Microscale drivers of summer CO2 fluxes in the Svalbard High Arctic tundra

High-Arctic ecosystems are strongly affected by climate change, and it is still unclear whether they will become a carbon source or sink in the next few decades. In turn, such knowledge gaps on the drivers and the processes controlling CO2 fluxes and storage make future projections of the Arctic carbon budget a challenging goal. During summer 2019, we extensively measured CO2 fluxes at the soil–vegetation–atmosphere interface, together with basic meteoclimatic variables and ecological characteristics in the Bayelva river basin near Ny Ålesund, Spitzbergen, Svalbard (NO). By means of multi-regression models, we identified the main small-scale drivers of CO2 emission (Ecosystem Respiration, ER), and uptake (Gross Primary Production, GPP) in this tundra biome, showing that (i) at point scale, the temporal variability of fluxes is controlled by the classical drivers, i.e. air temperature and solar irradiance respectively for ER and GPP, (ii) at site scale, the heterogeneity of fractional vegetation cover, soil moisture and vegetation type acted as additional source of variability for both CO2 emissions and uptake. The assessment of the relative importance of such drivers in the multi-regression model contributes to a better understanding of the terrestrial carbon dioxide exchanges and of Critical Zone processes in the Arctic tundra.

What do caribou eat? A review of the literature on caribou diet

Historically the study of diet caribou and reindeer (Rangifer tarandus (Gmelin, 1788)) has been specific to herds and few comprehensive circumpolar analyses of Rangifer diet exist. As a result, the importance of certain diet items may play an outsized role in the caribou diet zeitgeist, e.g., lichen. It is incumbent to challenge this notion and test the relevant importance of various diet items within the context of prevailing hypotheses. We provide a systematic overview of 30 caribou studies reporting caribou diet and test biologically relevant hypotheses about spatial and temporal dietary variation. Our results indicate that in the winter caribou primarily consume lichen, but in warmer seasons, and primary productivity is lower, caribou primarily consume graminoids and other vascular plants. In more productive environments, where caribou have more competitors and predators, consumption of lichen increased. Overall, our description of caribou diet reveals that caribou diet is highly variable, but in circumstances where they can consume vascular plants, they will. As climate change affects Boreal and Arctic ecosystems, the type and volume of food consumed by caribou has become an increasingly important focus for conservation and management of caribou.

Nutrient pathways and their susceptibility to past and future change in the Eurasian Arctic Ocean

Climate change is altering nutrient cycling within the Arctic Ocean, having knock-on effects to Arctic ecosystems. Primary production in the Arctic is principally nitrogen-limited, particularly in the western Pacific-dominated regions where denitrification exacerbates nitrogen loss. The nutrient status of the eastern Eurasian Arctic remains under debate. In the Barents Sea, primary production has increased by 88% since 1998. To support this rapid increase in productivity, either the standing stock of nutrients has been depleted, or the external nutrient supply has increased. Atlantic water inflow, enhanced mixing, benthic nitrogen cycling, and land–ocean interaction have the potential to alter the nutrient supply through addition, dilution or removal. Here we use new datasets from the Changing Arctic Ocean program alongside historical datasets to assess how nitrate and phosphate concentrations may be changing in response to these processes. We highlight how nutrient dynamics may continue to change, why this is important for regional and international policy-making and suggest relevant research priorities for the future.

Inuvialuit Knowledge of Pacific Salmon Range Expansion in the Western Canadian Arctic

Rapid climate change is altering Arctic ecosystems and significantly affecting the livelihoods and cultural traditions of Arctic Indigenous peoples. In the Inuvialuit Settlement Region (ISR), an increase in the harvest of Pacific salmon indicates largescale changes influencing Inuvialuit fisheries. In this project we recorded and synthesized Inuvialuit knowledge of Pacific salmon. We conducted 54 interviews with Inuvialuit fishers about the history of Pacific salmon harvest, how it has changed in recent decades, and concurrent changes to local environments and fish species. Our interviews show that historic, incidental salmon harvest in the ISR ranged from infrequent to common among western communities, but was rare or unprecedented among eastern communities. Participants in all six communities reported a recent increase in salmon harvest and attributed this shift to regional environmental change. Fishers were concerned that salmon would negatively affect their cultural traditions and preferred fish species. Given uncertainty about the effects of salmon on local fisheries, research on salmon diets in the Arctic, their subsidies to Arctic freshwater systems, and the likelihood of their establishment is vital.

Pollution in the Arctic Ocean: An overview of multiple pressures and implications for ecosystem services

The Arctic is undergoing unprecedented change. Observations and models demonstrate significant perturbations to the physical and biological systems. Arctic species and ecosystems, particularly in the marine environment, are subject to a wide range of pressures from human activities, including exposure to a complex mixture of pollutants, climate change and fishing activity. These pressures affect the ecosystem services that the Arctic provides. Current international policies are attempting to support sustainable exploitation of Arctic resources with a view to balancing human wellbeing and environmental protection. However, assessments of the potential combined impacts of human activities are limited by data, particularly related to pollutants, a limited understanding of physical and biological processes, and single policies that are limited to ecosystem-level actions. This manuscript considers how, when combined, a suite of existing tools can be used to assess the impacts of pollutants in combination with other anthropogenic pressures on Arctic ecosystems, and on the services that these ecosystems provide. Recommendations are made for the advancement of targeted Arctic research to inform environmental practices and regulatory decisions.

Influence of diesel fuel on the composition and content of free amino acids in the green alga Acrosiphonia arcta

Arctic ecosystems are the most sensitive and vulnerable to anthropogenic impact, namely, the influence of petroleum products. The aim is to identify the effect of diesel fuel (DF) on the composition of free amino acids (FAA) in Acrosiphonia arcta in Barents Sea. The impact of DF concentrations of 20 - 3000 maximal permitted concentration (MPC) was analyzed. It was found that A. arcta contains 20 amino acids, 16 of which are proteinogenic and 8 are essential. The composition of the FAA pool did not change under the influence of DF, but the content of individual FAA and their total amount differed. The ratio of the dominant amino acids changes: at concentrations of DF up to 1000 MPC content of proline increased, and decreased at higher concentrations of DF. Under the influence of DF in concentration of 3000 MPC, taurine content significant increased. The least negative effect was exerted under the influence of DF concentration of 20 MPC, more significant - at the concentration more than 1000 MPC. Changes in the content of FAA are probably associated with the redirection of the synthesis pathways of amino acid groups, as well as the inhibitory effect of the toxicant on protein synthesis.

Methane in Zackenberg Valley, NE Greenland: multidecadal growing season fluxes of a high-Arctic tundra

The carbon balance of high-latitude terrestrial ecosystems plays an essential role in the atmospheric concentration of trace gases, including carbon dioxide (CO2) and methane (CH4). Increasing atmospheric methane levels have contributed to ∼ 20 % of the observed global warming since the pre-industrial era. Rising temperatures in the Arctic are expected to promote the release of methane from Arctic ecosystems. Still, existing methane flux measurement efforts are sparse and highly scattered, and further attempts to assess the landscape fluxes over multiple years are needed. Here we combine multi-year July–August methane flux monitoring (2006–2019) from automated flux chambers in the central fens of Zackenberg Valley, northeast Greenland, with several flux measurement campaigns on the most common vegetation types in the valley to estimate the landscape fluxes over 14 years. Methane fluxes based on manual chamber measurements are available from campaigns in 1997, 1999–2000, and in shorter periods from 2007–2013 and were summarized in several published studies. The landscape fluxes are calculated for the entire valley floor and a smaller subsection of the valley floor, containing the productive fen area, Rylekærene. When integrated for the valley floor, the estimated July–August landscape fluxes were low compared to the single previous estimate, while the landscape fluxes for Rylekærene were comparable to previous estimates. The valley floor was a net methane source during July–August, with estimated mean methane fluxes ranging from 0.18 to 0.67 mg m−2 h−1. The mean methane fluxes in the fen-rich Rylekærene were substantially higher, with fluxes ranging from 0.98 to 3.26 mg m−2 h−1. A 2017–2018 erosion event indicates that some fen and grassland areas in the center of the valley are becoming unstable following pronounced fluvial erosion and a prolonged period of permafrost warming. Although such physical disturbance in the landscape can disrupt the current ecosystem–atmosphere flux patterns, even pronounced future erosion of ice-rich areas is unlikely to impact methane fluxes on a landscape scale significantly. Instead, projected changes in future climate in the valley play a more critical role. The results show that multi-year landscape methane fluxes are highly variable on a landscape scale and stress the need for long-term spatially distributed measurements in the Arctic.

3. Arctic ecosystems

‘Arctic ecosystems’ highlights the treeless landscapes that fringe the Arctic Ocean, in which the diversity of plants is low, nutrient supply is limited, and soil depth is constrained by permafrost. The aim is to capture some of the key characteristics of the Arctic biome in the past and present. How do ecosystems function in the northern high latitudes? How have they responded to the recent environmental change? Arctic vegetation is grouped into twenty-one provinces based on various characteristics including relative uniformity of species and number of endemics. High fluctuation in animal populations is a key feature of the Arctic biome.

Carbon response of tundra ecosystems to advancing greenup and snowmelt in Alaska

The ongoing disproportionate increases in temperature and precipitation over the Arctic region may greatly alter the latitudinal gradients in greenup and snowmelt timings as well as associated carbon dynamics of tundra ecosystems. Here we use remotely-sensed and ground-based datasets and model results embedding snowmelt timing in phenology at seven tundra flux tower sites in Alaska during 2001–2018, showing that the carbon response to early greenup or delayed snowmelt varies greatly depending upon local climatic limits. Increases in net ecosystem productivity (NEP) due to early greenup were amplified at the higher latitudes where temperature and water strongly colimit vegetation growth, while NEP decreases due to delayed snowmelt were alleviated by a relief of water stress. Given the high likelihood of more frequent delayed snowmelt at higher latitudes, this study highlights the importance of understanding the role of snowmelt timing in vegetation growth and terrestrial carbon cycles across warming Arctic ecosystems.

Mammoths Lost Their Steppe Habitat to Climate Change

Ancient plant and animal DNA buried in Arctic sediments preserve a 50,000-year history of Arctic ecosystems, suggesting that climate change contributed to mammoth extinction.