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1. Gelatinous Zooplankton‐Mediated Carbon Flows in the Global Oceans: A Data‐Driven Modeling Study

   https://doi.org/10.1029/2020GB006704  

   Luo, Jessica Y. ; Condon, Robert H. ; Stock, Charles A. ; Duarte, Carlos M. ; Lucas, Cathy H. ; Pitt, Kylie A. ; Cowen, Robert K. ( September 2020 , Global Biogeochemical Cycles)

   Among marine organisms, gelatinous zooplankton (GZ; cnidarians, ctenophores, and pelagic tunicates) are unique in their energetic efficiency, as the gelatinous body plan allows them to process and assimilate high proportions of oceanic carbon. Upon death, their body shape facilitates rapid sinking through the water column, resulting in carcass depositions on the seafloor (“jelly‐falls”). GZ are thought to be important components of the biological pump, but their overall contribution to global carbon fluxes remains unknown. Using a data‐driven, three‐dimensional, carbon cycle model resolved to a 1° global grid, with a Monte Carlo uncertainty analysis, we estimate that GZ consumed 7.9–13 Pg C y⁻¹in phytoplankton and zooplankton, resulting in a net production of 3.9–5.8 Pg C y⁻¹in the upper ocean (top 200 m), with the largest fluxes from pelagic tunicates. Non‐predation mortality (carcasses) comprised 25% of GZ production, and combined with the much greater fecal matter flux, total GZ particulate organic carbon (POC) export at 100 m was 1.6–5.2 Pg C y⁻¹, equivalent to 32–40% of the global POC export. The fast sinking GZ export resulted in a high transfer efficiency (T_eff) of 38–62% to 1,000 m and 25–40% to the seafloor. Finally, jelly‐falls at depths >50 m are likely unaccounted for in current POC flux estimates and could increase benthic POC flux by 8–35%. The significant magnitude of and distinct sinking properties of GZ fluxes support a critical yet underrecognized role of GZ carcasses and fecal matter to the biological pump and air‐sea carbon balance.

    

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2. Global Trends in the Distribution of Biogenic Minerals in the Ocean

   https://doi.org/10.1029/2022JC019470  

   Subhas, Adam V. ; Pavia, Frank J. ; Dong, Sijia ; Lam, Phoebe J. ( February 2023 , Journal of Geophysical Research: Oceans)

   The cycling of marine particulate matter is critical for sequestering carbon in the deep ocean and in marine sediments. Biogenic minerals such as calcium carbonate (CaCO₃) and opal add density to more buoyant organic material, facilitating particle sinking and export. Here, we compile and analyze a global data set of particulate organic carbon (POC), particulate inorganic carbon (PIC, or CaCO₃), and biogenic silica (bSi, or opal) concentrations collected using large volume pumps (LVPs). We analyze the distribution of all three biogenic phases in the small (1–53 μm) and large (>53 μm) size classes. Over the entire water column 76% of POC exists in the small size fraction. Similarly, the small size class contains 82% of PIC, indicating the importance of small‐sized coccolithophores to the PIC budget of the ocean. In contrast, 50% of bSi exists in the large size fraction, reflecting the larger size of diatoms and radiolarians compared with coccolithophores. We use PIC:POC and bSi:POC ratios in the upper ocean to document a consistent signal of shallow mineral dissolution, likely linked to biologically mediated processes. Sediment trap PIC:POC and bSi:POC are elevated with respect to LVP samples and increase strongly with depth, indicating the concentration of mineral phases and/or a deficit of POC in large sinking particles. We suggest that future sampling campaigns pair LVPs with sediment traps to capture the full particulate field, especially the large aggregates that contribute to mineral‐rich deep ocean fluxes, and may be missed by LVPs.

    

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3. Simulations With the Marine Biogeochemistry Library (MARBL)

   https://doi.org/10.1029/2021MS002647  

   Long, Matthew C. ; Moore, J. Keith ; Lindsay, Keith ; Levy, Michael ; Doney, Scott C. ; Luo, Jessica Y. ; Krumhardt, Kristen M. ; Letscher, Robert T. ; Grover, Maxwell ; Sylvester, Zephyr T. ( November 2021 , Journal of Advances in Modeling Earth Systems)

   The Marine Biogeochemistry Library (MARBL) is a prognostic ocean biogeochemistry model that simulates marine ecosystem dynamics and the coupled cycles of carbon, nitrogen, phosphorus, iron, silicon, and oxygen. MARBL is a component of the Community Earth System Model (CESM); it supports flexible ecosystem configuration of multiple phytoplankton and zooplankton functional types; it is also portable, designed to interface with multiple ocean circulation models. Here, we present scientific documentation of MARBL, describe its configuration in CESM2 experiments included in the Coupled Model Intercomparison Project version 6 (CMIP6), and evaluate its performance against a number of observational data sets. The model simulates present‐day air‐sea CO₂flux and many aspects of the carbon cycle in good agreement with observations. However, the simulated integrated uptake of anthropogenic CO₂is weak, which we link to poor thermocline ventilation, a feature evident in simulated chlorofluorocarbon distributions. This also contributes to larger‐than‐observed oxygen minimum zones. Moreover, radiocarbon distributions show that the simulated circulation in the deep North Pacific is extremely sluggish, yielding extensive oxygen depletion and nutrient trapping at depth. Surface macronutrient biases are generally positive at low latitudes and negative at high latitudes. CESM2 simulates globally integrated net primary production (NPP) of 48 Pg C yr⁻¹and particulate export flux at 100 m of 7.1 Pg C yr⁻¹. The impacts of climate change include an increase in globally integrated NPP, but substantial declines in the North Atlantic. Particulate export is projected to decline globally, attributable to decreasing export efficiency associated with changes in phytoplankton community composition.

    

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4. Annual Net Community Production of Particulate and Dissolved Organic Carbon From a Decade of Biogeochemical Profiling Float Observations in the Northeast Pacific

   https://doi.org/10.1029/2020GB006599  

   Haskell, II, W. Z. ; Fassbender, A. J. ; Long, J. S. ; Plant, J. N. ( October 2020 , Global Biogeochemical Cycles)

   Carbon export out of the surface ocean via the biological pump is a critical sink for atmospheric carbon dioxide. This process transports organic carbon to the deep ocean through sinking particulate organic carbon (POC) and the downward transport of suspended POC and dissolved organic carbon (DOC). Changes in the relative contribution of each pathway can significantly affect the magnitude and efficiency of carbon export to depth. Net community production (NCP), an analog of carbon export under steady state assumptions, is typically estimated using budgets of biologically important chemical tracers in the upper ocean constrained by ship‐board or autonomous platform observations. In this study, we use measurements from biogeochemical profiling floats, the Ocean Station Papa mooring, and recently developed algorithms for carbonate system parameters to constrain budgets for three tracers (nitrate, dissolved inorganic carbon, and total alkalinity) and estimate NCP in the Northeast Pacific from 2009 to 2017. Using our multiple‐tracer approach, and constraining end‐member nutrient ratios of the POC and DOC produced, we not only calculate regional NCP throughout the annual cycle and across multiple depth horizons, but also partition this quantity into particulate and dissolved portions. We also use a particle backscatter‐based approach to estimate POC attenuation with depth and present a new method to constrain particle export across deeper horizons and estimate in situ export efficiency. Our results agree well with previously published estimates of regional carbon export annually and suggest that the approaches presented here could be used to assess the magnitude and efficiency of carbon export in other regions of the world's oceans.

    

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5. Dynamics of the Marine Dissolved Organic Carbon Reservoir in Glacial Climate Simulations: The Importance of Biological Production

   https://doi.org/10.1029/2022PA004522  

   Gilchrist, Maya D. ; Matsumoto, Katsumi ( July 2023 , Paleoceanography and Paleoclimatology)

   The marine dissolved organic carbon (DOC) reservoir rivals the atmospheric carbon inventory in size. Recent work has suggested that the size of the DOC reservoir may respond to variations in sea temperature and global overturning circulation strength. Moreover, mobilization of marine DOC has been implicated in paleoclimate events including Cryogenian glaciation and Eocene hyperthermals. Despite these suggestions, the dynamics of the marine DOC reservoir are poorly understood, and previous carbon cycle modeling has generally assumed this reservoir to be static. In this study, we utilize an Earth system model of intermediate complexity to assess the response of the marine DOC reservoir to various glacial boundary conditions. Our results indicate that the marine DOC reservoir is responsive to glacial perturbations and may shrink or expand on the order of 10–100 Pg C. In contrast to recent studies that emphasize the importance of DOC degradation in driving the mobility of DOC reservoir, our study indicates the importance of DOC production. In the experiment under full glacial boundary conditions, for example, a 19% drop in net primary production leads to an 81 Pg C reduction in the DOC pool, without which the atmospheric CO₂concentration would have been lower by approximately 38 ppm by dissolved inorganic carbon changes alone. Thus, DOC reservoir variability is necessary to fully account for the simulated changes in atmospheric CO₂concentration. Our findings based on glacial experiments are corroborated in a different set of simulations using freshwater flux to induce weakening of the Atlantic meridional overturning circulation.

    

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