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1. Biogenic carbon pool production maintains the Southern Ocean carbon sink

   https://doi.org/10.1073/pnas.2217909120  

   Huang, Yibin; Fassbender, Andrea J.; Bushinsky, Seth M. (April 2023, Proceedings of the National Academy of Sciences)

   Through biological activity, marine dissolved inorganic carbon (DIC) is transformed into different types of biogenic carbon available for export to the ocean interior, including particulate organic carbon (POC), dissolved organic carbon (DOC), and particulate inorganic carbon (PIC). Each biogenic carbon pool has a different export efficiency that impacts the vertical ocean carbon gradient and drives natural air–sea carbon dioxide gas (CO₂) exchange. In the Southern Ocean (SO), which presently accounts for ~40% of the anthropogenic ocean carbon sink, it is unclear how the production of each biogenic carbon pool contributes to the contemporary air–sea CO₂exchange. Based on 107 independent observations of the seasonal cycle from 63 biogeochemical profiling floats, we provide the basin-scale estimate of distinct biogenic carbon pool production. We find significant meridional variability with enhanced POC production in the subantarctic and polar Antarctic sectors and enhanced DOC production in the subtropical and sea-ice-dominated sectors. PIC production peaks between 47°S and 57°S near the “great calcite belt.” Relative to an abiotic SO, organic carbon production enhances CO₂uptake by 2.80 ± 0.28 Pg C y⁻¹, while PIC production diminishes CO₂uptake by 0.27 ± 0.21 Pg C y⁻¹. Without organic carbon production, the SO would be a CO₂source to the atmosphere. Our findings emphasize the importance of DOC and PIC production, in addition to the well-recognized role of POC production, in shaping the influence of carbon export on air–sea CO₂exchange. 

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2. Sediment Trap Studies to Understand the Oceanic Carbon Cycling: Significance of Resuspended Sediments

   https://doi.org/10.7850/jkso.2021.26.2.145  

   Kim, Minkyoung (April 2021, Bada Online)

   Choi, Man Sik (Ed.)

   For several decades, sediment traps have served as one of the key tools for constraining the biological carbon pump (BCP), a process that vertically exports particulate organic carbon (POC) and associated biogenic materials from marine primary production in surface waters to the deep ocean interior. In this paper, I introduced the general methods, the current status of global sediment trap studies, and importance of it to understand the deep ocean carbon cycling. Recent studies suggest that sinking POC in the deep ocean are more complex and spatio-temporally heterogeneous than we considered. Especially researches those studied resuspended and laterally transported particles are presented. Researches that used organic (radiocarbon; 14C) and inorganic (Al) tracers to understand the oceanic POC cycling and the significance of resuspended particles are reviewed, and the importance of radiocarbon study by using MICADAS (Mini radioCarbon Dating Systems) is emphasized. 

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3. Transmitted Cross-Polarized Light Detection of Particulate Inorganic Carbon Concentrations and Fluxes in the Ocean Water Column: Ships to ARGO Floats

   https://doi.org/10.3389/frsen.2022.837938  

   Bishop, James K.; Amaral, Vinicius J.; Lam, Phoebe J.; Wood, Todd J.; Lee, Jong-Mi; Laubach, Allison; Barnard, Andrew; Derr, Alex; Orrico, Cristina (March 2022, Frontiers in Remote Sensing)

   Particulate inorganic carbon (PIC) plays a major role in the ocean carbon cycle impacting pH, dissolved inorganic carbon, and alkalinity, as well as particulate organic carbon (POC) export and transfer efficiency to the deep sea. Remote sensing retrievals of PIC in surface waters span two decades, yet knowledge of PIC concentration variability in the water column is temporally and spatially limited due to a reliance on ship sampling. To overcome the space–time gap in observations, we have developed optical sensors for PIC concentration and flux that exploit the high mineral birefringence of CaCO 3 minerals, and thus enable real-time data when deployed operationally from ship CTDs and ARGO-style Carbon Flux Explorer floats. For PIC concentrations, we describe a fast (10 Hz) digital low-power (∼0.5 W) sensor that utilizes cross-polarized transmitted light to detect the photon yield from suspended birefringent particles in the water column. This sensor has been CTD-deployed to depths as great as 6,000 m and cross-calibrated against particulates sampled by large volume in situ filtration and CTD/rosettes. We report data from the September–November 2018 GEOTRACES GP15 meridional transect from the Aleutian Islands to Tahiti along 152°W where we validated two prototype sensors deployed on separate CTD systems surface to bottom at 39 stations, many of which were taken in nearly particle-free waters. We compare sensor results with major particle phase composition (particularly PIC and particulate aluminum) from simultaneously collected size-fractionated particulate samples collected by large volume in situ filtration. We also report results from the June 2017 California Current Ecosystem-Long Term Ecological Research (CCE-LTER) process study in California coastal waters where high PIC levels were found. We demonstrate that the PIC concentration sensor can detect PIC concentration variability from 0.01 to >1 μM in the water column (except in nepheloid layers) and outline engineering needs and progress on its integration with the Carbon Flux Explorer, an autonomous float. 

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4. Microzooplankton grazing on the coccolithophore Emiliania huxleyi and its role in the global calcium carbonate cycle

   https://doi.org/10.1126/sciadv.adr5453  

   Dean, Chloe L; Harvey, Elizabeth L; Johnson, Matthew D; Subhas, Adam V (November 2024, Science Advances)

   Identifying mechanisms driving the substantial dissolution of biogenic CaCO₃(60 to 80%) in surface and mesopelagic waters of the global ocean is critical for constraining the surface ocean’s alkalinity and inorganic carbon budgets. We examine microzooplankton grazing on coccolithophores, photosynthetic calcifying algae responsible for a majority of open-ocean CaCO₃production, as a mechanism driving shallow dissolution. We show that microzooplankton grazing dissolves 92 ± 7% of ingested coccolith calcite, which may explain 50 to 100% of the observed CaCO₃dissolution in supersaturated surface waters. Microzooplankton grazing on coccolithophores is thus a substantial, previously unrecognized biological mechanism affecting the ballasting of organic carbon to deeper waters, the ecology and fitness of microzooplankton themselves due to buffering of food vacuole pH, and ultimately the continued ability of the surface ocean to take up atmospheric carbon dioxide. 

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5. Characterization of Sinking Particulate Organic Carbon Biogeochemical Variability in the Santa Barbara Basin via Solid State 13C NMR

   Chaza, T; Coli, N; Gao, X; Masiello, CA; Benitez-Nelson, CR (February 2026, American Geophysical Union)

   Particulate organic carbon (POC) includes suspended and sinking particles ≥ 0.2 μm, and can consist of microbial detritus, fecal pellets, and terrestrially derived organic material. The bulk chemical characterization of this material has been challenging historically because many approaches are destructive, limiting the number of measurements possible. Here we report data on the seasonal and depth-dependent variability in the POC organic geochemistry in the Santa Barbara Basin (off the coast of California) using solid-state 13C nuclear magnetic resonance (13C NMR), a non-destructive approach. NMR can provide bulk information on the overall chemical characteristics of entire samples. In the case of sinking marine POC, this information can be obtained without chemical pretreatment or destructive analyses of any kind. Here we show that there is significant variation in the bulk chemistry of sinking POC in the Santa Barbara Basin, consistent with changes in surface ecology, decomposition of organic matter, and seasonal delivery of terrestrial material by aerosol and by rivers. This study evaluates how seasonality impacts exported POC by tracking terrestrial inputs during flood or fire events across El Niño-Southern Oscillation (ENSO) phases. The Santa Barbara Basin sediment traps have been deployed since 1993 and offer a long, high-resolution flux record. Using solid-state 13C NMR, we studied sinking POC samples collected bi-weekly from June 2015 to April 2017, a period that included an intense El Niño event. We estimated molecular composition using NMR functional group data and an end-member molecular mixing model (MMM), which reports virtual concentrations of lipids, lignin, protein, carbohydrates, and black carbon. Preliminary MMM results indicate samples have a higher proportion of aromatic C than typical open-ocean POC, indicating more fire-derived black carbon during the El Niño phase. Such detailed molecular insights will impact blue carbon accounting and climate mitigation strategies. 

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