Search

Anthropogenic warming in the Arctic is causing hydrological cycle intensification and permafrost thaw, with implications for flows of water, carbon, and energy from terrestrial biomes to coastal zones. To better understand the likely impacts of these changes, we used a hydrology model driven by meteorological data from atmospheric reanalysis and two global climate models for the period 1980–2100. The hydrology model accounts for soil freeze–thaw processes and was applied across the pan-Arctic drainage basin. The simulations point to greater changes over northernmost areas of the basin underlain by permafrost and to the western Arctic. An acceleration of simulated river discharge over the recent past is commensurate with trends drawn from observations and reported in other studies. Between early-century (2000–2019) and late-century (2080–2099) periods, the model simulations indicate an increase in annual total runoff of 17 %–25 %, while the proportion of runoff emanating from subsurface pathways is projected to increase by 13 %–30 %, with the largest changes noted in summer and autumn and across areas with permafrost. Most notably, runoff contributions to river discharge shift to northern parts of the Arctic Basin that contain greater amounts of soil carbon. Each season sees an increase in subsurface runoff; spring is the only season where surface runoff dominates the rise in total runoff, and summer experiences a decline in total runoff despite an increase in the subsurface component. The greater changes that are seen in areas where permafrost exists support the notion that increased soil thaw is shifting hydrological contributions to more subsurface flow. The manifestations of warming, hydrological cycle intensification, and permafrost thaw will impact Arctic terrestrial and coastal environments through altered river flows and the materials they transport. [ABSTRACT FROM AUTHOR]

Landscapes are often assumed to be homogeneous when interpreting eddy covariance fluxes, which can lead to biases when gap-filling and scaling up observations to determine regional carbon budgets. Tundra ecosystems are heterogeneous at multiple scales. Plant functional types, soil moisture, thaw depth, and microtopography, for example, vary across the landscape and influence net ecosystem exchange (NEE) of carbon dioxide (CO2) and methane (CH4) fluxes. With warming temperatures, Arctic ecosystems are changing from a net sink to a net source of carbon to the atmosphere in some locations, but the Arctic's carbon balance remains highly uncertain. In this study we report results from growing season NEE and CH4 fluxes from an eddy covariance tower in the Yukon–Kuskokwim Delta in Alaska. We used footprint models and Bayesian Markov chain Monte Carlo (MCMC) methods to unmix eddy covariance observations into constituent land-cover fluxes based on high-resolution land-cover maps of the region. We compared three types of footprint models and used two land-cover maps with varying complexity to determine the effects of these choices on derived ecosystem fluxes. We used artificially created gaps of withheld observations to compare gap-filling performance using our derived land-cover-specific fluxes and traditional gap-filling methods that assume homogeneous landscapes. We also compared resulting regional carbon budgets when scaling up observations using heterogeneous and homogeneous approaches. Traditional gap-filling methods performed worse at predicting artificially withheld gaps in NEE than those that accounted for heterogeneous landscapes, while there were only slight differences between footprint models and land-cover maps. We identified and quantified hot spots of carbon fluxes in the landscape (e.g., late growing season emissions from wetlands and small ponds). We resolved distinct seasonality in tundra growing season NEE fluxes. Scaling while assuming a homogeneous landscape overestimated the growing season CO2 sink by a factor of 2 and underestimated CH4 emissions by a factor of 2 when compared to scaling with any method that accounts for landscape heterogeneity. We show how Bayesian MCMC, analytical footprint models, and high-resolution land-cover maps can be leveraged to derive detailed land-cover carbon fluxes from eddy covariance time series. These results demonstrate the importance of landscape heterogeneity when scaling carbon emissions across the Arctic. [ABSTRACT FROM AUTHOR]

The long‐term absorption by the oceans of atmospheric carbon dioxide is leading to the slow decline of ocean pH, a process termed ocean acidification (OA). The Arctic is a challenging region to gather enough data to examine the changes in carbonate chemistry over sufficient scales. However, algorithms that calculate carbonate chemistry parameters from more frequently measured parameters, such as temperature and salinity, can be used to fill in data gaps. Here, these published algorithms were evaluated against in situ measurements using different data input types (data from satellites or in situ re‐analysis climatologies) across the Arctic Ocean. With the lowest uncertainties in the Atlantic influenced Seas (AiS), where re‐analysis inputs achieved total alkalinity estimates with Root Mean Squared Deviation (RMSD) of 21 μmol kg−1 and a bias of 2 μmol kg−1 (n = 162) and dissolved inorganic carbon RMSD of 24 μmol kg−1 and bias of −14 μmol kg−1 (n = 262). AiS results using satellite observation inputs show similar bias but larger RMSD, although due to the shorter time span of available satellite observations, more contemporary in situ data would provide further assessment and improvement. Synoptic‐scale observations of surface water carbonate conditions in the Arctic are now possible to monitor OA, but targeted in situ data collection is needed to enable the full exploitation of satellite observation‐based approaches. Plain Language Summary: The long‐term absorption by the oceans of atmospheric carbon dioxide is leading to the slow decline of ocean pH, a process termed ocean acidification (OA). Sea surface salinity and temperature measurements from satellites or in situ re‐analysis products can be used as input to empirical algorithms to calculate OA parameters. This paper provides a first analysis of published Arctic Ocean empirical algorithms to estimate surface water OA parameters using observation‐based data sets. Results show promise in the Atlantic influenced Seas using both in situ re‐analysis and satellite products, but satellite salinity is relatively recent, and a paucity of in situ data in the satellite salinity era precludes a robust assessment. To fully exploit satellite‐based approaches, efforts need to focus on collecting in situ data while these satellites are overhead and operating in orbit. Key Points: Observation‐based data sets enable synoptic spatio‐temporal assessments of Arctic Ocean carbonate system parametersRe‐analysis and satellite products predict total alkalinity with accuracies of ∼21 μmol kg−1Targeted in situ data collection is needed to fully exploit satellite observations in the Arctic to enable carbonate system monitoring [ABSTRACT FROM AUTHOR]

Arctic and Subarctic environments are among the most vulnerable regions to climate change. Increases in liquid precipitation and changes in snowmelt onset are cited as the main drivers of change in streamflow and water temperature patterns in some of the largest rivers of the Canadian Arctic. However, in spite of this evidence, there is still a lack of research on water temperature, particularly in the eastern Canadian Arctic. In this paper, we use the CEQUEAU hydrological‐water temperature model to derive consistent long‐term daily flow and stream temperature time series in Aux Mélèzes River, a non‐regulated basin (41 297 km2) in the eastern Canadian subarctic. The model was forced using reanalysis data from the fifth‐generation ECMWF atmospheric reanalyses (ERA5) from 1979 to 2020. We used water temperature derived from thermal infrared (TIR) images as reference data to calibrate CEQUEAU's water temperature model, with calibration performed using single‐site, multi‐site, and upscaling factors approaches. Our results indicate that the CEQUEAU model can simulate streamflow patterns in the river and shows excellent spatiotemporal performance with Kling‐Gupta Efficiency (KGE) metric >0.8. Using the best‐performing flow simulation as one of the inputs allowed us to produce synthetic daily water temperature time series throughout the basin, with the multi‐site calibration approach being the most accurate with root mean square errors (RMSE) <2.0°C. The validation of the water temperature simulations with a three‐year in situ data logger dataset yielded an RMSE = 1.38°C for the summer temperatures, highlighting the robustness of the calibrated parameters and the chosen calibration strategy. This research demonstrates the reliability of TIR imagery and ERA5 as sources of model calibration data in data‐sparse environments and underlines the CEQUEAU model as an assessment tool, opening the door to its use to assess climate change impact on the arctic regions of Canada. [ABSTRACT FROM AUTHOR]

The Arctic is experiencing rapid climate change, and the effect on hydrologic processes and resulting geomorphic changes to hillslopes and channels is unclear because we lack quantitative models and theory for rapid changes resulting from thawing permafrost. The presence of permafrost modulates water flow and the stability of soil‐mantled slopes, implying that there should be a signature of permafrost processes, including warming‐driven disturbance, in channel network extent. To inform understanding of hillslope‐channel dynamics under changing climates, we examined soil‐mantled hillslopes within a ∼300 km2 area of the Seward Peninsula, western Alaska, where discontinuous permafrost is particularly susceptible to thaw and rapid landscape change. In this study, we pair high‐resolution topographic and satellite data to multi‐annual observations of InSAR‐derived surface displacement over a 5‐year period to quantify spatial variations in topographic change across an upland landscape. We find that neither the basin slope nor the presence of knickzones controls the magnitude of recent surface displacements within the study basin, as may be expected under conceptual models of temperate hillslope evolution. Rather, the highest displacement magnitudes tended to occur at the broad hillslope‐channel transition zone. In this study area, this zone is occupied by water tracks, which are zero‐order ecogeomorphic features that concentrate surface and subsurface flow paths. Our results suggest that water tracks, which appear to occupy hillslope positions between saturation and incision thresholds, are vulnerable to warming‐induced subsidence and incision. We hypothesize that gullying within water tracks will outpace infilling by hillslope processes, resulting in the growth of the channel network under future warming. Plain Language Summary: Climate and ecology can shape hillslopes and the extent of river networks by controlling how much water is available for erosion. These forces also control whether water can erode soil if it is strengthened by ice or roots. The permeability and stability of permafrost hillslopes change with seasonal and long‐term warming due to frozen ground's impermeability and resistance to erosion. This link between temperature and erosion in permafrost landscapes is thus more direct than most geomorphic models developed at lower latitudes presume. We related the locations of satellite topographic change to the geomorphic processes that dominate that part of the landscape based on the shape of the hillslopes and valleys. This allows us to determine whether the pattern of disturbance across the landscape is related to geomorphic variables such as slope or climate‐modulated variables such as soil saturation. Topographic change primarily occurs in saturated areas at the tips of the river network. At these locations, features called "water tracks" form the transition between hillslopes and river valleys. Changes in climate and vegetation in permafrost landscapes are potentially driving water tracks to transition into true channels, expanding the channel network. Key Points: Seasonal and long‐term permafrost thaw change hillslope hydrology and erodibilitySatellites observe surface displacements concentrated at the transition between hillslopes and channelsA conceptual model is proposed for hillslope‐channel transitions in permafrost landscapes mediated by water tracks [ABSTRACT FROM AUTHOR]

Landscapes are often assumed to be homogeneous when interpreting eddy covariance fluxes, which can lead to biases when gap-filling and scaling-up observations to determine regional carbon budgets. Tundra ecosystems are heterogeneous at multiple scales, with variation in plant functional types, soil moisture, thaw depth, and microtopography, for example, influencing net ecosystem exchange (NEE) of carbon dioxide (CO2) and methane (CH4) fluxes. With warming temperatures, Arctic ecosystems could change from a net sink to a net source of carbon to the atmosphere in some locations, but the carbon balance remains highly uncertain. In this study we report results from growing season NEE and CH4 fluxes from an eddy covariance tower in the Yukon-Kuskokwim Delta in Alaska. We used footprint models and Bayesian Markov Chain Monte Carlo (MCMC) methods to un-mix tower observations into constituent landcover fluxes based on high resolution landcover maps of the tower region. We compared three types of footprint models and used two landcover maps with varying complexity to determine the effects of these choices on derived ecosystem fluxes. We used artificially created gaps of withheld observations to compare gap-filling performance using our derived landcover-specific fluxes and traditional gap-filling methods that assume homogeneous landscapes. We also compared resulting regional carbon budgets when scaling-up observations using heterogeneous and homogeneous approaches. Traditional gap-filling methods performed worse at predicting artificially withheld gaps in NEE than those that accounted for heterogeneous landscapes, while there were only slight differences between footprint models and landcover maps. We identified and quantified hot spots of carbon fluxes in the landscape (e.g., late growing season emissions from wetlands and small ponds). We resolved distinct seasonality in tundra growing season NEE fluxes. Scaling while assuming a homogeneous landscape overestimated the growing season CO2 sink by a factor of two and underestimated CH4 emissions by a factor of two when compared to scaling with any method that accounts for landscape heterogeneity. We show how Bayesian MCMC, analytical footprint models, and high resolution landcover maps can be leveraged to derive detailed landcover carbon fluxes from eddy covariance timeseries. These results demonstrate the importance of landscape heterogeneity when scaling carbon emissions across the Arctic. [ABSTRACT FROM AUTHOR]

Permafrost thaw is hypothesized to increase riverbank erosion rates, which threatens Arctic communities and infrastructure. However, existing erosion models have not been tested against controlled flume experiments with open‐channel flow past an erodible, hydraulically rough permafrost bank. We conducted temperature‐controlled flume experiments where turbulent water eroded laterally into riverbanks consisting of sand and pore ice. The experiments were designed to produce ablation‐limited erosion such that any thawed sediment was quickly transported away from the bank. Bank erosion rates increased linearly with water temperature, decreased with pore ice content, and were insensitive to changes in bank temperature, consistent with theory. However, erosion rates were approximately a factor of three greater than expected. The heightened erosion rates were due to a greater coefficient of heat transfer from the turbulent water to the permafrost bank caused by bank grain roughness. A revised ablation‐limited bank erosion model with a heat transfer coefficient that includes bank roughness matched our experimental results well. Results indicate that bank erosion along Arctic rivers can accelerate under scenarios of warming river water temperatures for cases where the cadence of bank erosion is set by pore‐ice melting rather than sediment entrainment. Plain Language Summary: Many rivers in the Arctic have banks made up of permanently frozen sand and ice (permafrost) that are susceptible to erosion when they thaw. To understand how bank erosion may change as the Arctic climate warms, we conducted laboratory experiments using a channel with an erodible frozen bank. We found that warmer river water and lower bank‐ice content produced faster erosion rates. In contrast, bank erosion was insensitive to the ground temperature. Bank erosion rates were three‐fold faster than predicted by existing theory. We attribute the faster‐than‐expected erosion to a greater transfer of heat from the river water due to bank roughness. Our results imply that warming river water may increase riverbank erosion rates in permafrost regions, threatening communities and infrastructure built along Arctic rivers. Key Points: Flume experiments with frozen, erodible riverbanks were used to test and revise theoryErosion rates were affected by hydrodynamically rough banks that change the rate of heat transferAblation‐limited bank erosion rates increase with warmer water and lower pore‐ice content and are insensitive to bank temperature [ABSTRACT FROM AUTHOR]

Climate change is creating widespread ecosystem disturbance across the permafrost zone, including a rapid increase in the extent and severity of tundra wildfire. The expansion of this previously rare disturbance has unknown consequences for lateral nutrient flux from terrestrial to aquatic environments. Lateral loss of nutrients could reduce carbon uptake and slow recovery of already nutrient-limited tundra ecosystems. To investigate the effects of tundra wildfire on lateral nutrient export, we analyzed water chemistry in and around the 10-year-old  Anaktuvuk River fire scar in northern Alaska. We collected water samples from 21 burned and 21 unburned watersheds during snowmelt, at peak growing season, and after plant senescence in 2017 and 2018. After a decade of ecosystem recovery, aboveground biomass had recovered in burned watersheds, but overall carbon and nitrogen remained ~20% lower, and the active layer remained ~10% deeper. Despite lower organic matter stocks, dissolved organic nutrients were substantially elevated in burned watersheds, with higher flow-weighted concentrations of organic carbon (25% higher), organic nitrogen (59% higher), organic phosphorus (65% higher), and organic sulfur (47% higher). Geochemical proxies indicated greater interaction with mineral soils in watersheds with surface subsidence, but optical analysis and isotopes suggested that recent plant growth, not mineral soil, was the main source of organic nutrients in burned watersheds. Burned and unburned watersheds had similar δ 15 N-NO 3 - , indicating that exported nitrogen was of preburn origin (i.e., not recently fixed). Lateral nitrogen flux from burned watersheds was 2- to 10-fold higher than rates of background nitrogen fixation and atmospheric deposition estimated in this area. These findings indicate that wildfire in Arctic tundra can destabilize nitrogen, phosphorus, and sulfur previously stored in permafrost via plant uptake and leaching. This plant-mediated nutrient loss could exacerbate terrestrial nutrient limitation after disturbance or serve as an important nutrient release mechanism during succession., (© 2021 John Wiley & Sons Ltd.)

Whether permafrost systematically alters the rate of riverbank erosion is a fundamental geomorphic question with significant importance to infrastructure, water quality, and biogeochemistry of high‐latitude watersheds. For over four decades, this question has remained unanswered due to a lack of data. Using remotely sensed imagery, we addressed this knowledge gap by quantifying riverbank erosion rates across the Arctic and subarctic. To compare these rates to non‐permafrost rivers, we assembled a global data set of published riverbank erosion rates. We found that erosion rates in rivers influenced by permafrost are on average nine times lower than non‐permafrost systems; erosion rate differences increase up to 40 times for the largest rivers. To test alternative hypotheses for the observed erosion rate difference, we examined differences in total water yield and erosional efficiency between these rivers and non‐permafrost rivers. Neither of these factors nor differences in river sediment loads provided compelling alternative explanations, leading us to conclude that permafrost limits riverbank erosion rates. This conclusion was supported by field investigations of rates and patterns of erosion along three rivers flowing through discontinuous permafrost in Alaska. Our results show that permafrost limits maximum bank erosion rates on rivers with stream powers greater than 900 Wm−1. On smaller rivers, however, hydrology rather than thaw rate may be the dominant control on bank erosion. Our findings suggest that Arctic warming and hydrological changes should increase bank erosion rates on large rivers but may reduce rates on rivers with drainage areas less than a few thousand km2. Plain Language Summary: The rate rivers erode their banks controls the pace of migration and the impacts on neighboring communities and ecosystems. Erosion of floodplains releases sediment, carbon, and other constituents into rivers affecting the biogeochemistry of rivers and ultimately the coastal oceans into which rivers flow. Across the Arctic, rivers erode through floodplains frozen continuously for more than 2 years (permafrost). Before ice‐bounded sediments can be eroded by flowing water, they must be thawed. Using aerial photographs, satellite imagery, and direct field observations, we found that permafrost slows the rate rivers erode their banks relative to rivers without permafrost. The effect of permafrost, however, varies with the size of the river and the erosion rates of large rivers are disproportionately slowed by permafrost. As a result, permafrost thaw due to climate change will likely increase erosion rates on large rivers and have limited impact on small rivers, but very little data are available for small rivers in the Arctic, highlighting key data need. Key Points: Permafrost systematically reduces riverbank erosion rates by up to nine times compared to rivers not in permafrost regionsThe influence of permafrost on small rivers is limited and increases with river sizePermafrost thaw due to climate change will likely increase erosion rates on large rivers and have a limited impact on smaller rivers [ABSTRACT FROM AUTHOR]

Climatic warming and permafrost thaw are predicted to increase Arctic riverbank erosion, threatening communities and accelerating sediment, carbon and nutrient cycling between rivers and floodplains. Existing theory assumes that pore‐ice thaw sets riverbank erosion rates, but overpredicts observed erosion rates by orders of magnitude. Here, we developed a simple model that predicts more modest rates due to a sediment‐entrainment limitation and riverbank armoring by slump blocks. Results show that during times of thaw‐limited erosion, the river rapidly erodes permafrost and undercuts its banks, consistent with previous work. However, overhanging banks generate slump blocks that must thaw and erode by sediment entrainment. Sediment entrainment can limit bank and slump block erosion rates, producing seasonally averaged rates more consistent with observations. Importantly, entrainment‐limited riverbank erosion does not depend on water temperature, indicating that decadal erosion rates may be less sensitive to warming than predicted previously. Plain Language Summary: Riverbank erosion in the Arctic is a major hazard for riverside communities and infrastructure. Arctic rivers flow through regions of permanently frozen ground, and this ground is thawing as the climate warms. Therefore, there is major concern that riverbank erosion will accelerate in the future because the ground loses its strength when thawed. However, in order for a riverbank to erode, the river must satisfy two conditions: it must thaw the frozen ground and entrain the thawed sand and mud. Our model and analyses suggest that riverbank erosion in many Arctic rivers can be limited by the river's ability to entrain and transport the sand and mud, rather than the canonical view that erosion is limited by the rate of ground thaw. Applying our model to the Yukon River indicates that thaw rates are so fast that they cannot set the rate of erosion for the melt season. Instead, bank erosion for part of the time is controlled by the ability of the river to move the bank sediment, making riverbank erosion less sensitive to warming river waters. Key Points: A new model shows that permafrost bank erosion depends both on pore ice thaw and sediment entrainmentSediment entrainment from thawed banks and slump blocks can be rate‐limiting in some cases, which helps explain slow bank migration ratesWhere limited by sediment entrainment, decadal erosion rates may be less sensitive to warming river water than predicted previously [ABSTRACT FROM AUTHOR]

Rising temperatures and an acceleration of the hydrological cycle due to climate change are increasing river discharge, causing permafrost thaw, glacial melt, and a shift to a groundwater‐dominated system in the Arctic. These changes are funneled to coastal regions of the Arctic Ocean where the implications for the distributions of nutrients and biogeochemical constituents are unclear. In this study, we investigate the impact of terrestrial runoff on marine biogeochemistry in Inuit Nunangat (the Canadian Arctic Archipelago)—a key pathway for transport and modification of waters from the Arctic Ocean to the North Atlantic—using sensitivity experiments from 2002 to 2020 with an ocean model of manganese (Mn). The micronutrient Mn traces terrestrial runoff and the modification of geochemical constituents of runoff during transit. The heterogeneity in Arctic runoff composition creates distinct terrestrial fingerprints of influence in the ocean: continental runoff influences Mn in the southwestern Archipelago, glacial runoff dominates the northeast, and their influence co‐occurs in central Parry Channel. Glacial runoff carries micronutrients southward from Nares Strait in the late summer and may help support longer phytoplankton blooms in the Pikialasorsuaq polynya. Enhanced glacial runoff may increase micronutrients delivered downstream to Baffin Bay, accounting for up to 18% of dissolved Mn fluxes seasonally and 6% annually. These findings highlight how climate induced changes to terrestrial runoff may impact the geochemical composition of the marine environment, and will help to predict the extent of these impacts from ongoing alterations of the Arctic hydrological cycle. Plain Language Summary: In the Arctic, climate change is expected to increase river flow and alter the composition of river water through permafrost thaw and glacial melt. Many rivers and land areas drain to the coastal Arctic Ocean; the impact of changes to the nutrients carried by river water to these regions are unclear. In this study, we focus on Inuit Nunangat (the Canadian Arctic Archipelago)—a series of shallow channels that connects the Arctic Ocean to the North Atlantic—and look at where in the ocean the material in the river water ends up and how much of the material travels downstream. We use experiments with an ocean model from 2002 to 2020 and track an element found in river water: manganese (Mn), which is also an important nutrient in the ocean. While continental rivers mainly influence Mn in the southwestern Archipelago, glaciers influence the northeastern Archipelago and supply nutrients to Pikialasorsuaq, one of the Arctic's most biologically active areas. Glaciers can contribute up to 18% to Mn transported downstream of Nares Strait seasonally and 6% yearly. Our findings highlight how climate related changes in the composition of river water impact the marine system of Inuit Nunangat and how these changes can funnel downstream. Key Points: The heterogeneity in Arctic drainage basins creates a north‐south separation in Mn contributions to the Canadian Arctic Archipelago oceanGlacial runoff from Nares Strait supplies micronutrients such as Mn to the Pikialasorsuaq or North Water polynyaChanges in glacial runoff composition in the Canadian Arctic Archipelago and northwestern Greenland are conveyed downstream into Baffin Bay [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Lakes are dominant features of the Arctic landscape, and they have great cultural and environmental significance. The amplified effects of global warming observed in the Arctic represent a threat to the integrity of these systems. Levels of dissolved oxygen (DO) in lake water have implications for fish survival, greenhouse gas production, and drinking water quality. To summarize the state of knowledge about DO in Arctic lakes, we reviewed literature and extracted data from 167 sites. We describe the main processes known to control the oxygen balance and classified the lakes according to their bottom oxygen concentrations during summer. Most lakes that had low oxygen were shallow and situated toward the southern part of our study region. Lakes that never mix, and thus preserve permanent oxygen depletion in their deep waters, were located toward the northern end of the gradient. With a conceptual model, we illustrate how climate change is likely to influence oxygen balance by the way of direct and indirect drivers. We suggest future research directions including the collection of continuous data throughout all seasons, modeling, remote sensing, and studies of sediment cores to reconstruct past conditions. Key Points: Our systematic review located oxygen data in the Arctic from 167 field sites spanning 76 years, including 40 lakes with time‐seriesMeta‐analysis showed that summer oxygen depletion occurred mostly in shallow lakes toward the southern end of the latitudinal gradientWe formulated conceptual models of oxygen sinks and sources relevant to Arctic lakes and their responses to ongoing climate change [ABSTRACT FROM AUTHOR]

Estimates of nitrate loading to the Arctic Ocean are limited by the lack of field observations within deltas partly due to logistical constraints. To overcome this limitation, we use a remote sensing framework to estimate retention of nitrate in Arctic deltas. We achieve this by coupling hydrological and biogeochemical process models at the network scale for five major Arctic deltas. Binary masks of delta channels were used to simulate flow direction and magnitude through networks. Models were parameterized using historical and seasonal observations. Simulated nitrate retention ranged from 2.9% to 15% of the incoming load. Retention rates were largest during winter but smallest during spring conditions when increased discharges export large nitrate masses to the coast. Under future climate scenarios, retention rates fall by ∼1%–10%. Arctic deltas have an important effect on the magnitude of nitrate entering Arctic seas and the inclusion of processing in deltas can improve flux estimates. Plain Language Summary: The Arctic Ocean is the smallest and shallowest of the world's oceans but receives the largest riverine input per basin volume. Thus, the flux of nitrate from land to sea through rivers in the circumpolar Arctic can have large impacts on coastal life and global biogeochemical cycles. To assess the impact of terrestrially derived nitrate on Arctic Ocean chemistry under current and future scenarios, accurate accounting of nitrate loading is needed. Deltas act as filters that reduce nitrate loads, but current estimates of flux exclude the effects of Arctic deltas on nitrate export. We use a novel approach based on satellite imagery to estimate the potential impact of deltas on nitrate retention on five Arctic deltas, representing a range of morphologies and sizes. Our analysis shows seasonal and morphological differences in nitrate processing rates in each delta with retention rates ranging from 2.9% to 15% of incoming load and most retention occurring during winter months. Under future climate scenarios, the efficiency of nitrate retention decreases by up to 10%. Our models suggest that Arctic deltas alter the magnitude of nitrate entering the ocean and future predictions of loading or current earth system models could be improved by incorporating their effect. Key Points: Remotely sensed data provide a useful tool for revealing patterns of nitrate retention in Arctic deltasChannel networks of Arctic deltas are most efficient at retaining nitrate during spring and winterHotspots of nitrate removal cluster according to network structure and discharge on Arctic deltas [ABSTRACT FROM AUTHOR]

Climate warming and related drivers of soil thermal change in the Arctic are expected to modify the distribution and dynamics of carbon contained in perennially frozen grounds. Thawing of permafrost in the Mackenzie River watershed of northwestern Canada, coupled with increases in river discharge and coastal erosion, triggers the release of terrestrial organic matter (OMt) from the largest Arctic drainage basin in North America into the Arctic Ocean. While this process is ongoing and its rate is accelerating, the fate of the newly mobilized organic matter as it transits from the watershed through the delta and into the marine system remains poorly understood. In the framework of the European Horizon 2020 Nunataryuk programme, and as part of the Work Package 4 (WP4) Coastal Waters theme, four field expeditions were conducted in the Mackenzie Delta region and southern Beaufort Sea from April to September 2019. The temporal sampling design allowed the survey of ambient conditions in the coastal waters under full ice cover prior to the spring freshet, during ice breakup in summer, and anterior to the freeze-up period in fall. To capture the fluvial–marine transition zone, and with distinct challenges related to shallow waters and changing seasonal and meteorological conditions, the field sampling was conducted in close partnership with members of the communities of Aklavik, Inuvik and Tuktoyaktuk, using several platforms, namely helicopters, snowmobiles, and small boats. Water column profiles of physical and optical variables were measured in situ, while surface water, groundwater, and sediment samples were collected and preserved for the determination of the composition and sources of OMt, including particulate and dissolved organic carbon (POC and DOC), and colored dissolved organic matter (CDOM), as well as a suite of physical, chemical, and biological variables. Here we present an overview of the standardized datasets, including hydrographic profiles, remote sensing reflectance, temperature and salinity, particle absorption, nutrients, dissolved organic carbon, particulate organic carbon, particulate organic nitrogen, CDOM absorption, fluorescent dissolved organic matter intensity, suspended particulate matter, total particulate carbon, total particulate nitrogen, stable water isotopes, radon in water, bacterial abundance, and a string of phytoplankton pigments including total chlorophyll. Datasets and related metadata can be found in (10.1594/PANGAEA.937587). [ABSTRACT FROM AUTHOR]

Arctic river deltas define the interface between the terrestrial Arctic and the Arctic Ocean. They are the site of sediment, nutrient, and soil organic carbon discharge to the Arctic Ocean. Arctic deltas are unique globally because they are underlain by permafrost and acted on by river and sea ice, and many are surrounded by a broad shallow ramp. Such ramps may buffer the delta from waves, but as the climate warms and permafrost thaws, the evolution of Arctic deltas will likely take a different course, with implications for both the local scale and the wider Arctic Ocean. One important way to understand and predict the evolution of Arctic deltas is through numerical models. Here we present ArcDelRCM.jl, an improved reduced-complexity model (RCM) of arctic delta evolution based on the DeltaRCM-Arctic model , which we have reconstructed in Julia language using published information. Unlike previous models, ArcDelRCM.jl is able to replicate the ramp around the delta. We have found that the delayed breakup of the so-called "bottom-fast ice" (i.e. ice that is in direct contact with the bed of the channel or the sea, also known as "bed-fast ice") on and around the deltas is ultimately responsible for the appearance of the ramp feature in our models. However, changes made to the modelling of permafrost erosion and the protective effects of bottom-fast ice are also important contributors. Graph analyses of the delta network performed on ensemble runs show that deltas produced by ArcDelRCM.jl have more interconnected channels and contain less abandoned subnetworks. This may suggest a more even feeding of sediments to all sections of the delta shoreline, supporting ramp growth. Moreover, we showed that the morphodynamic processes during the summer months remain active enough to contribute significant sediment input to the growth and evolution of Arctic deltas and thus should not be neglected in simulations gauging the multi-year evolution of delta features. Finally, we tested a strong climate-warming scenario on the simulated deltas of ArcDelRCM.jl, with temperature, discharge, and ice conditions consistent with RCP7–8.5. We found that the ramp features degrade on the timescale of centuries and effectively disappear in under 1 millennium. Ocean processes, which are not included in these models, may further shorten the timescale. With the degradation of the ramps, any dissipative effects on wave energy they offered would also decrease. This could expose the sub-aerial parts of the deltas to increased coastal erosion, thus impacting permafrost degradation, nutrients, and carbon releases. [ABSTRACT FROM AUTHOR]

In cold alpine areas, the hydrological control on dissolved organic matter (DOM) export in relation to permafrost distribution remains uncertain on a catchment scale. To address this, the seasonal variations in DOM chemical features of groundwater and stream water were examined from 2013 to 2019 in a representative catchment on the northeastern Qinghai–Tibet Plateau, which is covered by both permafrost (at elevations higher than 3,500 m a.s.l.) and seasonally frozen areas. The results show that the highest dissolved organic carbon (DOC) concentration occurred during the thawing period (April–May), while the highest DOC flux occurred during the thawed period (June–early October). In the permafrost area, the freeze–thaw process significantly influenced the groundwater flow paths and DOM. During the thawing period, with shallow groundwater flow path through the organic soil layer, the stream water DOM recharged by suprapermafrost groundwater was characterized by high aromaticity and high DOC concentrations. During the thawed period, the deepening groundwater flow path through the mineral layer and dilution by overland flow, resulted in low DOC concentrations and DOM with lower aromaticity in stream water. When groundwater flowed from the permafrost area into the porous aquifers in the seasonally frozen area, the groundwater flow path also affected DOM dynamics. The stream water at the catchment outlet, which received groundwater discharge from the porous aquifer, showed a lower peak DOC concentration, a higher proportion of protein‐like DOM, and a higher contribution of cold season DOC flux to annual DOC flux when compared to the water flowing out from the permafrost area. Our work highlights the role of the thick, porous aquifer in the seasonally frozen area in regulating DOM export. The results suggest that the cold alpine area may exhibit a stronger positive feedback to climate warming than that in Arctic areas. Plain Language Summary: Permafrost degradation has resulted in the release of a large amount of soil carbon into streams, potentially affecting global carbon cycling. The mountainous areas on the Qinghai‐Tibet Plateau are characterized by the coexistence of permafrost and seasonally frozen areas and are sensitive to climate warming. To understand the export pattern of dissolved organic matter (DOM) through streams and its controlling factors on the Qinghai–Tibet Plateau, we analyzed the multi‐year chemical features of DOM in a representative catchment. We found that in the permafrost area, the soil freeze–thaw cycle and dilution of surface flow during warm season control the export of DOM. Compared to the water flowing out from the permafrost area, the stream water at the catchment outlet has a higher cold season dissolved organic carbon flux as percentage of the annual dissolved organic carbon flux, a lower peak concentration of dissolved organic carbon, and a higher proportion of protein‐like DOM. We attribute these differences to the effect of groundwater flow in the thick, porous aquifer in the seasonally frozen area, which has not been previously identified. We infer that this process may increase carbon loss rate when DOM is transported downstream on the Qinghai–Tibet Plateau. Key Points: Permafrost and seasonally frozen areas play different roles in driving riverine dissolved organic matter (DOM) export in an alpine catchmentGroundwater regulates seasonal variations in riverine DOM flux and compositionRiverine DOM characteristics differ in cold alpine and Arctic regions owing to contrasting hydrological processes [ABSTRACT FROM AUTHOR]

The Arctic is rapidly changing. Outside the Arctic, large-sample catchment databases have transformed catchment science from focusing on local case studies to more systematic studies of watershed functioning. Here we present an integrated pan-ARctic CAtchments summary DatabasE (ARCADE) of > 40 000 catchments that drain into the Arctic Ocean and range in size from 1 to 3.1 × 10 6 km 2. These watersheds, delineated at a 90 m resolution, are provided with 103 geospatial, environmental, climatic, and physiographic catchment properties. ARCADE is the first aggregated database of pan-Arctic river catchments that also includes numerous small watersheds at a high resolution. These small catchments are experiencing the greatest climatic warming while also storing large quantities of soil carbon in landscapes that are especially prone to degradation of permafrost (i.e., ice wedge polygon terrain) and associated hydrological regime shifts. ARCADE is a key step toward monitoring the pan-Arctic across scales and is publicly available: 10.34894/U9HSPV (Speetjens et al., 2022). [ABSTRACT FROM AUTHOR]

Arctic warming and sea level change will lead to widespread permafrost thaw and subsequent mobilization. Sedimentary records of past warming events during the Last Glacial–interglacial transition can be used to study the conditions under which permafrost mobilization occurs and which changes in vegetation on land are associated with such warming. The Amur and Yukon rivers discharging into the Okhotsk and Bering seas, respectively, drain catchments that have been, or remain until today, covered by permafrost. Here we study two marine sediment cores recovered off the mouths of these rivers. We use lignin phenols as biomarkers, which are excellently suited for the reconstruction of terrestrial higher plant vegetation, and compare them with previously published lipid biomarker data. We find that in the Yukon basin, vegetation change and wetland expansion began already in the early deglaciation (ED; 14.6–19 ka). This timing is different from observed changes in the Okhotsk Sea reflecting input from the Amur basin, where wetland expansion and vegetation change occurred later in the Pre-Boreal (PB). In the two basins, angiosperm contribution and wetland extent all reached maxima during the PB, both decreasing and stabilizing after the PB. The permafrost of the Amur basin began to become remobilized in the PB. Retreat of sea ice coupled with increased sea surface temperatures in the Bering Sea during the ED might have promoted early permafrost mobilization. In modern Arctic river systems, lignin and n -alkanes are transported from land to the ocean via different pathways, i.e., surface runoff vs. erosion of deeper deposits, respectively. However, accumulation rates of lignin phenols and lipids are similar in our records, suggesting that under conditions of rapid sea level rise and shelf flooding, both types of terrestrial biomarkers are delivered by the same transport pathway. This finding suggests that the fate of terrigenous organic matter in the Arctic differs on both temporal and spatial scales. [ABSTRACT FROM AUTHOR]

Ongoing climate change in the Arctic has caused tidewater glaciers to retreat while increasing the discharge of freshwater and terrestrial material into fjords. This can affect both nutrient inputs and cycling within the fjord systems. In particular, tidewater glaciers and the presence of associated subglacial meltwater plumes can have a large impact on fjord circulation and biogeochemistry. In this study, we assess the influence of tidewater glaciers on nitrogen inputs and cycling in two fjords in Svalbard during the summer using stable isotopic analyses of dissolved nitrate (δ15 N and δ18 O) in combination with nutrient and hydrographic data. Kongsfjorden receives inputs from tidewater glaciers, whereas Rijpfjorden mainly receives surface inputs from land-terminating glaciers. Results showed that both fjords are enriched in nutrients from terrestrial inputs. Nutrient ratios indicate excess Si and P relative to N. In both fjords, terrestrial nitrate from snowpack and glacier melting are identified as the dominant sources based on high δ18 O-NO 3- and low δ15 N-NO 3- of dissolved nitrate. In Kongsfjorden, mixed-layer nitrate is completely consumed within the fjord system, which we attribute to vigorous circulation at the glacial front influenced by the subglacial plume and longer residence time in the fjord. This is in contrast to Rijpfjorden where nutrients are only partially consumed perhaps due to surface river discharge and light limitation. In Kongsfjorden, we estimate terrestrial and marine N contributions to the nitrate pool from nitrogen isotopic values (δ15 N-NO 3-), and this suggests that nearly half the nitrate in the subglacial plume (50 ± 3 %) and the water column (44 ± 3 %) originates from terrestrial sources. We show that terrestrial N contributes significantly to the regenerated N pool (63 %–88 %) within this fjord suggesting its importance in sustaining productivity here. Given this importance of terrestrial nutrient sources within the fjords, increase in these inputs due to climate change can enhance the fjord nutrient inventory, productivity and nutrient export offshore. Specifically, increasing Atlantification and warmer Atlantic Water will encourage tidewater glacier retreat and in turn increase surface discharge. In fjords akin to Rijpfjorden this is expected to foster more light limitation and less dynamic circulation, ultimately aiding the export of nutrients offshore contributing to coastal productivity. Climate change scenarios postulated for fjords such as Kongsfjorden include more terrestrial N-fuelled productivity and N cycling within the fjord, less vigorous circulation due to the retreat of tidewater glaciers, and the expansion of oxygen-depleted deep waters isolated by the sill. [ABSTRACT FROM AUTHOR]

One of the most urgent problems on which current studies of Arctic and subarctic territories are focused is how permafrost thawing can affect organic carbon fluxes and how these fluxes can influence the geochemistry of the surface and ground water. In addition to disturbing the carbon balance, permafrost thawing provokes the release of a significant amount of other chemical elements entering natural waters. The paper presents original data obtained by studying surface water in 2020 in the Yamalo–Nenets Autonomous District, which is situated in the Arctic zone of the Russian Federation. Permafrost is widespread in the study area, as also are facilities of the oil and gas industry. This predetermines the importance of research on the chemical composition of natural water, its formation, and ecological–geochemical status, which are critical aspects for assessing the anthropogenic load and predicting the influence of climate changes on the biogeochemical cycles of chemical elements. In the course of our fieldwork, 47 surface water samples were taken in the basins of the Taz, Pur, Ob, and Nadym rivers: 23 samples from rivers and streams and 24 samples from lakes and thaw depressions. The sampling sites were chosen to as comprehensively as possible cover the lake–stream–river system in the catchment areas of major rivers of the Yamalo–Nenets Autonomous District. The chemical composition of the water samples was analyzed at a certified laboratory using methods conventionally applied in solving such problems. The data were processed using statistical methods, including the principal component analysis (PCA). Data analysis demonstrates that surface water in the study area is ultrafresh, with neutral or weakly alkaline pH values. Hydrocarbonate, calcium, and magnesium ions dominate in the ionic composition of the water, and ammonium contents are high in the waters of the lakes and thaw depressions. In addition, the ammonium concentration strongly positively correlates with the content of dissolved organic carbon (DOC) and the values of chemical oxygen demand (COD) and permanganate index (PI). It was found out that the streams (springs and rivers) differ from the lakes and the water of the thaw depressions in higher concentrations of main ions that are brought to the water mainly by natural factors (these are , Ca2+, Mg2+, and Na+) and higher total dissolved solids (TDS) and pH values. In contrast, the water of the thaw depressions is characterized by the highest concentrations of DOC and the values of other parameters related to organic matter (N– , COD, and PI). It was shown that the main factors that control the chemical composition of the water are its interaction with organic matter from organic (peat) soil horizons and the mineral components of the underlying rocks and soils. The former factor most significantly impacts the water of the thaw depressions, and the latter one affects mainly the chemical composition of the rivers and streams. The relatively high contents of the chloride and sodium ions in the water of the largest lakes are probably caused by the anthropogenic load. [ABSTRACT FROM AUTHOR]

In reconstructing past changes in precipitation or evaporation from the geologic record, paleoclimatologists sometimes employ the dual‐biomarker isotope method. This method requires that two co‐occurring sedimentary lipids are derived from different biological sources, and that their compound‐specific 2H/1H ratios record different aspects of the hydrologic cycle. Several studies have used this approach, typically by comparing the 2H/1H ratios of n‐alkyl lipids (δ2Hwax) thought to be sourced from aquatic versus terrestrial plants that gain their hydrogen atoms from lake water and soil water, respectively. Yet confidently fingerprinting n‐alkyl lipid sources continues to be a challenge because the wax inputs of different plant types vary across biomes, lake types, and time. New research in the Journal of Geophysical Research‐Biogeosciences by Hollister et al. (2022, https://doi.org/10.1029/2022jg006903) utilizes a combination of three independent metrics to demonstrate that for Arctic lakes, mid‐chain n‐alkanoic acids can be sourced principally from aquatic plants whereas long‐chain n‐alkanoic acids derive from a mixture of aquatic and terrestrial plants. By cataloging wax compound distributions and compound‐specific H and C isotopes of many new plant species, their efforts will strengthen future biomarker paleoclimatology and reinforce previous applications of the dual‐biomarker approach in high‐latitude lakes. The identification of a lake system with a strong aquatic plant wax signal in the sediments should motivate future targeting of similar lakes for reconstructing past moisture with the dual‐biomarker method. Plain Language Summary: Lake sediments accumulate leaf wax molecules made by plants that climate scientists can use to reconstruct past changes in precipitation and evaporation, key climate variables in the Earth system. For scientists to leverage information from these chemical fossils, they need to understand which plants are producing the waxes, and whether those plants gain their water from soils, from lakes, or from another water source. While land plants using soil water can dominate sedimentary wax signals, a recently published study indicates that exceptions occur in Arctic lakes with abundant aquatic plant growth. These advances support paleoclimate research and demonstrate an approach for fingerprinting the source of plant waxes in Arctic lakes. Key Points: Comparison of 2H/1H among differing sedimentary lipids can reveal paleohydrologic insights that single compounds cannotThe biological sources of mid‐chain n‐alkyl lipids to Arctic lake sediments remains debated because of variations between study sitesA new article by Hollister et al. (2022, https://doi.org/10.1029/2022jg006903) documents the contribution of aquatic plants to sedimentary waxes in Qaupat Lake, Baffin Island [ABSTRACT FROM AUTHOR]

This study traces dissolved organic matter (DOM) in different water masses of the Arctic Ocean and its effect on the distributions of trace elements (TEs; Fe, Cu, Mn, Ni, Zn, Cd) using fluorescent properties of DOM and the terrigenous biomarker lignin. The Nansen, Amundsen, and Makarov Basins were characterized by the influence of Atlantic water and the fluvial discharge of the Siberian Rivers with high concentrations of terrigenous DOM (tDOM). The Canada Basin and the Chukchi Sea were characterized by Pacific water, modified through contact with productive shelf sediments with elevated levels of marine DOM. Within the surface layer of the Beaufort Gyre, meteoric water (river water and precipitation) was characterized by low concentrations of lignin and tDOM fluorescence proxies as DOM is removed during freezing. High‐resolution in situ fluorescence profiles revealed that DOM distribution closely followed isopycnals, indicating the strong influence of sea‐ice formation and melt, which was also reflected in strong correlations between DOM fluorescence and brine contributions. The relationship of DOM and hydrography to TEs showed that terrigenous and marine DOM were likely carriers of dissolved Fe, Ni, Cu from the Eurasian shelves into the central Arctic Ocean. Chukchi shelf sediments were important sources of dCd, dZn, and dNi, as well as marine ligands that bind and carry these TEs offshore within the upper halocline in the Canada Basin. Our data suggest that tDOM components represent stronger ligands relative to marine DOM components, potentially facilitating the long‐range transport of TE to the North Atlantic. Plain Language Summary: The Arctic Ocean receives a disproportionate large amount of global river discharge and has limited but well‐constrained exchanges with other oceans. This makes the Arctic Ocean unique in terms of dissolved organic matter (DOM) and trace element (TE) sources and distribution. We used data collected during two expeditions spanning the entire Arctic Ocean to characterize the unique distribution of DOM and to study its potential as a water mass tracer and its role in the transport of TE. While the Atlantic‐dominated Nansen Basin was characterized by low levels of the DOM and TE, the central Arctic was dominated by the Transpolar Drift, a current that connects the Eurasian shelves to the Fram Strait and transports DOM from the Siberian Rivers toward the North Atlantic. In contrast, the Chukchi shelf‐Canada Basin region was characterized by the dominance of Pacific water that is enriched by marine DOM from the shallow and productive Chukchi shelf. The distribution of DOM from these different sources was affected by freezing and thawing processes and, therefore, can be used to study water mass transformations and pathways in the Arctic Ocean. Key Points: Dissolved Organic Matter (DOM) distribution in the Arctic Ocean is largely controlled by sea ice formation and melt processesDOM distribution in the Arctic Ocean reveals its potential as a tracer for halocline formation and freshwater source assignmentsTerrigenous and marine DOM are carriers of trace elements from shelves to the open Arctic Ocean, but terrigenous DOM represent stronger ligands [ABSTRACT FROM AUTHOR]

Large amounts of methane (CH4) could be released as a result of the gradual or abrupt thawing of Arctic permafrost due to global warming. Once available, this potent greenhouse gas is emitted into the atmosphere or transported laterally into aquatic ecosystems via hydrologic connectivity at the surface or via groundwaters. While high northern latitudes contribute up to 5 % of total global CH4 emissions, the specific contribution of Arctic rivers and streams is largely unknown. We analyzed high-resolution continuous CH4 concentrations measured between 15 and 17 June 2019 (late freshet) in a ∼120 km transect of the Kolyma River in northeast Siberia. The average partial pressure of CH4 (pCH4) in tributaries (66.8–206.8 µatm) was 2–7 times higher than in the main river channel (28.3 µatm). In the main channel, CH4 was up to 1600 % supersaturated with respect to atmospheric equilibrium. Key sites along the riverbank and at tributary confluences accounted for 10 % of the navigated transect and had the highest pCH4 (41 ± 7 µatm) and CH4 emissions (0.03 ± 0.004 mmolm-2d-1) compared to other sites in the main channel, contributing between 14 % to 17 % of the total CH4 flux in the transect. These key sites were characterized by warm waters (T>14.5 ∘C) and low specific conductivities (κ<88 µScm-1). The distribution of CH4 in the river could be linked statistically to T and κ of the water and to their proximity to the shore z , and these parameters served as predictors of CH4 concentrations in unsampled river areas. The abundance of CH4 -consuming bacteria and CH4 -producing archaea in the river was similar to those previously detected in nearby soils and was also strongly correlated to T and κ. These findings imply that the source of riverine CH4 is closely related with sites near land. The average total CH4 flux density in the river section was 0.02 ± 0.006 mmolm-2d-1 , equivalent to an annual CH4 flux of 1.24×107 gCH4yr-1 emitted during a 146 d open water season. Our study highlights the importance of high-resolution continuous CH4 measurements in Arctic rivers for identifying spatial and temporal variations, as well as providing a glimpse of the magnitude of riverine CH4 emissions in the Arctic and their potential relevance to regional CH4 budgets. [ABSTRACT FROM AUTHOR]

Herring gulls (Larus argentatus) are opportunistic feeders, resulting in contaminant exposure depending on area and habitat. We compared contaminant concentrations and dietary markers between two herring gull breeding colonies with different distances to extensive human activity and presumed contaminant exposure from the local marine diet. Furthermore, we investigated the integrity of DNA in white blood cells and sensitivity to oxidative stress. We analyzed blood from 15 herring gulls from each colony—the urban Oslofjord near the Norwegian capital Oslo in the temperate region and the remote Hornøya island in northern Norway, on the Barents Sea coast. Based on d13C and d34S, the dietary sources of urban gulls differed, with some individuals having a marine and others a more terrestrial dietary signal. All remote gulls had a marine dietary signal and higher relative trophic level than the urban marine feeding gulls. Concentrations (mean ± standard deviation [SD]) of most persistent organic pollutants, such as polychlorinated biphenyl ethers (PCBs) and perfluorooctane sulfonic acid (PFOS), were higher in urban marine (PCB153 17 ± 17 ng/g wet weight, PFOS 25 ± 21 ng/g wet wt) than urban terrestrial feeders (PCB153 3.7 ± 2.4 ng/g wet wt, PFOS 6.7 ± 10 ng/g wet wt). Despite feeding at a higher trophic level (d15N), the remote gulls (PCB153 17 ± 1221 ng/g wet wt, PFOS 19 ± 1421 ng/g wet wt) were similar to the urban marine feeders. Cyclic volatile methyl siloxanes were detected in only a few gulls, except for decamethylcyclopentasiloxane in the urban colony, which was found in 12 of 13 gulls. Only hexachlorobenzene was present in higher concentrations in the remote (2.6 ± 0.42 ng/g wet wt) compared with the urban colony (0.34 ± 0.33 ng/g wet wt). Baseline and induced DNA damage (doublestreak breaks) was higher in urban than in remote gulls for both terrestrial and marine feeders. Environ Toxicol Chem 2022;41:2466–2478. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The abundance, biomass, chlorophyll "a" concentration of picophytoplankton, contribution of picoalgae to total chlorophyll "a" and species composition of phototrophic picoeukaryotes (cells size less than 3 µm) were studied during 83 cruise of R/V Akademik Mstislav Keldysh in the Kara Sea in June 2021. The picophytoplankton abundance varied from 0.25 to 4.91 × 109 cell/m3, biomass–from 0.34 to 2.49 mg С/m3. The minimum abundance and biomass were found in the areas adjacent to the ice edge. The contribution of picophytoplankton to total chlorophyll a concentration in photic layer varied from 3 to 28% with maximum found in the stations free of ice more than 5 days. Picophytoplankton was represented by picoeukaryotes and cyanobacteria. The cyanobacteria contribution was low and varied from 0.2 to 1.8%. The Illumina sequencing of V4 region of 18S rRNA gene revealed that in the surface layer Chaetoceros socialis dominated in picoeukaryotes near ice edge during the diatom bloom. In the ice-free areas for more than 5 days small flagellates, such as Micromonas polaris, Phaeocystis pouchetii and Pyramimonas diskoicola, begin to develop in the surface layer after large phytoplankton descends to the lower horizon of upper mixed layer. [ABSTRACT FROM AUTHOR]

Intensifying permafrost thaw alters carbon cycling by mobilizing large amounts of terrestrial substrate into aquatic ecosystems. Yet, few studies have measured aquatic carbon fluxes and constrained drivers of ecosystem carbon balance across heterogeneous Arctic landscapes. Here, we characterized hydrochemical and landscape controls on fluvial carbon cycling, quantified fluvial carbon fluxes, and estimated fluvial contributions to ecosystem carbon balance across 33 watersheds in four ecoregions in the continuous permafrost zone of the western Canadian Arctic: unglaciated uplands, ice‐rich moraine, and organic‐rich lowlands and till plains. Major ions, stable isotopes, and carbon speciation and fluxes revealed patterns in carbon cycling across ecoregions defined by terrain relief and accumulation of organics. In previously unglaciated mountainous watersheds, bicarbonate dominated carbon export (70% of total) due to chemical weathering of bedrock. In lowland watersheds, where soil organic carbon stores were largest, lateral transport of dissolved organic carbon (50%) and efflux of biotic CO2 (25%) dominated. In watersheds affected by thaw‐induced mass wasting, erosion of ice‐rich tills enhanced chemical weathering and increased particulate carbon fluxes by two orders of magnitude. From an ecosystem carbon balance perspective, fluvial carbon export in watersheds not affected by thaw‐induced wasting was, on average, equivalent to 6%–16% of estimated net ecosystem exchange (NEE). In watersheds affected by thaw‐induced wasting, fluvial carbon export approached 60% of NEE. Because future intensification of thermokarst activity will amplify fluvial carbon export, determining the fate of carbon across diverse northern landscapes is a priority for constraining trajectories of permafrost region ecosystem carbon balance. Plain Language Summary: Freshwaters are a main component of the global carbon cycle and climate. Yet, their role in climate change is uncertain in permafrost regions, where thaw is releasing large amounts of carbon and enabling production of climate‐warming greenhouse gases. To reduce uncertainty, we measured stream chemistry and carbon fluxes across four ecoregions including a global hotspot of permafrost thaw in the western Canadian Arctic. Comparing across ecoregions, lowlands were strong sources of biological carbon dioxide and methane to the atmosphere; mountain rivers ferried products from chemical rock weathering downstream; and streams affected by permafrost thaw‐induced wasting transported large amounts of particulate carbon. Typical of northern ecosystems, carbon fluxes in non‐thaw‐affected streams were equivalent to 6%–16% of carbon uptake by terrestrial vegetation. However, in watersheds affected by thaw‐induced wasting, carbon fluxes were up to 100 times higher and approached 60% of vegetation carbon uptake. Together, these findings reveal that thermokarst‐susceptible terrains are poised to emerge as a significant component of the Arctic ecosystem carbon balance and global climate feedbacks, due to hydrologic carbon fluxes that will intensify as permafrost thaw accelerates. Key Points: Permafrost landscape history regulates fluvial carbon (C) sources and export across a transect of continental glaciation and thermokarstFluvial C flux equaled 6%–16% of vegetation C uptake in most watersheds and 60% in those affected by permafrost thaw‐driven mass wastingThaw‐susceptible terrains will be significant to Arctic ecosystem carbon balance as permafrost thaw and hydrologic carbon fluxes intensify [ABSTRACT FROM AUTHOR]

As arctic permafrost continues to thaw, previously inaccessible nitrogen (N) becomes available to N‐limited arctic plants. Increased N availability could enhance plant growth and thereby potentially offset climate‐induced carbon release. Arctic plants can take up newly available permafrost‐N locally upon release. However, in a topographically diverse arctic landscape, permafrost‐N may be transported along hillslopes, away from the point‐of‐release. The extent to which topographical N transport can impact arctic vegetation change depends on whether N is retained locally, captured by downslope recipient plant communities, or transported away.We used stable isotope labelling (15N) to simulate upslope release of ammonium (NH4+) and nitrate (NO3−) from thawing permafrost on an arctic hillslope, western Greenland. We tracked the plant species‐specific uptake of simulated permafrost‐released N from the upslope point‐of‐release to the bottom of the slope through 4 years.We found that arctic tundra plants successfully acquired locally released permafrost‐N, even in sloping terrain, and that N was strongly retained in the plant–soil system through multiple years. At the same time, we also importantly demonstrate that permafrost‐N can be transported and taken up by plants up to 30 m downslope from the point‐of‐release. Especially NO3− was more easily redistributed vertically within the soil column compared to NH4+ and therefore potentially more accessible to plants. Specifically, plant species with fast N uptake capacity and deep‐soil foraging strategies may have competitive advantages for capitalising on deep‐soil released and topographically transported permafrost‐N (here exemplified by Equisetum arvense and Salix glauca). Nevertheless, even mosses gained access to permafrost‐N via vertical and lateral redistribution on the slope. Ultimately, the intricate balance between strong local N retention, downslope transport and plant species‐specific uptake strategies may contribute to shaping arctic vegetation change.Synthesis. Across spatially complex arctic ecosystems, arctic plants can take up permafrost‐released N both at the local point‐of‐release and at a considerable distance downslope. The potential for arctic plants to take advantage of topographically transported permafrost‐N could lead to long‐term and landscape‐scale changes in species composition, plant productivity, and ultimately carbon and climate feedbacks across the Arctic. [ABSTRACT FROM AUTHOR]

We present ΔO2/Ar‐based estimates of mixed layer net community production (NCP) from three summer cruises in the North American Arctic and Subarctic oceans. Coupling shipboard underway and discrete observations with output from an ocean circulation model, we correct the NCP estimates for vertical mixing fluxes impacting the surface O2 budget. Large positive mixing fluxes, exceeding 100 mmol O2 m−2 d−1, were derived in regions of strong wind‐driven mixing, such as the Labrador Sea (LS), and in the physically‐dynamic Canadian Arctic Archipelago. In contrast, flux corrections were small (<10 mmol O2 m−2 d−1, on average) in the density‐stratified Baffin Bay, where mixing was low, and parts of the well‐mixed Hudson Strait (HS), where vertical O2 gradients were weak. The distribution of corrected NCP was highly heterogenous across the study region, reflecting varying contributions of nutrient supply, freshwater input and sea ice dynamics. Elevated NCP was apparent in the LS, HS, and nearshore regions influenced by glacial meltwater and recent ice retreat. Low NCP and localized net heterotrophy occurred in Baffin Bay, and near strong freshwater and organic matter sources in Hudson Bay and the Queen Maud Gulf. A multiple linear regression model developed using available oceanographic data explained ∼58% of the observed NCP variability. Our work demonstrates the spatially explicit influence of vertical mixing on ΔO2/Ar‐based NCP calculations across varied hydrographic conditions, and presents a novel approach to account for this process. This study contributes new knowledge of biological productivity distributions in under‐sampled, rapidly changing, high‐latitude waters. Plain Language Summary: Net community production (NCP; i.e., net organic matter production) constrains the ocean's ability to support marine ecosystems and remove carbon dioxide from the atmosphere. A common approach to estimating NCP involves measurements of upper ocean oxygen (O2) concentrations. However, while vertical mixing may be a significant component of the surface water O2 budget in some regions, applications of this approach typically do not quantify the magnitude of this flux, which can lead to potentially inaccurate NCP estimates. In this paper, we introduce a method combining ship‐based measurements and the output from an ocean circulation model to refine NCP calculations for vertical mixing effects in North American Arctic and Subarctic oceans. The data set reveals high NCP in the Labrador Sea (Inuktitut: Lâbradorip Imappinga), North Atlantic, Hudson Strait (Ikirasarjuaq) and northern Canadian Arctic Archipelago (CAA), and low values in Baffin Bay (Saknirutiak Imanga) and southern CAA. Riverine freshwater input to Hudson Bay (Tasiujarjuar) and the Queen Maud Gulf (Ugjulik) can reduce local NCP, while glacial meltwater may stimulate NCP elsewhere. Overall, this work provides a new NCP data set in an under‐sampled region. Similar studies will be necessary to document changes in biological productivity in response to changing environmental conditions in polar waters. Key Points: Ship‐based observations and numerical model output were used to correct net community production (NCP) estimates for vertical mixing biasesCorrected NCP was correlated with nutrient supply and sea ice dynamics, as reflected in a multiple linear regressionFreshwater from glaciers and rivers may stimulate productivity or drive local respiration through nutrient and organic carbon inputs [ABSTRACT FROM AUTHOR]

The rapid evolution of science compels renewal of a knowledge-based policy, particularly in cold regions. In the Arctic and Himalayas, which have undergone a significant climate change, there is a disconnect between scientific knowledge and the practices of policy. The rising air temperatures, decreasing ice and snow, increasing precipitation and plastic waste pollutants and the Atlantification of the Arctic Ocean by receiving warmer and saltier water from the Atlantic Ocean call for scientific research questions to strengthen the linkage between science and policy. The Arctic amplification can have remote impacts on other parts of the globe through oceanic and atmospheric teleconnections. Hence, researchers need to push the frontiers of scientific discoveries through multidisciplinary and collaborative approaches in the Arctic Ocean along with connections to the Third Pole – Himalayas. The overall objectives of this paper are to explore how a comparison of the Arctic and the Third Pole is valuable for understanding the Arctic and global biogeophysical processes in this epoch of anthropogenic climate change; provide a strong linkage between the Arctic scientific research and its relevance to society; and help advance a more sustainable future for the Arctic, the Third Pole and the globe. [ABSTRACT FROM AUTHOR]

Fires are predicted to increase in Arctic regions due to ongoing climate change. Tundra fires can alter carbon and nutrient cycling and release a substantial quantity of greenhouse gases with global consequences. Yet, the long-term effects of tundra fires on carbon (C) and nitrogen (N) stocks and cycling are still unclear. Here we used a space-for-time approach to investigate the long-term fire effects on C and N stocks and cycling in soil and aboveground living biomass. We collected data from three large fire scars (>44 , 28, and 12 years old) and corresponding control areas and used linear mixed-effect models in a Bayesian framework to analyse long-term development of C and N stocks and cycling after fire. We found that tundra fires had no long-term effect on total C and N stocks because a major part of the stocks was located belowground in soils which were largely unaltered by fire. However, fire had a strong long-term effect on stocks in the aboveground vegetation, mainly due to the reduction in the lichen layer. Fire reduced N concentrations in graminoids and herbs on the younger fire scars, which affected respective C/N ratios and may indicate an increased post-fire competition between vascular plants. Aboveground plant biomass was depleted in 13C in all three fire scars. In soil, the relative abundance of 13C changed with time after fire. Our results indicate that in lichen-rich subarctic tundra ecosystems, the contribution of fires to the release of additional carbon to the atmosphere might be relatively small as soil stocks appear to be resilient within the observed time frame. [ABSTRACT FROM AUTHOR]

In Arctic ecosystems, increasing temperatures are driving the expansion of nitrogen (N) fixing shrubs across tundra landscapes. The implications of this expansion to the biogeochemistry of Arctic ecosystems are of critical importance and more work is needed to better understand the form, availability, and transportation potential of N from these shrubs across a variety of Arctic landscapes. To gain insights into the processes controlling N within a permafrost hillslope system, the spatiotemporal variability of nitrate (NO 3-) and its environmental controls were investigated at an alder (Alnus viridis spp. fruticosa) dominated permafrost tundra landscape in the Seward Peninsula, Alaska, USA. Soil pore water was collected from locations within alder shrubland growing along a well-drained hillslope and was compared to soil pore water collected from locations outside (upslope, downslope, and between) the alder shrubland. Soil pore water collected within alder shrubland had an average NO 3 -N (nitrogen from nitrate) concentration of 4.27±8.02 mg L -1 and differed significantly from locations outside alder shrubland (0.23±0.83 mg L -1 ; p<0.05). Temporal variation in NO 3 -N within and downslope of alder shrubland co-occurred with precipitation events where NO 3- that accumulated in the soil was likely flushed downslope during rainfall. These findings have important implications for nutrient availability and mobility in N-limited permafrost systems that are experiencing shrub expansion in response to a warming Arctic. [ABSTRACT FROM AUTHOR]

Peatland biogeochemical processes have not been adequately represented in existing earth system models, which might have biased the quantification of Arctic carbon‐climate feedbacks. We revise the Peatland Terrestrial Ecosystem Model (PTEM) by incorporating additional peatland biogeochemical processes. The revised PTEM is evaluated by comparing with Holocene Peatland Model (HPM) in simulating peat physical and biogeochemical dynamics in three North American peatlands: a permafrost‐free fen site, a permafrost‐free bog site and a permafrost bog site. Peatland carbon dynamics are simulated from peat initiation to 1990 and then to year 2300. Model responses to the changes in temperature and precipitation are analyzed to identify key processes affecting peatland carbon accumulation rates. We find that the net C balance is sensitive to water table depth and nutrient availability. Future simulations to year 2300 are conducted with both models under RCP 2.6, RCP 4.5, and RCP 8.5. PTEM predicts these peatlands to be C sources or weaker C sinks when insufficient precipitation suppresses soil moisture and thereby net N mineralization and net primary production, while HPM predicts the same when drier climate leads to increasing water table depth. Our results highlight the importance of water balance and C‐N feedback on peatland C dynamics. With a warmer climate, these peatlands could become a weaker C sink or a source under drier conditions, otherwise a larger C sink if wetter. Improved understanding to peatland processes can help future quantification of peatland C dynamics in the boreal and Arctic regions. Plain Language Summary: We revise a process‐based Peatland Terrestrial Ecosystem Model (PTEM) by incorporating additional peatland biogeochemical processes. The model is compared with the Holocene Peatland Model (HPM) by simulating peatland dynamics at three peatland sits: a permafrost‐free fen site, a permafrost‐free bog site and a permafrost bog site. The simulation starts from peat initiation to 1990, and then to 2300. We find that peatland productivity is sensitive to water table depth and nutrient availability. PTEM predicts these peatlands to be C sources or weaker C sinks when insufficient precipitation suppresses soil moisture and thereby nutrient availability and vegetation productivity. HPM predicts the same trend when drier climate leads to increasing water table depth. Our results highlight the importance of water balance and C‐N feedback in peatland C dynamics in peatland C modeling. Key Points: Peatlands tend to be C sources or weaker C sinks when insufficient precipitation suppresses net N mineralization and net primary productionPeatlands tend to be C sources or weaker C sinks when drier climate leads to increasing water table depthBoth C‐N feedback and water table change are important factors influencing peatland C balance [ABSTRACT FROM AUTHOR]

The Arctic Ocean is considered a source of micronutrients to the Nordic Seas and the North Atlantic Ocean through the gateway of Fram Strait (FS). However, there is a paucity of trace element data from across the Arctic Ocean gateways, and so it remains unclear how Arctic and North Atlantic exchange shapes micronutrient availability in the two ocean basins. In 2015 and 2016, GEOTRACES cruises sampled the Barents Sea Opening (GN04, 2015) and FS (GN05, 2016) for dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn). Together with the most recent synopsis of Arctic‐Atlantic volume fluxes, the observed trace element distributions suggest that FS is the most important gateway for Arctic‐Atlantic dissolved micronutrient exchange as a consequence of Intermediate and Deep Water transport. Combining fluxes from FS and the Barents Sea Opening with estimates for Davis Strait (GN02, 2015) suggests an annual net southward flux of 2.7 ± 2.4 Gg·a−1 dFe, 0.3 ± 0.3 Gg·a−1 dCo, 15.0 ± 12.5 Gg·a−1 dNi and 14.2 ± 6.9 Gg·a−1 dCu from the Arctic toward the North Atlantic Ocean. Arctic‐Atlantic exchange of dMn and dZn were more balanced, with a net southbound flux of 2.8 ± 4.7 Gg·a−1 dMn and a net northbound flux of 3.0 ± 7.3 Gg·a−1 dZn. Our results suggest that ongoing changes to shelf inputs and sea ice dynamics in the Arctic, especially in Siberian shelf regions, affect micronutrient availability in FS and the high latitude North Atlantic Ocean. Plain Language Summary: Recent studies have proposed that the Arctic Ocean is a source of micronutrients such as dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn) to the North Atlantic Ocean. However, data at the Arctic Ocean gateways including Fram Strait and the Barents Sea Opening have been missing to date and so the extent of Arctic micronutrient transport toward the Atlantic Ocean remains unquantified. Here, we show that Fram Strait is the most important gateway for Arctic‐Atlantic micronutrient exchange which is a result of deep water transport at depths >500 m. Combined with a flux estimate for Davis Strait, this study suggests that the Arctic Ocean is a net source of dFe, dNi and dCu, and possibly also dCo, toward the North Atlantic Ocean. Arctic‐Atlantic dMn and dZn exchange seems more balanced. Properties in the East Greenland Current showed substantial similarities to observations in the upstream Central Arctic Ocean, indicating that Fram Strait may export micronutrients from Siberian riverine discharge and shelf sediments >3,000 km away. Increasing Arctic river discharge, permafrost thaw and coastal erosion, all consequences of ongoing climate change, may therefore alter future Arctic Ocean micronutrient transport to the North Atlantic Ocean. Key Points: Fram Strait is the major gateway for Arctic‐Atlantic exchange of the dissolved micronutrients Fe, Mn, Co, Ni, Cu and ZnThe Arctic is a net source of dissolved Fe, Co, Ni and Cu to the Nordic Seas and toward the North Atlantic; Mn and Zn exchange are balancedWaters of the Central Arctic Ocean, including the Transpolar Drift, are the main drivers of gross Arctic micronutrient export [ABSTRACT FROM AUTHOR]

Arctic lakes store, modify, and transport large quantities of carbon from terrestrial environments to the atmosphere; however, the spatial and temporal relationships between quantity and composition of dissolved organic matter (DOM) have not been well characterized across broad arctic regions. Moreover, most arctic lake DOM compositions have been examined during the ice‐free summer, whereas DOM cycling between the ice‐covered winter months and summer have not been addressed. To resolve these spatial and seasonal uncertainties in DOM cycling, we sampled a series of arctic lakes from the North Slope of Alaska across a latitudinal gradient in the winter and summer over 3 years. Samples were analyzed for dissolved organic carbon concentration and DOM composition was characterized using optical and fluorescence properties combined with molecular‐level analysis using Fourier transform‐ion cyclotron resonance mass spectrometry. Tundra lake DOM properties including aromaticity and molecular stoichiometries were similar to other northern high‐latitude lakes, but optical parameters related to aromaticity and molecular weight were greater in major arctic rivers and in coastal lakes in the North Slope region. DOM composition was highly seasonal, with ice exclusion concentrating microbially processed DOM in the winter water columns, potentially influencing DOM cycling the following summer. However, the greatest variations in DOM composition were related to lake depth and likely other physical features including morphology and bathymetry. As the Arctic warms, we expect changes in hydrology and ice cover to enhance under‐ice microbial DOM processing, early summer photodegradation, and ultimately carbon fluxes to the atmosphere after ice‐out. Plain Language Summary: Arctic lakes contain large amounts of both inorganic and dissolved organic carbon (DOC) that is stored, processed, and transferred to the atmosphere. This cycling has been enhanced by recent arctic warming via anthropogenic climate change, making the fate and distribution of these different pools uncertain on both seasonal and spatial scales. We demonstrate that the amount of DOC and the composition of dissolved organic matter (DOM) vary significantly across tundra lakes between summer and winter months when the lakes are entirely covered by ice. Furthermore, these seasonal trends are consistent across the North Slope of Alaska with lakes closer to the coast of the Arctic Ocean differing in bulk optical and molecular‐level properties, suggesting DOM is supplied by different sources and influenced by maritime effects. Finally, while seasonality was an important factor in explaining DOM compositions across the tundra, the greatest differences between lakes were attributed to other factors, likely related to the variations in lake geomorphology including lake depth and area across the region. As temperatures and precipitation change across the Arctic are expected, lake morphology will respond to a thawing landscape and influence the composition of DOM as well as how it is cycled from lakes to the atmosphere. Key Points: Dissolved organic carbon concentration and dissolved organic matter (DOM) composition differ seasonally due to ice exclusion and microbial processing in the winter monthsLake geomorphology is likely a major control for the overall lake DOM composition across the arctic tundraTundra lake DOM composition differs in optical properties and heteroatomic content between coastal and inland lakes [ABSTRACT FROM AUTHOR]

Information about the dietary composition of a species is crucial to understanding their position and role in the food web. Increasingly, molecular approaches such as DNA metabarcoding are used in studying trophic relationships, not least because they may alleviate problems such as low taxonomic resolution or underestimation of digestible taxa in the diet. Here, we used DNA metabarcoding with universal primers for cytochrome c oxidase I (COI) to study the diet composition of the northern shrimp (Pandalus borealis), an Arctic keystone species with large socio‐economic importance. Across locations, jellyfish and chaetognaths were the most important components in the diet of P. borealis, jointly accounting for 40%–60% of the total read abundance. This dietary importance of gelatinous zooplankton contrasts sharply with published results based on stomach content analysis. At the same time, diet composition differed between fjord and shelf locations, pointing to different food webs supporting P. borealis in these two systems. Our study underlines the potential of molecular approaches to provide new insights into the diet of marine invertebrates that are difficult to obtain with traditional methods, and calls for a revision of the role of gelatinous zooplankton in the diet of the key Arctic species P. borealis, and in extension, Arctic food webs. [ABSTRACT FROM AUTHOR]

Freshwater chemistry across the circumpolar region was characterised using a pan‐Arctic data set from 1,032 lake and 482 river stations. Temporal trends were estimated for Early (1970–1985), Middle (1986–2000), and Late (2001–2015) periods. Spatial patterns were assessed using data collected since 2001.Alkalinity, pH, conductivity, sulfate, chloride, sodium, calcium, and magnesium (major ions) were generally higher in the northern‐most Arctic regions than in the Near Arctic (southern‐most) region. In particular, spatial patterns in pH, alkalinity, calcium, and magnesium appeared to reflect underlying geology, with more alkaline waters in the High Arctic and Sub Arctic, where sedimentary bedrock dominated.Carbon and nutrients displayed latitudinal trends, with lower levels of dissolved organic carbon (DOC), total nitrogen, and (to a lesser extent) total phosphorus (TP) in the High and Low Arctic than at lower latitudes. Significantly higher nutrient levels were observed in systems impacted by permafrost thaw slumps.Bulk temporal trends indicated that TP was higher during the Late period in the High Arctic, whereas it was lower in the Near Arctic. In contrast, DOC and total nitrogen were both lower during the Late period in the High Arctic sites. Major ion concentrations were higher in the Near, Sub, and Low Arctic during the Late period, but the opposite bulk trend was found in the High Arctic.Significant pan‐Arctic temporal trends were detected for all variables, with the most prevalent being negative TP trends in the Near and Sub Arctic, and positive trends in the High and Low Arctic (mean trends ranged from +0.57%/year in the High/Low Arctic to −2.2%/year in the Near Arctic), indicating widespread nutrient enrichment at higher latitudes and oligotrophication at lower latitudes.The divergent P trends across regions may be explained by changes in deposition and climate, causing decreased catchment transport of P in the south (e.g. increased soil binding and trapping in terrestrial vegetation) and increased P availability in the north (deepening of the active layer of the permafrost and soil/sediment sloughing). Other changes in concentrations of major ions and DOC were consistent with projected effects of ongoing climate change. Given the ongoing warming across the Arctic, these region‐specific changes are likely to have even greater effects on Arctic water quality, biota, ecosystem function and services, and human well‐being in the future. [ABSTRACT FROM AUTHOR]

Mosses are ubiquitous in northern terrestrial ecosystems, and play an important role in regional carbon, water and energy cycling. Current global land surface models that do not consider mosses may bias the quantification of regional carbon dynamics. Here we incorporate mosses as a new plant functional type into the process-based Terrestrial Ecosystem Model (TEM 5.0), to develop a new model (TEM_Moss). The new model explicitly quantifies the interactions between vascular plants and mosses and their competition for energy, water, and nutrients. Compared to the estimates using TEM 5.0, the new model estimates that the regional terrestrial soils currently store 132.7 Pg more C and will store 157.5 and 179.1 Pg more C under the RCP8.5 and RCP2.6 scenarios, respectively, by the end of the 21st century. Ensemble regional simulations forced with different parameters for the 21st century with TEM_Moss predict that the region will accumulate 161.1±142.1 Pg C under the RCP2.6 scenario and 186.7±166.1 Pg C under the RCP8.5 scenario over the century. Our study highlights the necessity of coupling moss into Earth system models to adequately quantify terrestrial carbon–climate feedbacks in the Arctic. [ABSTRACT FROM AUTHOR]

Climate change is causing drastic landscape changes in the Arctic, but how these changes modify stream biogeochemistry is not clear yet. We examined how catchment properties influence stream nitrogen (N) and dissolved organic carbon concentrations (DOC) in a high‐Arctic environment. We sampled two contrasting headwater streams (10–15 stations over 4.8 and 6.8 km, respectively) in Northeast Greenland (74°N). We characterized the geomorphology (i.e., bedrock, solifluction and alluvial types) and the vegetation (i.e., barren, fell field, grassland and tundra types) cover of each subcatchment area draining into each sampling station and collected water samples for hydrochemistry characterization. The two sampled streams differed in geomorphology and vegetation cover in the catchment. Aucellaelv catchment was mostly covered by a 'bedrock' geomorphology (71%) and 'fellfield' vegetation (51%), whereas Kæerelv was mostly covered by 'alluvial' geomorphology (65%) and 'grassland' and 'tundra' vegetation (42% and 41% respectively). Hydrochemistry also differed between the two study streams, with higher concentrations of inorganic N forms in Aucellaelv and lower DOC concentrations, compared to Kærelv. The results from the linear mixed model selection showed that vegetation and geomorphology had contrasting effects on stream hydrochemistry. Subcatchments with higher solifluction sheets and limited vegetation had higher nitrate concentrations but lower DOC concentrations. Interestingly, we also found high variability on the production and removal of nitrate across subcatchments. These results indicate landscape controls to nutrient and organic matter exports via flow paths, soil organic matter stocks and nutrient retention via terrestrial vegetation. Moreover, the results suggest that climate change induced alterations to vegetation cover and soil physical disturbance in high‐Arctic catchments will affect stream hydrochemistry, with potential effects in stream productivity, trophic relations as well as change of solute export to downstream coastal areas. [ABSTRACT FROM AUTHOR]

The mobilization and land‐to‐ocean transfer of dissolved organic carbon (DOC) in Arctic watersheds is intricately linked with the region's climate and water cycle, and furthermore at risk of changes from climate warming and associated impacts. This study quantifies model‐simulated estimates of runoff, surface and active layer leachate DOC concentrations and loadings to western Arctic rivers, specifically for basins that drain into coastal waters between and including the Yukon and Mackenzie Rivers. Model validation leverages data from other field measurements, synthesis studies, and modeling efforts. The simulations effectively quantify DOC leaching in surface and subsurface runoff and broadly capture the seasonal cycle in DOC concentration and mass loadings reported from other studies that use river‐based measurements. A marked east‐west gradient in simulated spring and summer DOC concentrations of 24 drainage basins on the North Slope of Alaska is captured by the modeling, consistent with independent data derived from river sampling. Simulated loadings for the Mackenzie and Yukon show reasonable agreement with estimates of DOC export for annual totals and four of the six seasonal comparisons. Nearly equivalent loading occurs to rivers which drain north to the Beaufort Sea and west to the Bering and Chukchi Seas. The modeling framework provides a basis for understanding carbon export to coastal waters and for assessing impacts of hydrological cycle intensification and permafrost thaw with ongoing warming in the Arctic. Plain Language Summary: Arctic rivers transfer a relatively large amount of freshwater to the Arctic Ocean compared to other oceans. The rivers contain organic carbon dissolved in the water, with the bulk arriving during the high flow in spring that follows snowmelt. There is evidence that climate warming is thawing permafrost and resulting in more carbon traveling through rivers to the Arctic Ocean, so it is important to understand how much enters river networks from soils. We used a computer model designed to capture the seasonal thawing and freezing of Arctic soils and seasonal snowpack accumulation to estimate how much dissolved organic carbon is loaded to rivers in the western Arctic over the period 1981 to 2010. For northern Alaska rivers the simulation shows a gradient in dissolved organic carbon concentration from the east side to the west, similar to the pattern in independent data derived from river measurements. Our new estimates suggest that roughly equivalent amounts of dissolved organic carbon are loaded to rivers which empty north to the Beaufort Sea, and west to the Bering and Chukchi Seas. The modeling allows us to better understand how climate change is impacting flows of water and carbon to the Arctic Ocean. Key Points: Modeling quantifies daily DOC loadings in surface and subsurface runoff into river networks across the western ArcticSimulation captures a gradient in seasonal DOC concentrations for North Slope Alaska rivers consistent with field measurementsSimilar loadings are estimated for basins draining to the north and to the west [ABSTRACT FROM AUTHOR]

Climate change in the Arctic is altering the delivery of nutrients from terrestrial to aquatic ecosystems. The impact of these changes on downstream lakes and rivers is influenced by the capacity of small streams to retain such inputs. Given the potential for nutrient limitation in oligotrophic Arctic streams, biotic demand should be high, unless harsh environmental conditions maintain low biomass standing stocks that limit nutrient uptake capacity.We assessed the drivers of nutrient uptake in two contrasting headwater environments in Arctic Sweden: one stream draining upland tundra and the other draining an alluvial valley with birch forest. At both sites, we measured nitrate (NO3−) uptake biweekly using short‐term slug releases and estimated rates of gross primary production (GPP) and ecosystem respiration from continuous dissolved oxygen measurements.Catchment characteristics were associated with distinct stream chemical and biological properties. For example, the tundra stream maintained relatively low NO3− concentrations (average: 46 µg N/L) and rates of GPP (0.2 g O2 m−2 day−1). By comparison, the birch forest stream was more NO3− rich (88 µg N/L) and productive (GPP: 1.7 g O2 m−2 day−1). These differences corresponded to greater areal NO3− uptake rate and increased NO3− use efficiency (as uptake velocity) in the birch forest stream (max 192 µg N m−2 min−1 and 96 mm/hr) compared to its tundra counterpart (max 52 µg N m−2 min−1 and 49 mm/hr) during 2017. Further, different sets of environmental drivers predicted temporal patterns of nutrient uptake at these sites: abiotic factors (e.g. NO3− concentration and discharge) were associated with changes in uptake in the tundra stream, while metabolic activity was more important in the birch forest stream.Between sites, variation in uptake metrics suggests that the ability to retain pulses of nutrients is linked to nutrient supply regimes controlled at larger spatial and temporal scales and habitat properties that promote biomass accrual and thus biotic demand.Overall, constraints on biotic potential imposed by the habitat template determined the capacity of these high latitude streams to respond to future changes in nutrient inputs arising from climate warming or human land use. ​ [ABSTRACT FROM AUTHOR]

Thermokarst lakes are potentially important sources of methane (CH 4 ) and carbon dioxide (CO 2 ). However, considerable uncertainty exists regarding carbon emissions from thermokarst lakes owing to a limited understanding of their patterns and motivators. In this study, we measured CH 4 and CO 2 diffusive fluxes in 163 thermokarst lakes in the Qinghai-Tibet Plateau (QTP) over 3 years from May to October. The median carbon emissions from the QTP thermokarst lakes were 1440 mg CO 2 m -2 day -1 and 60 mg CH 4 m -2 day -1 , respectively. The diffusive rates of CO 2 and CH 4 are related to the catchment land cover type. Sediment microbial abundance and hydrochemistry explain 51.9% and 38.3% of the total variance in CH 4 diffusive emissions, respectively, while CO 2 emissions show no significant relationship with environmental factors. When upscaling carbon emissions from the QTP thermokarst lakes, the annual average CH 4 release per lake area is equal to that of the pan-Arctic region. Our findings highlight the importance of incorporating in situ observation data with different emission pathways for different land cover types in predicting carbon emissions from thermokarst lakes in the future., (© 2023 John Wiley & Sons Ltd.)

Increasing Arctic temperatures are thawing permafrost soils and liberating ancient organic matter, but the fate of this material remains unclear. Thawing of permafrost releases dissolved organic matter (DOM) into fluvial networks. Unfortunately, tracking this material in Arctic rivers such as the Kolyma River in Siberia has proven challenging due to its high biodegradability. Here, we evaluate late summer abruptly thawed yedoma permafrost dissolved organic carbon (DOC) inputs from Duvannyi Yar. We implemented ultrahigh‐resolution mass spectrometry alongside ramped pyrolysis oxidation (RPO) and isotopic analyses. These approaches offer insight into DOM chemical composition and DOC radiocarbon values of thermochemical components for a permafrost thaw stream, the Kolyma River, and their biodegraded counterparts (n = 4). The highly aliphatic molecular formula found in undegraded permafrost DOM contrasted with the comparatively aliphatic‐poor formula of Kolyma River DOM, represented by an 8.9% and 2.6% relative abundance, respectively, suggesting minimal inputs of undegraded permafrost DOM in the river. RPO radiocarbon fractions of Kolyma River DOC exhibited no "hidden" aged component indicative of permafrost influence. Thermostability analyses suggested that there was limited biodegraded permafrost DOC in the Kolyma River, in part determined by the formation of high‐activation energy (thermally stable) biodegradation components in permafrost DOM that were lacking in the Kolyma River. A mixing model based on thermostability and radiocarbon allowed us to estimate a maximum input of between 0.8% and 7.7% of this Pleistocene‐aged permafrost to the Kolyma River DOC. Ultimately, our findings highlight that export of modern terrestrial DOC currently overwhelms any permafrost DOC inputs in the Kolyma River. Plain Language Summary: Climate change is warming the Arctic faster than anywhere on Earth. Permafrost, or frozen soil, contains a vast amount of carbon locked in an icy repository. With warming temperatures, permafrost is thawing, and this thawed organic material can be transformed by microbes into greenhouse gases, leading to further warming. The amount of permafrost thawing into rivers, however, has been difficult to determine. In this study, we examined material in both permafrost thaw water, and thaw water material degraded by microbes, then compared it to material in a major Arctic river to see if we can find a sign of permafrost inputs. Permafrost is also very old and this old carbon mixes with modern sources of carbon in the river. We used a new analytical technique to see if we could find old carbon derived from permafrost in the river during late summer when permafrost thaw inputs are greatest. Even with the novel approach, we found little evidence of old carbon, suggesting that major Arctic rivers are currently only exporting a limited amount of permafrost carbon to the Arctic Ocean. This research highlights that the exported carbon is predominantly from plants and other contemporary sources within the watershed. Key Points: Molecular composition indicated minimal inputs of microbially unaltered permafrost thaw dissolved organic carbon (DOC) into the Kolyma RiverThermochemical composition and radiocarbon ages indicated minimal inputs of 28‐days microbially degraded permafrost thaw DOCNo directly permafrost‐aged component was evident in underlying age structure of Kolyma River DOC [ABSTRACT FROM AUTHOR]

The Arctic–boreal zone (ABZ) is experiencing amplified warming, actively changing biogeochemical cycling of vegetation and soils. The land-to-atmosphere fluxes of CO2 in the ABZ have the potential to increase in magnitude and feedback to the climate causing additional large-scale warming. The ability to model and predict this vulnerability is critical to preparation for a warming world, but Earth system models have biases that may hinder understanding of the rapidly changing ABZ carbon fluxes. Here we investigate circumpolar carbon cycling represented by the Community Land Model 5 (CLM5.0) with a focus on seasonal gross primary productivity (GPP) in plant functional types (PFTs). We benchmark model results using data from satellite remote sensing products and eddy covariance towers. We find consistent biases in CLM5.0 relative to observational constraints: (1) the onset of deciduous plant productivity to be late; (2) the offset of productivity to lag and remain abnormally high for all PFTs in fall; (3) a high bias of grass, shrub, and needleleaf evergreen tree productivity; and (4) an underestimation of productivity of deciduous trees. Based on these biases, we focus on model development of alternate phenology, photosynthesis schemes, and carbon allocation parameters at eddy covariance tower sites. Although our improvements are focused on productivity, our final model recommendation results in other component CO2 fluxes, e.g., net ecosystem exchange (NEE) and terrestrial ecosystem respiration (TER), that are more consistent with observations. Results suggest that algorithms developed for lower latitudes and more temperate environments can be inaccurate when extrapolated to the ABZ, and that many land surface models may not accurately represent carbon cycling and its recent rapid changes in high-latitude ecosystems, especially when analyzed by individual PFTs. [ABSTRACT FROM AUTHOR]

The Kuparuk River, located on Alaska's North Slope, is one of the most studied rivers in the Arctic. For nearly 40 seasons, physical, chemical, and biological parameters have been monitored continuously in a 5 km, 4th‐order reach of the river during the short summer season when there is flow in this river. Flow decreases as the tundra begins to refreeze in the late autumn and these streams normally remain frozen until the spring freshet. The monitoring program has supported a 34‐year phosphorus enrichment experiment conducted by the Arctic Long Term Ecological Research (LTER) program. Enrichment with phosphorus dramatically changed the structure and function of the primary producer community in the fertilized reach, with cascading effects in higher trophic levels. The datasets generated by this experiment have revealed significant increases in flow‐weighted mean concentrations of nitrate and significant decreases in flow‐weighted mean concentrations of dissolved organic N and P over time. In this paper, we present an overview of the nutrient concentration, discharge, macroinvertebrate, and Arctic grayling population datasets we have collected. The purposes of these datasets are to track changes resulting from the enrichment experiment, support ancillary research on responses of an Arctic stream to climate warming and permafrost thaw, and to provide input and validation data for models to predict future changes in Arctic streams. [ABSTRACT FROM AUTHOR]

Over the past 30 plus years, the Arctic has warmed at a rate of 0.6°C per decade. This has resulted in considerable permafrost thaw and alterations of hydrological and biogeochemical processes. Coincident with these changes, recent studies document increases in annual fluxes of inorganic nutrients in larger Arctic rivers. Changing nutrient fluxes in Arctic rivers have been largely attributed to warming‐induced active layer expansion and newly exposed subsurface source areas. However, the ability of Arctic headwater streams to modulate inorganic nutrient patterns manifested in larger rivers remains unresolved. We evaluated environmental conditions, stream ecosystem metabolism, and nutrient uptake in three headwater streams of the Alaskan Arctic to quantify patterns of retention of inorganic nitrogen (N) and phosphorous (P). We observed elevated ambient nitrate‐N (NO3‐N) concentrations in late summer/early fall in two of three experimental stream reaches. We observed detectable increases in uptake as a result of nutrient addition in 88% of PO4‐P additions (n = 25), 38% of NH4‐N additions (n = 24), and 24% of NO3‐N additions (n = 25). We observed statistically significant relationships between NH4‐N uptake and ecosystem respiration, and PO4‐P uptake and gross primary productivity. Although these headwater streams demonstrate ability to control downstream transport of PO4‐P, we observed little evidence the same holds for dissolved inorganic N. Consequently, our results suggest that continued increases in terrestrial to aquatic N transfer in Arctic headwater landscapes are likely to be evident in larger Arctic rivers, in‐network lakes, and coastal environments. Key Points: Upstream presence/absence of lakes is an important determinant of patterns in nutrient concentrations in three Arctic headwater streamsIn‐stream biological demand is high for added phosphate but low for additional inorganic nitrogenConsequently, continued and/or increased inorganic nitrogen loading to headwater streams is likely to be transferred to coastal environments in Arctic ecosystems [ABSTRACT FROM AUTHOR]

Arctic regions and their water bodies are affected by a rapidly warming climate. Arctic lakes and small ponds are known to act as an important source of atmospheric methane. However, not much is known about other types of water bodies in permafrost regions, which include major rivers and coastal bays as a transition type between freshwater and marine environments. We monitored dissolved methane concentrations in three different water bodies (Lena River, Tiksi Bay, and Lake Golzovoye, Siberia, Russia) over a period of 2 years. Sampling was carried out under ice cover (April) and in open water (July–August). The methane oxidation (MOX) rate and the fractional turnover rate (k′) in water and melted ice samples from the late winter of 2017 was determined with the radiotracer method. In the Lena River winter methane concentrations were a quarter of the summer concentrations (8 nmol L -1 vs. 31 nmol L -1), and mean winter MOX rate was low (0.023 nmol L -1 d -1). In contrast, Tiksi Bay winter methane concentrations were 10 times higher than in summer (103 nmol L -1 vs. 13 nmol L -1). Winter MOX rates showed a median of 0.305 nmol L -1 d -1. In Lake Golzovoye, median methane concentrations in winter were 40 times higher than in summer (1957 nmol L -1 vs. 49 nmol L -1). However, MOX was much higher in the lake (2.95 nmol L -1 d -1) than in either the river or bay. The temperature had a strong influence on the MOX (Q10=2.72±0.69). In summer water temperatures ranged from 7–14 ∘ C and in winter from -0.7 to 1.3 ∘ C. In the ice cores a median methane concentration of 9 nM was observed, with no gradient between the ice surface and the bottom layer at the ice–water interface. MOX in the (melted) ice cores was mostly below the detection limit. Comparing methane concentrations in the ice with the underlaying water column revealed methane concentration in the water column 100–1000 times higher. The winter situation seemed to favor a methane accumulation under ice, especially in the lake with a stagnant water body. While on the other hand, in the Lena River with its flowing water, no methane accumulation under ice was observed. In a changing, warming Arctic, a shorter ice cover period is predicted. With respect to our study this would imply a shortened time for methane to accumulate below the ice and a shorter time for the less efficient winter MOX. Especially for lakes, an extended time of ice-free conditions could reduce the methane flux from the Arctic water bodies. [ABSTRACT FROM AUTHOR]

Lakes are vulnerable to climate change, and warming rates in the Arctic are faster than anywhere on Earth. Fishes are sensitive to changing temperatures, which directly control physiological processes. Food availability should partly dictate responses to climate change because energetic demands change with temperature, but few studies have simultaneously examined temperature and food availability.We used a fully factorial experiment to test effects of food availability and temperature (7.6, 12.7, and 17.4°C; 50 days) on growth, consumption, respiration, and excretion, and effects of temperature (12 and 19.3°C; 27 days) on habitat use and growth of a common, but understudied, mid‐level consumer, slimy sculpin Cottus cognatus, in arctic lakes. We also used bioenergetics modelling to predict consumptive demand under future warming scenarios.Growth rates were 3.4× higher at 12.7°C in high food compared to low food treatments, but the magnitude of differences depended on temperature. Within low food treatments, there was no statistical difference in growth rates among temperatures, suggesting food limitation. Consumption, respiration, and nitrogen excretion increased with temperature independent of food availability. Lower growth rates coincided with lower phosphorus excretion at the highest temperature, suggesting that fish selectively retained phosphorus at high temperatures and low food. In habitat choice experiments, fish were more likely to use the 12°C side of the tank, closely matching their optimal temperature. We predicted a 9% increase in consumption is required to maintain observed growth under a 4°C warming scenario.These results highlight considering changes in food resources and other associated indirect effects (e.g. excretion) that accompany changing temperatures with climate change. Depending on how food webs respond to warming, fish may cope with predicted warming if density‐dependent feedback maintains population sizes. [ABSTRACT FROM AUTHOR]

In contrast to temperate systems, Arctic lagoons that span the Alaska Beaufort Sea coast face extreme seasonality. Nine months of ice cover up to ∼1.7 m thick is followed by a spring thaw that introduces an enormous pulse of freshwater, nutrients, and organic matter into these lagoons over a relatively brief 2–3 week period. Prokaryotic communities link these subsidies to lagoon food webs through nutrient uptake, heterotrophic production, and other biogeochemical processes, but little is known about how the genomic capabilities of these communities respond to seasonal variability. Replicate water samples from two lagoons and one coastal site near Kaktovik, AK were collected in April (full ice cover), June (ice break up), and August (open water) to represent winter, spring, and summer, respectively. Samples were size fractionated to distinguish free-living and particle-attached microbial communities. Multivariate analysis of metagenomes indicated that seasonal variability in gene abundances was greater than variability between size fractions and sites, and that June differed significantly from the other months. Spring (June) gene abundances reflected the high input of watershed-sourced nutrients and organic matter via spring thaw, featuring indicator genes for denitrification possibly linked to greater organic carbon availability, and genes for processing phytoplankton-derived organic matter associated with spring blooms. Summer featured fewer indicator genes, but had increased abundances of anoxygenic photosynthesis genes, possibly associated with elevated light availability. Winter (April) gene abundances suggested low energy inputs and autotrophic bacterial metabolism, featuring indicator genes for chemoautotrophic carbon fixation, methane metabolism, and nitrification. Winter indicator genes for nitrification belonged to Thaumarchaeota and Nitrosomonadales, suggesting these organisms play an important role in oxidizing ammonium during the under-ice period. This study shows that high latitude estuarine microbial assemblages shift metabolic capabilities as they change phylogenetic composition between these extreme seasons, providing evidence that these communities may be resilient to large hydrological events in a rapidly changing Arctic. [ABSTRACT FROM AUTHOR]