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The effects of climate change on plants are particularly pronounced in the Arctic region. Warming relaxes the temperature and nutrients boundaries that limit tundra plant growth. Increased resource availability under future climate conditions may induce a shift from a conservative economic strategy to an acquisitive one. Following the leaf economics spectrum that hypothesizes a strategy gradient between survival, plant size and costs for the photosynthetic leaf area, light absorption of tundra plants may increase. We investigated climate change effects on light absorptance and the relationship between light absorptance (fraction of absorbed photosynthetically active radiation, FAPAR) and structural and nutritional leaf traits, performing a soil warming and surface soil fertilization experiment on two deciduous tundra shrub species. Our results show that fertilization and warming combined increase light absorptance in Arctic shrubs and that FAPAR is correlated with leaf nutrients but not with structural leaf traits. This indicates an economic strategy shift of shrubs from conservative to acquisitive induced by warming and fertilization combined. We found species‐specific differences: FAPAR was influenced by warming alone in Betula nana but not in Salix pulchra, and FAPAR was correlated with leaf phosphorus in B. nana but not in S. pulchra. We attribute this to water limitation of B. nana that generally grows in drier areas within the study site compared to S. pulchra. We conclude that FAPAR is a measure that opens up more possibilities to estimate nutritional leaf traits and nutrient cycles, plant economic strategies, and ecological feedbacks of the tundra ecosystem on broader scales. Plain Language Summary: The effects of climate change on plants are very strong in the Arctic. Tundra plants are usually limited by temperature and nutrients. Tundra plants usually have an energy saving strategy, with long lifespan and small leaves. A warmer environment with more nutrients may shift their strategy to faster growth, larger leaves, and more light absorption. We examined climate change effects on the light absorptance of two tundra shrubs. In order to do this, we made an experiment in which we warmed and fertilized the soil. We furthermore studied the relationship between light absorptance and plant traits. Our results show that fertilization and warming combined increase light absorptance in Arctic shrubs. Furthermore, we could show that light absorptance is strongly related to the concentration of nutrients in the leaves. We also found differences in light absorptance between the two shrub species. We believe that these differences are due to Betula nana growing in drier areas with less water compared to Salix pulchra. We think that light absorptance is a good measure for predicting changes in nutrient cycles and plant strategies in the tundra ecosystem. Key Points: Fertilization and warming combined increase light absorptance in two deciduous Arctic shrub species. This indicates an economic strategy shiftLight absorptance is correlated with leaf nutrients but not with structural leaf traits in Arctic shrubsThere are species‐specific differences between the shrub species in regard to light absorptance [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]

Climate change in the Arctic leads to permafrost degradation and to associated changes in freshwater geochemistry. There is a limited understanding of how disturbances such as active layer detachments or retrogressive thaw slumps impact water quality on a catchment scale. This study investigates how permafrost degradation affects concentrations of dissolved organic carbon (DOC), total dissolved solids (TDS), suspended sediment, and stable water isotopes in adjacent Low Arctic watersheds. We incorporated data on disturbance between 1952 and 2015, as well as sporadic runoff and geochemistry data of streams nearby. Our results show that the total disturbed area decreased by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66% in all six catchments. The spatial variability of hydrochemical parameters is linked to catchment properties and not necessarily reflected at the outflow. Degrading ice‐wedge polygons were found to increase DOC concentrations upstream in Ice Creek West, whereas hydrologically connected disturbances were linked to increases in TDS and suspended sediment. Although we found a great spatial variability of hydrochemical concentrations along the paired watershed, there was a linear relationship between catchment size and daily DOC, total dissolved nitrogen, and TDS fluxes for all six streams. Suspended sediment flux on the contrary did not show a clear relationship as one hydrologically connected retrogressive thaw slump impacted the overall flux in one of the streams. Understanding the spatial variability of water quality will help to model the lateral geochemical fluxes from Arctic catchments. Plain Language Summary: One effect climate change has in the Arctic is the thawing of permafrost. Permafrost is defined as ground that remains below 0 °C for at least two consecutive years. The low temperatures in the High North lead to very slow decomposition rates of organic material from plants and animals. A lot of this material has accumulated over thousands of years. As air temperatures in the Arctic are rising, permafrost is thawing. This is also termed permafrost degradation. It can occur in two forms: (1) The gradual deeper thawing of permafrost is called thermal perturbation. It might lead to a subsidence (sinking) of the ground, because water that was previously frozen runs off. (2) Thawing of the ground may lead to a destabilization of the ground and connected landslides. This is termed physical or surface disturbance. These two forms of permafrost degradation have an impact on the water quality of rivers flowing through the terrain. In this study, we investigated the impacts of permafrost degradation on stream hydrochemistry on Herschel Island, Yukon Territory, Canada. We identified active physical disturbances in the past using aerial photographs from 1952 and 1970 and satellites images from 2011 and 2015. This was done for the areas from which rainwater flows into the same river (catchment area) of six streams named Water Creek, Beach Creek, Fox Creek, Ice Creek West, Ice Creek East, and Eastern Gully. In 2016, we collected water samples along two neighboring streams (Ice Creek West and Ice Creek East) to compare the impacts of local physical disturbances on the hydrochemistry. In these two streams, we also measured water flow (discharge) during the monitoring season. We further collected samples at the outflow of the other four streams nearby. Water samples were analyzed in the laboratory for different chemical properties that help us to understand the influence of permafrost degradation. For the six streams, we found that the total disturbed area decreased by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66%. We were able to link permafrost degradation to changes in chemical water composition within the two neighboring streams. It is important that disturbances are "hydrologically connected" to impact concentrations of inorganic compounds (total dissolved solids) and mud (suspended sediment) in the streams. Essentially, this means that water needs to flow through these disturbances to mobilize the material and influence the concentration in the stream. Taking all studied streams together, the overall flux of dissolved organic carbon, total dissolved solids, and total dissolved nitrogen (i.e., the amount of chemical compound [in kg] transported away in every liter of river water) depends on catchment size. The larger the catchment, the more of this material is transported away. This relationship could not be confirmed for suspended sediment, because a hydrologically connected retrogressive thaw slump heavily impacted the flux in one of the streams. This study is important because the river water ultimately drains into the Arctic Ocean and might change the water quality there. This may have consequences for the animals and plants living in the ocean. We need to understand the influence of permafrost degradation on stream water quality to assess future changes of the Arctic Ocean. Key Points: Between 1952 and 2015, the total disturbed area decreased by 41%, and the number of disturbances increased by 66%Hydrological connectivity of permafrost disturbances is essential to impact suspended sediment and solute concentrations in the streamThere is a linear relationship between catchment size and daily flux of dissolved organic carbon, total dissolved nitrogen, and solutes [ABSTRACT FROM AUTHOR]