, and benthic macroinvertebrate community composition. Within the first year, approximately 0.7 kg of Hg and 340 kg of Pb accumulated at the sediment surface across affected sites. Near the river mouth, dissolved porewater Fe and Mn increased up to 5-fold relative to upstream sites, coinciding with sediment Hg concentrations reaching 45.9 ng g-1 in deeper layers. By 11-16 months, these surface enrichments were leached or eroded downstream, indicating transient retention of landslide-derived trace elements. At 28 months, porewater Mn, Fe, sulfate and sulfide profiles exhibited redox zonation characteristic of reestablished diagenetic processes, coinciding with the reestablishment of a diverse benthic macroinvertebrate community. This study provides quantitative recovery timescales for a subarctic river system following landslide disturbance: <12 months for surface trace element export and 28 months for benthic recolonization. These recovery timescales are urgently needed as climate-driven increases in permafrost thaw and extreme precipitation intensify disturbance frequency across Arctic watersheds.

This study reports on the concentration of rare earth elements (REE) along with ancillary geochemical parameters at 11 locations across the Mackenzie River, its delta and coastal waters, both under ice and in open water. Specifically, we analyzed REE, carbon, and redox-sensitive elements (Fe, Mn) in 98 sediment samples and 96 porewater and overlying water samples collected under ice before the spring freshet (April-May) and in open water in early fall (August-September). While sediment REE concentrations remained relatively stable across seasons, results revealed a striking contrast between the two sampling seasons in the porewater, where REE concentrations were nearly two orders of magnitude higher under ice (avg. 216 nmolL-1) than under open water in the fall (avg. 3.20 nmolL-1). Similarly, dissolved organic carbon (DOC) concentrations were approximately one order of magnitude higher under ice than in the fall. Sediment REE concentrations were positively correlated to those of Fe and Mn, particularly under ice, consistent with control by adsorption processes onto their (oxy)hydroxides. In the porewater, winter and fall samples form distinct clusters based on concentration magnitudes. Chromophoric properties of dissolved organic matter (DOM) in the overlying water suggest that under-ice DOM was characterized by low aromaticity, older material compared to the more aromatic, humic-rich DOM measured in open water. We conclude that under-ice conditions, chiefly cold temperature, allow for DOM accumulation in the porewater, which, combined with other possible REE enrichment mechanisms in the porewater, such as REE-carbonate complex formation and exclusion during ice formation, contributes to the elevated winter REE concentrations observed here. To our knowledge, this is the first report of such large seasonal fluctuation in dissolved REE in the fluvial-marine transition zone of the Mackenzie, the largest riverine influence on the Arctic Ocean.

Lake metabolism is often quantified using continuous measures of dissolved oxygen (O2), where a 1: -1 stoichiometry with carbon dioxide (CO2) is assumed because of their roles in photosynthesis and respiration, respectively. However, many other physical, chemical, and biological processes decouple dissolved O2 and CO2 concentrations in lakes. Tracking departures from 1:-1 stoichiometry may provide insights into larger scale ecosystem functioning, particularly during fall when temperatures change and destratification occurs. Using continuous measures of both dissolved O2 and CO2 in a small temperate headwater lake, we looked at the interannual gas departure signals during fall over seven years. The beginning of fall, defined here as the start of leaf colour change, differed among years but coincided well with the onset of lake destratification and a shift in surface gas concentrations. Fall surface CO2 accumulation rates varied considerably, whereas O2 depletion rates were rather similar among years. Departure signals were broadly related to interannual differences in climate: more CO2 accumulated in the surface during the hottest-wettest fall compared to the coldest-driest one (0.81 and 0.37 µmol L-1 d-1, respectively), presumably from more catchment than hypolimnetic inputs. Lower CO2 accumulation occurred during years with prolonged hypolimnetic hypoxia potentially through enhanced CO2 consumption by methanogenesis. Other internal biological phenomena influenced fall departure signals, including a large metalimnetic oxygen peak, and higher fall surface primary production. We suggest gas departures during fall provide an integrative metabolic fingerprint for temperate stratified lakes, as well as insights into winter-priming conditions. Highlights ### Competing Interest Statement The authors have declared no competing interest.

We studied selenium (Se) sequestration in minimally disturbed lacustrine sediments using flow-through reactors (FTR) in response to organic matter lability, selenium (Se) speciation and temperature (4 and 23°C). Initial sediment was composed of either fresh or aged organic matter (OM), and was fed with environmentally relevant, low Se concentrations and filtered lake water. We monitored Se concentration as well as speciation along with pH and the concentrations of dissolved OM, NO3-, NO2-, Fe(II), SO42- and HS- in the outflow of FTRs during 8 experimental phases along increasing Se concentrations. All experiments sequestered a large proportion of Se. Fresh, labile OM removed 50% more Se than aged, more recalcitrant OM. Along with a highest proportion of reduced redox-sensitive species in the reactors with fresh OM, this result is consistent with reducing conditions promoting Se sequestration. Inflowing selenite was sequestered to a larger extent than inflowing selenate. Lastly, only selenate reduction responded strongly to temperature. At 100 nM inflow, selenate was sequestered at a rate of 92 pmol cm-3 d-1 at 23°C, which lowered to 80 pmol cm-3 d-1 at 4°C. Outflow Se speciation for selenate reduction experiments comprised mostly of organic Se species at 23°C and, in contrast, solely of selenate at 4°C. We hypothesize that selenate reduction proceeded via microbial processes, in line with reactions catalyzed by enzymes being temperature dependent. Overall, our findings suggest that the mobilisation and warming of the boreal and permafrost carbon pools may increase the capacity of aquatic environments to sequester Se, lowering its bioavailability.

Climate warming is likely to increase the physical connectivity of ecosystems with their surroundings. For Arctic lakes, increasing meltwater and precipitation may enhance the inputs of nutrients, organic matter and microorganisms from their catchments, and the increasingly ice-free, open-water conditions of the Arctic Ocean may favor increased inputs of marine aerosols, including microbiota. This study therefore aimed to determine how changing connectivity to terrestrial and marine habitats may affect the dispersal, sorting, and establishment of bacterial communities in a coastal High Arctic lake. Three habitats in this model system were sampled for ice, water, and snow: the lake, inflowing water tracks over permafrost soils, and an adjacent ice-dammed bay connected to the Arctic Ocean. Lake water chemistry confirmed the hydrological connection between the lake and terrestrial habitats, with the lake fed by terrestrial carbon sources via snow and groundwater run-off. Sequencing of 16S rDNA and rRNA showed evidence of a small marine and terrestrial influence on the lake, but few bacterial phylotypes were common to all three connected habitats. These results imply ongoing strong environmental filtering by habitat type, despite the apparent and potentially rising connectivity, and provide an example of bacterial resilience in a region of rapid climate change.

Rising temperatures are destabilizing permafrost in northern latitudes, leading to the mobilization, transformation and cycling of natural organic matter (NOM), nutrients, and contaminants into newly formed aquatic systems. Analyzing the chemical composition of organic matter is crucial for understanding the biogeochemical processes at play. Furthermore, it is essential to investigate how seasonal variations and anoxic conditions influence these processes, as well as their effects on microbial activity and NOM composition. This review provides an overview of northern peatlands, terminal electron acceptor species, and key analytical techniques used to characterize organic matter: UV/Vis and Fluorescence Spectroscopy, FTIR, FT-ICR-MS, and Nuclear Magnetic Resonance. Rather than focusing on the theoretical aspects of these techniques, we emphasize the type of information they offer about NOM and how to interpret these data within the context of biogeochemical transformations in permafrost-affected systems.

The Mackenzie River is North America's largest contributor of freshwater and sediment to the Arctic Ocean. Here, we evaluate the potential of rare earth elements (REE) as tracers of its sediment sources and fate, from the river mouth to the deep Arctic Ocean. We collected sediment cores from 21 sites, from the delta to the marine shelves, slopes and basins and measured the spatial and down-core distribution of total, leached and residual REE concentrations. Our results show that the proportion of leached REE is highest in the delta. This proportion decreases with distance from the river, suggesting mixing with other sediment sources, REE loss to the residual phase, or REE scavenging via adsorption and complexation in coastal waters. Normalized REE concentrations plotted against their atomic number provide regional signatures. The leached REE signatures indicate medium REE enrichment in the Mackenzie Delta, an enrichment that diminishes with distance from the delta. We then used a similarity index (SI) to investigate the divergence amongst REE signatures, with riverine and deep marine basin values as endmembers for the calculation. Our results highlight the influence of the Mackenzie Region sediments on the Beaufort Sea margin. Overall, our findings demonstrate that REE are relevant tracers for identifying sediment sources and that tracking REE distribution from the delta to the deep Arctic Ocean offers additional insights into sediment transport mechanisms.

Lake and river sediments play major roles in the biogeochemistry of inland water ecosystems. Materials are continuously exchanged across the sediment–water interface, but sediments are also long-term storage sites for organic carbon, biogenic silica, phosphorus, and pollutants. Chemical gradients in the interstitial waters of sediments reflect changes in microbial community structure and function with depth, in turn driven by the availability of electron acceptors. Four types of microbiomes (complete assemblages of microbes) are associated with sediment habitats: suspended in the water column as microbial aggregates; on lake bottoms and riverbeds as microbial biofilms; in the hyporheic zone beneath river beds; and as communities across redox gradients in the bottom sediments of lakes. Microbial breakdown of organic matter results in methane and carbon dioxide production, with large variations in decomposition rates and gas production across trophic states. Human activities are altering inland water ecosystems through wide-ranging effects on sediment processes, including via land-use impacts, dams, and climate warming.

We set out to study the seasonal variations in porewater phosphorus and lanthanum concentrations in the dated sediment cores from a small eutrophic lake that has been treated with Phoslock, a lanthanum-modified bentonite (LMB) amendment. Three sites were sampled when the hypolimnion was either oxygenated or anoxic: (i) the lake's deepest point, (ii) a littoral site receiving inflows from the catchment, and (iii) a littoral site influenced by nearby septic tanks. Phosphate (PO43--P), lanthanum (La), iron (Fe), dissolved organic carbon (DOC) and sulfate (SO42-) were measured in porewater samples. An inverse diagenetic model was used to quantify fluxes of dissolved elements across the sediment-water interface as well as the net rate of their reactions along the porewater concentration gradients. Results show that porewater P and Fe underwent strong seasonal dynamics, while La did not. P fluxes, 20-fold higher at the deepest site than elsewhere in the basin, were influenced by anoxic conditions in the hypolimnion during summer and winter, suggesting that P mobility remained sensitive to redox fluctuations despite the addition of La. At the deepest site, fluxes of P across the sediment-water interface increased from 1 to 9 x 10-9 mu mol cm-2 s-1 between spring and summer, while the rate of P production to the porewater also increased a hundredfold. These increases were concurrent with Fe mobilization. Finally, sediment dating shows that the fraction of P sequestered by La is buried under freshly deposited sediment at a rate of 2-3 mm per year. These results indicate that external P fluxes and erosion control remain crucial to maintain the longevity of the LMB treatment. Seasonal porewater dynamics in a lanthanum-remediated lake reveal that phosphorus mobility remains sensitive to redox conditions during its burial.

Environmental context Natural dissolved organic matter strongly influences the biogeochemistry and bioavailability of trace metals in natural waters. Chemical equilibrium models are often used to predict the relative importance of the free metal cation, a recognised indicator of the metal’s bioavailability. Here we show how the nature of the organic matter varies between two lakes, affecting the measured speciation of copper and nickel, a result that challenges existing chemical equilibrium models. Rationale Thermodynamic models such as the Windermere Humic Aqueous Model (WHAM) are often used to estimate the binding of cations by dissolved organic matter (DOM) in natural aquatic systems. Such models require as input data the quantity of DOM but do not consider its quality. Using two well-characterised lakewater samples, we demonstrate, for realistic environmental conditions, that the conditional binding parameters for the complexation of Ni and Cu with natural DOM vary between lakes and we relate these differences to the spectroscopic quality of the DOM. Methodology Waters from two lakes with contrasting types of DOM were titrated with Cu and Ni and the conditional binding parameters were calculated using a two-site ligand model, with associated conditional stability constants implemented in PHREEQC v.3.1.2, and compared between lakes and between metals. The titration curves for each lake were compared to those predicted by WHAM v7.05. Results Binding affinities and capacities of DOM for Cu and Ni were found to differ not only between metals, but also between lakes. Discussion Overall, the titration results suggest that the more aromatic humic-like DOM from allochthonous sources may have a significantly higher complexation affinity for Ni than the more protein-like DOM from autochthonous sources. The differing behaviour of Ni and Cu in the two lakes suggests that they are binding to different types of binding sites within the DOM matrix. More data with various natural DOM samples are needed to capture the diversity of metal–DOM interactions and to improve our ability to predict metal speciation in natural waters.

Lakes represent a vital source of freshwater, accounting for 87

Climate warming is accelerating the thawing of permafrost, which contains almost twice as much carbon as the atmosphere, to a point where a large quantity of dissolved organic matter (DOM) is being mobilized toward surface waters, including thermokarst ponds. DOM can be partially photodegraded into volatile organic compounds (VOCs), which are little studied in Arctic environments. The main objective of this work is to identify and quantify the VOCs emitted to the gas phase by photochemistry from thermokarst water sampled in four ponds from two study sites in northern Quebec. VOC emissions were characterized by proton-transfer reaction mass spectrometry. Results show rapid photoproduction of between 35 and 59 VOCs when DOM water samples are exposed to radiation. Our results also show that the quality of DOM is a more important factor to control VOC photoproduction than the quantity of DOM. Depending on the assumptions used in upscaling our laboratory results to the field sites, calculations yield net carbon fluxes between 1.93 and 174 mu mol C m(-2) d(-1). While these values are small compared to literature values of CO2 and CH4 fluxes from thermokarst ponds, this process represents an important flux of reactive molecules that could affect Arctic atmospheric chemistry. [GRAPHICS]

Northern regions are warming faster than the rest of the globe. It is difficult to predict ecosystem responses to warming because the thermal sensitivity of their biophysical components varies. Here, we present an analysis of the authors' expert judgment regarding the sensitivity of six ecosystem components - permafrost, peatlands, lakes, snowpack, vegetation, and endothermic vertebrates - across northern landscapes ranging from boreal to polar biomes. We identified 28 discontinuous component states across a 3700 km latitudinal gradient in northeastern North America and quantified sensitivity as the transition time from an initial to a contrasting state following a theoretical step change increase in mean annual air temperature of 5 degrees C. We infer that multiple interconnected state shifts are likely to occur within a narrow subarctic latitudinal band at timescales of 10 to more than 100 years, and response times decrease with latitude. Response times differ between components and across latitudes, which is likely to impair the integrity of ecosystems. Warming-induced changes in permafrost, peatlands, lakes, snowpack, vegetation, and vertebrates could impact northern ecosystem integrity, with different response times across components and latitude, according to an expert assessment of sensitivity in northern landscapes.

Arctic and subarctic landscapes have unique hydrological and limnological features and are now experiencing rapid change due to climate warming and permafrost thaw. The highly abundant lakes, ponds, and rivers across these landscapes play an increasingly important role in global biogeochemical cycles and are sentinels of environmental changes. However, studying these remote waters poses challenges for both in situ sampling and remote-sensing analysis. Here we developed a synergistic remote-sensing strategy that combined PlanetScope and Sentinel-2 satellite data to estimate limnicity (water fraction per land surface), limnodensity (density of water bodies), and limnodiversity (optical diversity of water bodies) along a boreal forest-tundra transect, from the non-permafrost to the continuous permafrost zones of western Nunavik (Subarctic Canada). Our analyses show that this region hosts 335,281 water bodies, around 90% in the 0.0001 to 0.01 km2 size range. In bedrock outcrops, large water bodies were mostly associated with glacially carved depressions (higher limnicity). In contrast, small water bodies were predominately found in sedimentary infills along valleys (higher limnodensity). The discontinuous permafrost zone had the highest limnodensity and limnodiversity. This was likely due to permafrost thaw (thermokarst), particularly the collapse, subsidence, and erosion of palsas (organic permafrost mounds), resulting in ponds with black- and brown-colored waters, and lithalsas (mineral permafrost mounds), resulting in ponds with brown, light-brown, and sometimes white-colored waters. Some of these limnodense and limnodiverse landscapes, although covering only 2 to 7% of the total area of the study region, contained over one-third (34%) of the total number of water bodies, 97% of which were <0.01 km2; they accounted for a small proportion of the total black-colored water bodies (23%), but a high proportion of the total brown- (60%) and light brown-colored water bodies (92%) throughout the region. This research underscores the utility of optical satellite remote sensing for assessing water body types and for evaluating their individual and distinct aquatic responses to climate change. The dataset may be used to improve the modeling of carbon fluxes by better categorizing small water bodies affected by organic or mineral soil type settings. This is an important factor dictating biogeochemical responses, with effects on albedo, climate feedbacks, and ecosystem dynamics in the boreal forest-tundra region. The framework developed here may be applied to landscapes elsewhere in the world that have high densities of water bodies of variable size and optical properties.

Thermokarst ponds (thaw lakes) are ubiquitous in northern landscapes. They are hotspots for the biogeochemical processing of elements, such as carbon (C), nitrogen (N), sulfur (S), iron (Fe) and manganese (Mn). In turn, those elementary cycles may control the mobility of selenium (Se), an essential micronutrient. To unravel these coupled biogeochemical cycles and identify processes controlling Se mobility, we studied four thermokarst ponds in a subarctic peatland valley influenced by permafrost thaw. The data set comprises of water column and sediment porewater concentration profiles collected during both summer and winter. Physicochemical parameters and dissolved concentrations of major elements, nutrients, and Se were measured and used to model fluxes at the sediment-water interface and to calculate Se speciation. The results suggest that the proximity of the pond from the permafrost structures influenced their biogeochemical dynamics. In the ponds close to permafrost, Se concentrations are 2-fold higher in winter compared to summer, accompanied by an increase in sediment fluxes from 13 to 149 pmol cm(-2) yr(-1) between summer and winter. The combination of comparatively older dissolved organic matter and of oxygenated conditions explain the seasonal variation in Se concentrations. In the ponds further from the permafrost, Se concentrations are higher, remain unchanged in the water column across seasons, and are linearly correlated with both DOC (R-2 = 0.64, p < 0.01, n = 50) and Fe (R-2 = 0.60) concentrations. Thermodynamic calculations show that Se(IV) dominates Se speciation in the porewater at all sites, while the water column reaches saturation with respect to elemental zerovalent Se, suggesting that precipitation of elemental Se could mediate dissolved Se concentrations. Collectively, our results point to the strong control that redox conditions exert on Se mobility, via DOC and Fe, and to the linkages between landscape features, pond physicochemistry, and Se dynamics.

Northern ecosystems are among the most exposed to warming and their responses are difficult to anticipate due to the variable sensitivity of their biophysical components. Using an analysis based on expert assessment, we investigated heterogeneity in the sensitivity to climate-driven state shifts across the vast northern landscape, from the boreal to the polar biomes. Over a 3,700 km latitudinal gradient in northeastern North America, we identified 28 discontinuous states for six ecosystem components: permafrost, peatlands, lakes, snowpack, vegetation, and endothermic vertebrates. Sensitivities were quantified by the estimated time required to shift from an initial to a contrasting state in response to a 5°C step increase in mean annual air temperature. The inferred scenario reveals that multiple interconnected state shifts are likely to occur within a narrow subarctic latitudinal band at timescales of 10 to >100 years. However, response times decrease with latitude, with freshwater systems at high latitudes displaying heightened susceptibility to rapid state shifts (timescales of 1 to 10 years). The lack of coherence in response times between components and across latitudes will likely impair the integrity of northern ecosystems and generate heterogeneous range shifts, resulting in the reconfiguration of landscapes and ecosystems.

Polar amplification of climate change has the potential to cause large‐scale shifts in the dissolved oxygen (DO) dynamics of Arctic lakes, with implications for fish survival, greenhouse gas production, and drinking water quality. While DO is also a sentinel of environmental changes of physical, chemical, and biological nature (e.g., ice cover, temperature, dissolved organic carbon, photosynthesis, and respiration), no synthesis exists of current knowledge of DO dynamics across the diverse freshwater systems of the Arctic. We thus conducted a systematic review of the literature that yielded DO data from 167 sites north of the Subarctic limit (based on vegetation zones), spanning 76 years and including 40 sites with time series. The compilation revealed insufficient observations for adequate representativeness of oxygen dynamics over Arctic ecosystem gradients. We described the main processes controlling DO budgets of Arctic lakes and tested relationships of summer oxygen depletion with maximum depth and latitude. The meta‐analysis showed that most sites with low O2 concentrations were shallow (<10 m) and situated toward the southern end of the latitudinal gradient. Permanently stratified lakes with deep, perennially anoxic basins were located toward the northern end of the gradient. By way of a conceptual model, we identified the direct and indirect drivers and mechanisms that lead to changes in oxygen budgets in the context of the warming Arctic. This comprehensive update on available data allowed us to suggest future research directions and recommend the use of moored instruments for continuous all‐season observations, combined with modeling, remote sensing, and paleo‐reconstructions.