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1. Carbon dioxide fluxes of Arctic coastal ecosystems controlled by seasonal patterns of land‐to‐ocean connectivity

   https://doi.org/10.1002/lno.70101  

   Spera, Alina_C; Lougheed, Vanessa_L (June 2025, Limnology and Oceanography)

   Abstract The strength of coastal Arctic Ocean CO₂uptake is vulnerable to landscape‐scale changes such as hydrological intensification, changing climate, and alterations to terrestrial and aquatic biogeochemistry. Across a period of 4 yr (2019–2023) and three distinct sampling periods, we visited five coastal ecosystems of the Beaufort Sea with varying barrier island coverage to understand drivers of Arctic coastal CO₂flux. The ice cover sampling period was characterized by the highest pCO₂saturation and dissolved O₂undersaturation. We observed a > 100μatm difference in pCO₂over shallow depths (up to 2 m) at 73% of ice‐cover site visits. Notably, the geomorphology of barrier islands and channels controlled the flushing of colder Beaufort Sea waters across the systems and influenced the strength and appearance of both vertical thermohaline and pCO₂stratification. The ice breakup period reflected spring freshet and was a net CO₂sink during sampling, likely related to freshwater riverine dilution, CaCO₃dissolution from sea ice melt, and water column algal activity. During the open water sampling period, the interaction of marine and terrestrial contributions predicted the strength of the CO₂efflux, with freshwater inputs introducing higher temperatures and organic material, which increased remineralization. The capacity of these systems to act as CO₂sources or sinks varies throughout the year and is largely driven by geomorphic conditions. Any spatially integrative studies of CO₂flux or coastal productivity should consider the physical and biogeochemical heterogeneity of Arctic coastal ecosystems. 

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2. CO ₂ Emissions From Low Order Tundra Streams Stimulated by Surface‐Subsurface Connectivity Following Extreme Rainfall Events

   https://doi.org/10.1029/2024JG008459  

   Spera, Alina C; Lougheed, Vanessa L (May 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract Increases to summer Arctic rainfall and tundra thermal degradation are altering hydrological cycling in coastal watersheds with implications for carbon (C) cycling and transport of C to the atmosphere and coast. Arctic riverine research has focused on large rivers; however, small streams contribute significantly to vertical and longitudinal carbon dioxide (CO₂) fluxes. Despite the well‐established connection between hydrology and biogeochemistry, the impact of extreme rainfall events on Arctic aquatic C cycling remains a knowledge gap. This study characterized how hydrology, biogeochemistry, and geomorphology control the supply of CO₂to low order streams and their propensity to act as atmospheric CO₂sources. We characterize biogeochemical and hydrologic processes in unique reaches from a beaded stream and stream impacted by thermal erosion. Rainfall and its resulting increases to terrestrial‐aquatic connectivity drove the movement of CO₂and biodegradable dissolved organic C (BDOC) from soils into streams, however, BDOC mineralization only contributed a small portion of surface CO₂fluxes. Rain events likely stimulated stream benthic respiration, which led to CO₂contributions from net ecosystem production often exceeding surface CO₂fluxes and downstream CO₂transport. In addition, thermal degradation played a role in terrestrial‐aquatic connectivity of the streams. The erosion‐affected stream had inconsistent and smaller inputs of CO₂, had weaker heterotrophic conditions, and smaller CO₂emissions. Understanding how hydrologic regime, influenced by late summer rain events and stream morphology, controls the transport of CO₂and metabolism in small tundra streams will help improve predictions of landscape scale CO₂emissions from these critically understudied systems. 

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3. Carbon uptake in Eurasian boreal forests dominates the high‐latitude net ecosystem carbon budget

   https://doi.org/10.1111/gcb.16553  

   Watts, Jennifer D.; Farina, Mary; Kimball, John S.; Schiferl, Luke D.; Liu, Zhihua; Arndt, Kyle A.; Zona, Donatella; Ballantyne, Ashley; Euskirchen, Eugénie S.; Parmentier, Frans‐Jan W.; et al (January 2023, Global Change Biology)

   Abstract Arctic‐boreal landscapes are experiencing profound warming, along with changes in ecosystem moisture status and disturbance from fire. This region is of global importance in terms of carbon feedbacks to climate, yet the sign (sink or source) and magnitude of the Arctic‐boreal carbon budget within recent years remains highly uncertain. Here, we provide new estimates of recent (2003–2015) vegetation gross primary productivity (GPP), ecosystem respiration (R_eco), net ecosystem CO₂exchange (NEE;R_eco − GPP), and terrestrial methane (CH₄) emissions for the Arctic‐boreal zone using a satellite data‐driven process‐model for northern ecosystems (TCFM‐Arctic), calibrated and evaluated using measurements from >60 tower eddy covariance (EC) sites. We used TCFM‐Arctic to obtain daily 1‐km²flux estimates and annual carbon budgets for the pan‐Arctic‐boreal region. Across the domain, the model indicated an overall average NEE sink of −850 Tg CO₂‐C year⁻¹. Eurasian boreal zones, especially those in Siberia, contributed to a majority of the net sink. In contrast, the tundra biome was relatively carbon neutral (ranging from small sink to source). Regional CH₄emissions from tundra and boreal wetlands (not accounting for aquatic CH₄) were estimated at 35 Tg CH₄‐C year⁻¹. Accounting for additional emissions from open water aquatic bodies and from fire, using available estimates from the literature, reduced the total regional NEE sink by 21% and shifted many far northern tundra landscapes, and some boreal forests, to a net carbon source. This assessment, based on in situ observations and models, improves our understanding of the high‐latitude carbon status and also indicates a continued need for integrated site‐to‐regional assessments to monitor the vulnerability of these ecosystems to climate change. 

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4. Salinity and Moisture Influence CO ₂ and CH ₄ Emissions From High‐Latitude Coastal Soils

   https://doi.org/10.1029/2024JG008629  

   Barr, B_N; Kelsey, K_C; Leffler, A_J; Petit_Bon, M.; Beard, K_H (July 2025, Journal of Geophysical Research: Biogeosciences)

   Abstract Sea level rise and more frequent and larger storms will increase saltwater flooding in coastal terrestrial ecosystems, altering soil‐atmosphere CO₂and CH₄exchange. Understanding these impacts is particularly relevant in high‐latitude coastal soils that hold large carbon stocks but where the interaction of salinity and moisture on greenhouse gas flux remains unexplored. Here, we quantified the effects of salinity and moisture on CO₂and CH₄fluxes from low‐Arctic coastal soils from three landscape positions (two Wetlands and Upland Tundra) distinguished by elevation, flooding frequency, soil characteristics, and vegetation. We used a full factorial laboratory incubation experiment of three soil moisture levels (40%, 70%, or 100% saturation) and four salinity levels (freshwater, 3, 6, or 12 ppt). Salinity and soil moisture were important controls on CO₂and CH₄emissions across all landscape positions. In saturated soil, CO₂emissions increased with salinity in the lower elevation landscape positions but not in the Upland Tundra soil. Saturated soil was necessary for large CH₄emissions. CH₄emissions were greatest with low salinity, or after 11 weeks of incubation when SO₄²⁻was exhausted allowing for methanogenesis as the dominant mechanism of anaerobic respiration. In partially saturated soil, greater salinity suppressed CO₂production in all soils. CH₄fluxes were overall quite low, but increased between 3 and 6 ppt in the Tundra. In the future, a small increase in floodwater salinity may increase CO₂production while suppressing CH₄production; however, where water is impounded, CH₄production could become large, particularly in the landscapes most likely to flood. 

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5. Goose grubbing and warming suppress summer net ecosystem CO₂ uptake differentially across high‐Arctic tundra habitats

   https://doi.org/10.1002/ecy.4498  

   Petit_Bon, Matteo; Beard, Karen_H; Bråthen, Kari_Anne; Lee, Hanna; Jónsdóttir, Ingibjörg_S (December 2024, Ecology)

   Abstract Environmental changes, such as climate warming and higher herbivory pressure, are altering the carbon balance of Arctic ecosystems; yet, how these drivers modify the carbon balance among different habitats remains uncertain. This hampers our ability to predict changes in the carbon sink strength of tundra ecosystems. We investigated how spring goose grubbing and summer warming—two key environmental‐change drivers in the Arctic—alter CO₂fluxes in three tundra habitats varying in soil moisture and plant‐community composition. In a full‐factorial experiment in high‐Arctic Svalbard, we simulated grubbing and warming over two years and determined summer net ecosystem exchange (NEE) alongside its components: gross ecosystem productivity (GEP) and ecosystem respiration (ER). After two years, we found net CO₂uptake to be suppressed by both drivers depending on habitat. CO₂uptake was reduced by warming in mesic habitats, by warming and grubbing in moist habitats, and by grubbing in wet habitats. In mesic habitats, warming stimulated ER (+75%) more than GEP (+30%), leading to a 7.5‐fold increase in their CO₂source strength. In moist habitats, grubbing decreased GEP and ER by ~55%, while warming increased them by ~35%, with no changes in summer‐long NEE. Nevertheless, grubbing offset peak summer CO₂uptake and warming led to a twofold increase in late summer CO₂source strength. In wet habitats, grubbing reduced GEP (−40%) more than ER (−30%), weakening their CO₂sink strength by 70%. One‐year CO₂‐flux responses were similar to two‐year responses, and the effect of simulated grubbing was consistent with that of natural grubbing. CO₂‐flux rates were positively related to aboveground net primary productivity and temperature. Net ecosystem CO₂uptake started occurring above ~70% soil moisture content, primarily due to a decline in ER. Herein, we reveal that key environmental‐change drivers—goose grubbing by decreasing GEP more than ER and warming by enhancing ER more than GEP—consistently suppress net tundra CO₂uptake, although their relative strength differs among habitats. By identifying how and where grubbing and higher temperatures alter CO₂fluxes across the heterogeneous Arctic landscape, our results have implications for predicting the tundra carbon balance under increasing numbers of geese in a warmer Arctic. 

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