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1. The Impact of Orbital Precession on Air‐Sea CO 2 Exchange in the Southern Ocean

   https://doi.org/10.1029/2023GL103820  

   Persch, Cole F. ; DiNezio, Pedro ; Lovenduski, Nicole S. ( October 2023 , Geophysical Research Letters)

   Orbital precession has been linked to glacial cycles and the atmospheric carbon dioxide (CO₂) concentration, yet the direct impact of precession on the carbon cycle is not well understood. We analyze output from an Earth system model configured under different orbital parameters to isolate the impact of precession on air‐sea CO₂flux in the Southern Ocean—a component of the global carbon cycle that is thought to play a key role on past atmospheric CO₂variations. Here, we demonstrate that periods of high precession are coincident with anomalous CO₂outgassing from the Southern Ocean. Under high precession, we find a poleward shift in the southern westerly winds, enhanced Southern Ocean meridional overturning, and an increase in the surface ocean partial pressure of CO₂along the core of the Antarctic Circumpolar Current. These results suggest that orbital precession may have played an important role in driving changes in atmospheric CO₂.

    

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2. Autonomous Wintertime Observations of Air‐Sea Exchange in the Gulf Stream Reveal a Perfect Storm for Ocean CO 2 Uptake

   https://doi.org/10.1029/2021GL096805  

   Nickford, S. ; Palter, J. B. ; Donohue, K. ; Fassbender, A. J. ; Gray, A. R. ; Long, J. ; Sutton, A. J. ; Bates, N. R. ; Takeshita, Y. ( March 2022 , Geophysical Research Letters)

   A scarcity of wintertime observations of surface ocean carbon dioxide partial pressure (pCO₂) in and near the Gulf Stream creates uncertainty in the magnitude of the regional carbon sink and its controlling mechanisms. Recent observations from an Uncrewed Surface Vehicle (USV), outfitted with a payload to measure surface ocean and lower atmospherepCO₂, revealed sharp gradients in oceanpCO₂across the Gulf Stream. Surface oceanpCO₂was lower by ∼50 μatm relative to the atmosphere in the subtropical mode water (STMW) formation region. This undersaturation combined with strong wintertime winds allowed for rapid ocean uptake of CO₂, averaging −11.5 mmol m⁻² day⁻¹during the February 2019 USV mission. The unique timing of this mission revealed active STMW formation. The USV proved to be a useful tool for CO₂flux quantification in the poorly observed, dynamic western boundary current environment.

    

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3. The ECCO‐Darwin Data‐Assimilative Global Ocean Biogeochemistry Model: Estimates of Seasonal to Multidecadal Surface Ocean p CO 2 and Air‐Sea CO 2 Flux

   https://doi.org/10.1029/2019MS001888  

   Carroll, D. ; Menemenlis, D. ; Adkins, J. F. ; Bowman, K. W. ; Brix, H. ; Dutkiewicz, S. ; Fenty, I. ; Gierach, M. M. ; Hill, C. ; Jahn, O. ; et al ( October 2020 , Journal of Advances in Modeling Earth Systems)

   Quantifying variability in the ocean carbon sink remains problematic due to sparse observations and spatiotemporal variability in surface oceanpCO₂. To address this challenge, we have updated and improved ECCO‐Darwin, a global ocean biogeochemistry model that assimilates both physical and biogeochemical observations. The model consists of an adjoint‐based ocean circulation estimate from the Estimating the Circulation and Climate of the Ocean (ECCO) consortium and an ecosystem model developed by the Massachusetts Institute of Technology Darwin Project. In addition to the data‐constrained ECCO physics, a Green's function approach is used to optimize the biogeochemistry by adjusting initial conditions and six biogeochemical parameters. Over seasonal to multidecadal timescales (1995–2017), ECCO‐Darwin exhibits broad‐scale consistency with observed surface oceanpCO₂and air‐sea CO₂flux reconstructions in most biomes, particularly in the subtropical and equatorial regions. The largest differences between CO₂uptake occur in subpolar seasonally stratified biomes, where ECCO‐Darwin results in stronger winter uptake. Compared to the Global Carbon Project OBMs, ECCO‐Darwin has a time‐mean global ocean CO₂sink (2.47 ± 0.50 Pg C year⁻¹) and interannual variability that are more consistent with interpolation‐based products. Compared to interpolation‐based methods, ECCO‐Darwin is less sensitive to sparse and irregularly sampled observations. Thus, ECCO‐Darwin provides a basis for identifying and predicting the consequences of natural and anthropogenic perturbations to the ocean carbon cycle, as well as the climate‐related sensitivity of marine ecosystems. Our study further highlights the importance of physically consistent, property‐conserving reconstructions, as are provided by ECCO, for ocean biogeochemistry studies.

    

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4. Impact of Circular, Waste-Heat Reuse Pathways on PM 2.5 -Air Quality, CO 2 Emissions, and Human Health in India: Comparison with Material Exchange Potential

   https://doi.org/10.1021/acs.est.1c05897  

   Lal, Raj M. ; Tibrewal, Kushal ; Venkataraman, Chandra ; Tong, Kangkang ; Fang, Andrew ; Ma, Qiao ; Wang, Shuxiao ; Kaiser, Jennifer ; Ramaswami, Anu ; Russell, Armistead G. ( June 2022 , Environmental Science & Technology)
5. Global Trends in Air‐Water CO 2 Exchange Over Seagrass Meadows Revealed by Atmospheric Eddy Covariance

   https://doi.org/10.1029/2020GB006848  

   Van Dam, Bryce ; Polsenaere, Pierre ; Barreras‐Apodaca, Aylin ; Lopes, Christian ; Sanchez‐Mejia, Zulia ; Tokoro, Tatsuki ; Kuwae, Tomohiro ; Loza, Lucia Gutiérrez ; Rutgersson, Anna ; Fourqurean, James ; et al ( April 2021 , Global Biogeochemical Cycles)

   Coastal vegetated habitats like seagrass meadows can mitigate anthropogenic carbon emissions by sequestering CO₂as “blue carbon” (BC). Already, some coastal ecosystems are actively managed to enhance BC storage, with associated BC stocks included in national greenhouse gas inventories. However, the extent to which BC burial fluxes are enhanced or counteracted by other carbon fluxes, especially air‐water CO₂flux (FCO₂) remains poorly understood. In this study, we synthesized all available direct FCO₂measurements over seagrass meadows made using atmospheric Eddy Covariance, across a globally representative range of ecotypes. Of the four sites with seasonal data coverage, two were net CO₂sources, with average FCO₂equivalent to 44%–115% of the global average BC burial rate. At the remaining sites, net CO₂uptake was 101%–888% of average BC burial. A wavelet coherence analysis demonstrated that FCO₂was most strongly related to physical factors like temperature, wind, and tides. In particular, tidal forcing was a key driver of global‐scale patterns in FCO₂, likely due to a combination of lateral carbon exchange, bottom‐driven turbulence, and pore‐water pumping. Lastly, sea‐surface drag coefficients were always greater than the prediction for the open ocean, supporting a universal enhancement of gas‐transfer in shallow coastal waters. Our study points to the need for a more comprehensive approach to BC assessments, considering not only organic carbon storage, but also air‐water CO₂exchange, and its complex biogeochemical and physical drivers.

    

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