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1. Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

   https://doi.org/10.1029/2019JG005349  

   Breithaupt, Joshua L.; Smoak, Joseph M.; Bianchi, Thomas S.; Vaughn, Derrick R.; Sanders, Christian J.; Radabaugh, Kara R.; Osland, Michael J.; Feher, Laura C.; Lynch, James C.; Cahoon, Donald R.; et al (February 2020, Journal of Geophysical Research: Biogeosciences)

   Abstract Rates of organic carbon (OC) burial in some coastal wetlands appear to be greater in recent years than they were in the past. Possible explanations include ongoing mineralization of older OC or the influence of an unaccounted‐for artifact of the methods used to measure burial rates. Alternatively, the trend may represent real acceleration in OC burial. We quantified OC burial rates of mangrove and coastal freshwater marshes in southwest Florida through a comparison of rates derived from²¹⁰Pb,¹³⁷Cs, and surface marker horizons. Age/depth profiles of lignin: OC were used to assess whether down‐core remineralization had depleted the OC pool relative to lignin, and lignin phenols were used to quantify the variability of lignin degradation. Over the past 120 years, OC burial rates at seven sites increased by factors ranging from 1.4 to 6.2. We propose that these increases represent net acceleration. Change in relative sea‐level rise is the most likely large‐scale driver of acceleration, and sediment deposition from large storms can contribute to periodic increases. Mangrove sites had higher OC and lignin burial rates than marsh sites, indicating inherent differences in OC burial factors between the two habitat types. The higher OC burial rates in mangrove soils mean that their encroachment into coastal freshwater marshes has the potential to increase burial rates in those locations even more than might be expected from the acceleration trends. Regionally, these findings suggest that burial represents a substantially growing proportion of the coastal wetland carbon budget. 

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2. Quantifying erosion rates and weathering pathways that maximize soil organic carbon storage

   https://doi.org/10.1007/s10533-023-01054-7  

   Roering, Joshua J.; Hunter, Brooke D.; Ferrier, Ken L.; Chadwick, Oliver A.; Yoo, Kyungsoo; Wackett, Adrian A.; Almond, Peter C.; Silva, Lucas; Jellinek, A. Mark (June 2023, Biogeochemistry)
3. Photochemical dissolution of buoyant microplastics to dissolved organic carbon: Rates and microbial impacts

   https://doi.org/10.1016/j.jhazmat.2019.121065  

   Zhu, Lixin; Zhao, Shiye; Bittar, Thais B.; Stubbins, Aron; Li, Daoji (February 2020, Journal of Hazardous Materials)
4. Cycling Rates of Particulate Organic Carbon Along the GEOTRACES Pacific Meridional Transect GP15

   https://doi.org/10.1029/2023GB007940  

   Amaral, Vinícius J.; Lam, Phoebe J.; Marchal, Olivier; Kenyon, Jennifer A. (January 2024, Global Biogeochemical Cycles)

   Abstract Understanding particle cycling processes in the ocean is critical for predicting the response of the biological carbon pump to external perturbations. Here, measurements of particulate organic carbon (POC) concentration in two size fractions (1–51 and >51 μm) from GEOTRACES Pacific meridional transect GP15 are combined with a POC cycling model to estimate rates of POC production, (dis)aggregation, sinking, remineralization, and vertical transport mediated by migrating zooplankton, in the euphotic zone (EZ) and upper mesopelagic zone (UMZ) of distinct environments. We find coherent variations in POC cycling parameters and fluxes throughout the transect. Thus, the settling speed of POC in the >51 μm fraction increased with depth in the UMZ, presumably due to higher particle densities at depth. The settling flux of total POC (>1 μm) out of the EZ was positively correlated with primary production integrated over the EZ; the highest export occurred in the subarctic gyre while the lowest occurred in the subtropical gyres. The ratio of POC settling flux to integrated primary production was low (<5%) along GP15, which suggests an efficient recycling of POC in the EZ in all trophic regimes. Specific rates of POC remineralization did not show clear variations with temperature or dissolved oxygen concentration, that is, POC recycling was apparently controlled by other factors such as microbial colonization and substrate lability. Particle cohesiveness, as approximated by the second‐order rate constant for particle aggregation, was negatively correlated with trophic regime: particles appeared more cohesive in low‐productivity regions than in high‐productivity regions. 

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5. High rates of daytime river metabolism are an underestimated component of carbon cycling

   https://doi.org/10.1038/s43247-022-00607-2  

   Tromboni, Flavia; Hotchkiss, Erin R.; Schechner, Anne E.; Dodds, Walter K.; Poulson, Simon R.; Chandra, Sudeep (November 2022, Communications Earth & Environment)

   Abstract River metabolism and, thus, carbon cycling are governed by gross primary production and ecosystem respiration. Traditionally river metabolism is derived from diel dissolved oxygen concentrations, which cannot resolve diel changes in ecosystem respiration. Here, we compare river metabolism derived from oxygen concentrations with estimates from stable oxygen isotope signatures (δ¹⁸O₂) from 14 sites in rivers across three biomes using Bayesian inverse modeling. We find isotopically derived ecosystem respiration was greater in the day than night for all rivers (maximum change of 113 g O₂ m⁻² d⁻¹, minimum of 1 g O₂ m⁻² d⁻¹). Temperature (20 °C) normalized rates of ecosystem respiration and gross primary production were 1.1 to 87 and 1.5 to 22-fold higher when derived from oxygen isotope data compared to concentration data. Through accounting for diel variation in ecosystem respiration, our isotopically-derived rates suggest that ecosystem respiration and microbial carbon cycling in rivers is more rapid than predicted by traditional methods. 

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