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1. Summertime Evolution of Net Community Production and CO ₂ Flux in the Western Arctic Ocean

   https://doi.org/10.1029/2020GB006651  

   Ouyang, Zhangxian; Qi, Di; Zhong, Wenli; Chen, Liqi; Gao, Zhongyong; Lin, Hongmei; Sun, Heng; Li, Tao; Cai, Wei‐Jun (March 2021, Global Biogeochemical Cycles)

   Abstract To examine seasonal and regional variabilities in metabolic status and the coupling of net community production (NCP) and air‐sea CO₂fluxes in the western Arctic Ocean, we collected underway measurements of surface O₂/Ar and partial pressure of CO₂(pCO₂) in the summers of 2016 and 2018. With a box‐model, we demonstrate that accounting for local sea ice history (in addition to wind history) is important in estimating NCP from biological oxygen saturation (Δ(O₂/Ar)) in polar regions. Incorporating this sea ice history correction, we found that most of the western Arctic exhibited positive Δ(O₂/Ar) and negativepCO₂saturation, Δ(pCO₂), indicative of net autotrophy but with the relationship between the two parameters varying regionally. In the heavy ice‐covered areas, where air‐sea gas exchange was suppressed, even minor NCP resulted in relatively high Δ(O₂/Ar) and lowpCO₂in water due to limited gas exchange. Within the marginal ice zone, NCP and CO₂flux magnitudes were strongly inversely correlated, suggesting an air to sea CO₂flux induced primarily by biological CO₂removal from surface waters. Within ice‐free waters, the coupling of NCP and CO₂flux varied according to nutrient supply. In the oligotrophic Canada Basin, NCP and CO₂flux were both small, controlled mainly by air‐sea gas exchange. On the nutrient‐rich Chukchi Shelf, NCP was strong, resulting in great O₂release and CO₂uptake. This regional overview of NCP and CO₂flux in the western Arctic Ocean, in its various stages of ice‐melt and nutrient status, provides useful insight into the possible biogeochemical evolution of rapidly changing polar oceans. 

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2. Electrochemical CO ₂ Reduction in the Presence of Impurities: Influences and Mitigation Strategies

   https://doi.org/10.1002/anie.202213782  

   Harmon, Nia J.; Wang, Hailiang (November 2022, Angewandte Chemie International Edition)

   Abstract The electrochemical conversion of waste CO₂into useful fuels and chemical products is a promising approach to reduce CO₂emissions; however, several challenges still remain to be addressed. Thus far, most CO₂reduction studies use pure CO₂as the gas reactant, but CO₂emissions typically contain a number of gas impurities, such as nitrogen oxides, oxygen gas, and sulfur oxides. Gas impurities in CO₂can pose a significant obstacle for efficient CO₂electrolysis because they can influence the reaction and catalyst. This Minireview highlights early examples of CO₂reduction studies using mixed‐gas feeds, explores strategies to sustain CO₂reduction in the presence of gas impurities, and discusses their implications for future progress in this emerging field. 

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3. Improving Predictions of Stream CO ₂ Concentrations and Fluxes Using a Stream Network Model: A Case Study in the East River Watershed, CO, USA

   https://doi.org/10.1029/2021GB006972  

   Saccardi, Brian; Winnick, Matthew (December 2021, Global Biogeochemical Cycles)

   Abstract Inland waters are an important component of the global carbon budget. However, our ability to predict carbon fluxes from stream systems remains uncertain, aspCO₂varies within streams at scales of 1–100 m. This makes direct monitoring of large‐scale CO₂fluxes impractical. We incorporate CO₂input and output fluxes into a stream network advection‐reaction model, representing the first process‐based representation of stream CO₂dynamics at watershed scales. This model includes groundwater (GW) CO₂inputs, water column (WC), benthic hyporheic zone (BHZ) respiration, downstream advection, and atmospheric exchange. We evaluate this model against existing statistical methods including upscaling and multiple linear regressions through comparisons to high‐resolution streampCO₂data collected across the East River Watershed in the Colorado Rocky Mountains (USA). The stream network model accurately captures GW, evasion, and respiration‐drivenpCO₂variability and significantly outperforms multiple linear regressions for predictingpCO₂. Further, the model provides estimates of CO₂contributions from internal versus external sources suggesting that streams transition from GW‐ to BHZ‐dominated sources between 3rd and 4th Strahler orders, with GW, BHZ, and WC accounting for 49.3%, 50.6%, and 0.1% of CO₂fluxes from the watershed, respectively. Lastly, stream network model atmospheric CO₂fluxes are 4‐12x times smaller than upscaling technique predictions, largely due to relationships between streampCO₂and gas exchange velocities. Taken together, this stream network model improves our ability to predict stream CO₂dynamics and efflux. Furthermore, future applications to regional and global scales may result in a significant downward revision of global flux estimates. 

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4. Lotic‐SIPCO2 : Adaptation of an open‐source CO₂ sensor system and examination of associated emission uncertainties across a range of stream sizes and land uses

   https://doi.org/10.1002/lom3.10600  

   Robison, Andrew L.; Koenig, Lauren E.; Potter, Jody D.; Snyder, Lisle E.; Hunt, Christopher W.; McDowell, William H.; Wollheim, Wilfred M. (February 2024, Limnology and Oceanography: Methods)

   Abstract River networks play a crucial role in the global carbon cycle, as relevant sources of carbon dioxide (CO₂) to the atmosphere. Advancements in high‐frequency monitoring in aquatic environments have enabled measurement of dissolved CO₂concentration at temporal resolutions essential for studying carbon variability and evasion from these dynamic ecosystems. Here, we describe the adaptation, deployment, and validation of an open‐source and relatively low‐cost in situpCO₂sensor system for lotic ecosystems, the lotic‐SIPCO2. We tested the lotic‐SIPCO2 in 10 streams that spanned a range of land cover and basin size. Key system adaptations for lotic environments included prevention of biofouling, configuration for variable stage height, and reduction of headspace equilibration time. We then examined which input parameters contribute the most to uncertainty in estimating CO₂emission rates and found scaling factors related to the gas exchange velocity were the most influential when CO₂concentration was significantly above saturation. Near saturation, sensor measurement ofpCO₂contributed most to uncertainty in estimating CO₂emissions. We also found high‐frequency measurements ofpCO₂were not necessary to accurately estimate median emission rates given the CO₂regimes of our streams, but daily to weekly sampling was sufficient. High‐frequency measurements ofpCO₂remain valuable for exploring in‐stream metabolic variability, source partitioning, and storm event dynamics. Our adaptations to the SIPCO2 offer a relatively affordable and robust means of monitoring dissolved CO₂in lotic ecosystems. Our findings demonstrate priorities and related considerations in the design of monitoring projects of dissolved CO₂and CO₂evasion dynamics more broadly. 

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5. Co/Co ₂ P Nanoparticles Encapsulated within Hierarchically Porous Nitrogen, Phosphorus, Sulfur Co‐doped Carbon as Bifunctional Electrocatalysts for Rechargeable Zinc‐Air Batteries

   https://doi.org/10.1002/celc.202101246  

   Wang, Likai; Sun, Yinggang; Zhang, Shenzhi; Di, Hexiang; Liu, Qiming; Du, Xin; Li, Zhongfang; Yang, Kai; Chen, Shaowei (November 2021, ChemElectroChem)

   Abstract Developing high performance nonprecious metal‐based electrocatalysts has become a critical first step towards commercial applications of metal‐air batteries. Herein, nanocomposites based on Co/Co₂P nanoparticles encapsulated within hierarchically porous N, P, S co‐doped carbon are prepared by controlled pyrolysis of zeolitic imidazolate frameworks (ZIF‐67) and poly(cyclotriphosphazene‐co‐4,4’‐sulfonyldiphenol) (PZS). The resulting Co/Co₂P@NPSC nanocomposites exhibit apparent oxygen reduction reaction (ORR) and evolution reaction (OER) catalytic performance, and are used as the reversible oxygen catalyst for zinc‐air batteries (ZABs). Density functional theory (DFT) calculations exhibit that Co₂P could provide active sites for the ORR and promote the conversion between the adsorbed intermediates, and porous N,P,S co‐doped carbon with Co₂P nanoparticles also improves the exposure of actives sites and endows charge transport. Liquid‐state ZABs with Co/Co₂P@NPSC as the cathode catalysts demonstrate the greater power density of 198.1 mW cm⁻²and a long cycling life of 50 h at 10 mA cm⁻², likely due to the encapsulation of Co/Co₂P nanoparticles by the carbon shell. Solid‐state ZABs also display a remarkable performance with a high peak power density of 74.3 mW cm⁻². Therefore, this study indicates the meaning of the design and engineering of hierarchical porous carbon nanomaterial as electrocatalyst for rechargeable metal‐air batteries. 

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