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1. Contribution of gas concentration and transfer velocity to CO₂ flux variability in northern lakes

   https://doi.org/10.1002/lno.12528  

   Rudberg, David; Schenk, Jonathan; Pajala, Gustav; Sawakuchi, Henrique; Sieczko, Anna; Sundgren, Ingrid; Duc, Nguyen Thanh; Karlsson, Jan; MacIntyre, Sally; Melack, John; et al (April 2024, Limnology and Oceanography)

   Abstract The CO₂flux () from lakes to the atmosphere is a large component of the global carbon cycle and depends on the air–water CO₂concentration gradient (ΔCO₂) and the gas transfer velocity (k). Both ΔCO₂andkcan vary on multiple timescales and understanding their contributions to is important for explaining variability in fluxes and developing optimal sampling designs. We measured and ΔCO₂and derivedkfor one full ice‐free period in 18 lakes using floating chambers and estimated the contributions of ΔCO₂andkto variability. Generally,kcontributed more than ΔCO₂to short‐term (1–9 d) variability. With increased temporal period, the contribution ofkto variability decreased, and in some lakes resulted in ΔCO₂contributing more thankto variability over the full ice‐free period. Increased contribution of ΔCO₂to variability over time occurred across all lakes but was most apparent in large‐volume southern‐boreal lakes and in deeper (> 2 m) parts of lakes, whereaskwas linked to variability in shallow waters. Accordingly, knowing the variability of bothkand ΔCO₂over time and space is needed for accurate modeling of from these variables. We conclude that priority in assessments should be given to direct measurements of at multiple sites when possible, or otherwise from spatially distributed measurements of ΔCO₂combined withk‐models that incorporate spatial variability of lake thermal structure and meteorology. 

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2. ND70 Series Basaltic Glass Reference Materials for Volatile Element ( H₂O , CO₂ , S, Cl, F) Measurement and the C Ionisation Efficiency Suppression Effect of Water in Silicate Glasses in SIMS

   https://doi.org/10.1111/ggr.12572  

   Moussallam, Yves; Towbin, William Henry; Plank, Terry; Bureau, Hélène; Khodja, Hicham; Guan, Yunbin; Ma, Chi; Baker, Michael B; Stolper, Edward M; Naab, Fabian U; et al (July 2024, Geostandards and Geoanalytical Research)

   We present a new set of reference materials, the ND70‐series, forin situmeasurement of volatile elements (H₂O, CO₂, S, Cl, F) in silicate glass of basaltic composition. The materials were synthesised in piston cylinders at pressures of 1 to 1.5 GPa under volatile‐undersaturated conditions. They span mass fractions from 0 to 6%m/mH₂O, from 0 to 1.6%m/mCO₂and from 0 to 1%m/mS, Cl and F. The materials were characterised by elastic recoil detection analysis for H₂O, by nuclear reaction analysis for CO₂, by elemental analyser for CO₂, by Fourier transform infrared spectroscopy for H₂O and CO₂, by secondary ion mass spectrometry for H₂O, CO₂, S, Cl and F, and by electron probe microanalysis for CO₂, S, Cl and major elements. Comparison between expected and measured volatile amounts across techniques and institutions is excellent. It was found however that SIMS measurements of CO₂mass fractions using either Cs⁺or O⁻primary beams are strongly affected by the glass H₂O content. Reference materials have been made available to users at ion probe facilities in the US, Europe and Japan. Remaining reference materials are preserved at the Smithsonian National Museum of Natural History where they are freely available on loan to any researcher. 

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3. neonSoilFlux: An R package for continuous sensor‐based estimation of soil CO₂ fluxes

   https://doi.org/10.1111/2041-210x.70216  

   Zobitz, John; Ayres, Edward; Werbin, Zoey; Abdi, Ridwan; Ashburner‐Wright, Natalie; Brown, Lillian; Frink‐Sobierajski, Ryan; Lee, Lajntxiag; Mehmeti, Dijonë; Tran, Christina; et al (December 2025, Methods in Ecology and Evolution)

   Abstract Accurate quantification of soil carbon fluxes is essential to reduce uncertainty in estimates of the terrestrial carbon sink. However, these fluxes vary over time and across ecosystem types and so, it can be difficult to estimate them accurately across large scales. The flux‐gradient method estimates soil carbon fluxes using co‐located measurements of soil CO₂concentration, soil temperature, soil moisture and other soil properties. The National Ecological Observatory Network (NEON) provides such data across 20 ecoclimatic domains spanning the continental U.S., Puerto Rico, Alaska and Hawai‘i.We present an R software package (neonSoilFlux) that acquires soil environmental data to compute half‐hourly soil carbon fluxes for each soil replicate plot at a given terrestrial NEON site. To assess the computed fluxes, we visited six focal NEON sites and measured soil carbon fluxes using a closed‐dynamic chamber approach.Outputs from theneonSoilFluxshowed agreement with measured fluxes (R²between measured andneonSoilFluxoutputs ranging from 0.12 to 0.77 depending on calculation method used); measured outputs generally fell within the range of calculated uncertainties from the gradient method. Calculated fluxes fromneonSoilFluxaggregated to the daily scale exhibited expected site‐specific seasonal patterns.While the flux‐gradient method is broadly effective, its accuracy is highly sensitive to site‐specific inputs, including the extent to which gap‐filing techniques are used to interpolate missing sensor data and to estimates of soil diffusivity and moisture content. Future refinement and validation ofneonSoilFluxoutputs can contribute to existing databases of soil carbon flux measurements, providing near real‐time estimates of a critical component of the terrestrial carbon cycle. 

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4. Sub‐Daily Variations in Tree Xylem Water Isotopic Compositions in a Temperate Northeastern US Forest

   https://doi.org/10.1002/hyp.70137  

   Tierney, Kiernan; Sobota, Matthew; Snarski, Josh; Li, Kevin; Knighton, James (April 2025, Hydrological Processes)

   ABSTRACT Sampling of stable isotopes in plant xylem water (δ²H, δ¹⁸O) has become a ubiquitous technique to study spatiotemporal variations in the water taken up by plant roots; however, open questions remain concerning the most appropriate time of day to sample trees to obtain representative xylem water isotopic values (δ_XYLEM). We sampled the δ_XYLEMof oak and maple trees prior to solar midday (i.e., in a recommended sampling window) and then again after solar midday (i.e., outside of the recommended window) across 4 months. The paired root mean squared difference between AM and PM δ¹⁸O ranged from 1.00‰ to 1.16‰ for maples and 0.23‰ to 2.55‰ for oaks across all sampling dates. Xylem water seasonal origin index (SOI) values derived from AM and PM δ_XYLEMsamples were significantly different, though both SOI estimates supported the conclusion that maple and oak δ_XYLEMreflected summer precipitation on all sampling dates. We conclude that sampling time of day is a significant consideration in the design of δ_XYLEMsampling campaigns; however, our findings also support flexibility in the collection time of δ_XYLEMin field sites where sampling during the optimal time of day is challenging. 

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5. Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems

   https://doi.org/10.1029/2023JG007638  

   Treat, Claire C; Virkkala, Anna‐Maria; Burke, Eleanor; Bruhwiler, Lori; Chatterjee, Abhishek; Fisher, Joshua B; Hashemi, Josh; Parmentier, Frans‐Jan W; Rogers, Brendan M; Westermann, Sebastian; et al (March 2024, Journal of Geophysical Research: Biogeosciences)

   Abstract Significant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO₂and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO₂sink with lower net CO₂uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO₂sink was located in western Canada (median: −52 g C m⁻² y⁻¹) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m⁻² y⁻¹). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH₄m⁻² y⁻¹). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO₂and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects. 

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