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1. A comparative analysis of the organic and inorganic carbon content of Halimeda and Penicillus (Chlorophyta, Bryopsidales) in a coastal subtropical lagoon

   https://doi.org/10.1515/bot-2018-0095  

   Hatt, Danielle Catherine; Collado-Vides, Ligia (August 2019, Botanica Marina)

   Abstract Standing stocks of the calcifying algae, Halimeda and Penicillus , have remained stable over the 10 years surveyed (2007–2017) in Florida Bay (USA), a subtropical lagoon. The maximum contribution of calcium carbonate (CaCO 3 ; 779.75 g m −2 ) was lower compared to tropical lagoons. Halimeda was more abundant and had higher inorganic:organic carbon ratios compared to Penicillus . The abundance of Penicillus varied across the surveyed sites, Sprigger Bank, Bob Allen Keys, and Duck Key, while its inorganic:organic carbon ratios did not vary significantly. Our long-term study provides a critical baseline that can help understand fluctuations in carbonate sediment production by calcareous algae in subtropical coastal waters. 

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2. Subducted organic matter buffered by marine carbonate rules the carbon isotopic signature of arc emissions

   https://doi.org/10.1038/s41467-022-30421-5  

   Tumiati, S.; Recchia, S.; Remusat, L.; Tiraboschi, C.; Sverjensky, D. A.; Manning, C. E.; Vitale Brovarone, A.; Boutier, A.; Spanu, D.; Poli, S. (December 2022, Nature Communications)

   Abstract Ocean sediments consist mainly of calcium carbonate and organic matter (phytoplankton debris). Once subducted, some carbon is removed from the slab and returns to the atmosphere as CO 2 in arc magmas. Its isotopic signature is thought to reflect the bulk fraction of inorganic (carbonate) and organic (graphitic) carbon in the sedimentary source. Here we challenge this assumption by experimentally investigating model sediments composed of 13 C-CaCO 3  +  12 C-graphite interacting with water at pressure, temperature and redox conditions of an average slab–mantle interface beneath arcs. We show that oxidative dissolution of graphite is the main process controlling the production of CO 2 , and its isotopic composition reflects the CO 2 /CaCO 3 rather than the bulk graphite/CaCO 3 (i.e., organic/inorganic carbon) fraction. We provide a mathematical model to relate the arc CO 2 isotopic signature with the fluid–rock ratios and the redox state in force in its subarc source. 

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3. Natural and Anthropogenic Drivers of Acidification in Large Estuaries

   https://doi.org/10.1146/annurev-marine-010419-011004  

   Cai, Wei-Jun; Feely, Richard A.; Testa, Jeremy M.; Li, Ming; Evans, Wiley; Alin, Simone R.; Xu, Yuan-Yuan; Pelletier, Greg; Ahmed, Anise; Greeley, Dana J.; et al (January 2021, Annual Review of Marine Science)

   Oceanic uptake of anthropogenic carbon dioxide (CO 2 ) from the atmosphere has changed ocean biogeochemistry and threatened the health of organisms through a process known as ocean acidification (OA). Such large-scale changes affect ecosystem functions and can have impacts on societal uses, fisheries resources, and economies. In many large estuaries, anthropogenic CO 2 -induced acidification is enhanced by strong stratification, long water residence times, eutrophication, and a weak acid–base buffer capacity. In this article, we review how a variety of processes influence aquatic acid–base properties in estuarine waters, including coastal upwelling, river–ocean mixing, air–water gas exchange, biological production and subsequent aerobic and anaerobic respiration, calcium carbonate (CaCO 3 ) dissolution, and benthic inputs. We emphasize the spatial and temporal dynamics of partial pressure of CO 2 ( pCO 2 ), pH, and calcium carbonate mineral saturation states. Examples from three large estuaries—Chesapeake Bay, the Salish Sea, and Prince William Sound—are used to illustrate how natural and anthropogenic processes and climate change may manifest differently across estuaries, as well as the biological implications of OA on coastal calcifiers. 

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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. Myriad Mapping of nanoscale minerals reveals calcium carbonate hemihydrate in forming nacre and coral biominerals

   https://doi.org/10.1038/s41467-024-46117-x  

   Schmidt, Connor A.; Tambutté, Eric; Venn, Alexander A.; Zou, Zhaoyong; Castillo Alvarez, Cristina; Devriendt, Laurent S.; Bechtel, Hans A.; Stifler, Cayla A.; Anglemyer, Samantha; Breit, Carolyn P.; et al (February 2024, Nature Communications)

   Abstract Calcium carbonate (CaCO₃) is abundant on Earth, is a major component of marine biominerals and thus of sedimentary and metamorphic rocks and it plays a major role in the global carbon cycle by storing atmospheric CO₂into solid biominerals. Six crystalline polymorphs of CaCO₃are known—3 anhydrous: calcite, aragonite, vaterite, and 3 hydrated: ikaite (CaCO₃·6H₂O), monohydrocalcite (CaCO₃·1H₂O, MHC), and calcium carbonate hemihydrate (CaCO₃·½H₂O, CCHH). CCHH was recently discovered and characterized, but exclusively as a synthetic material, not as a naturally occurring mineral. Here, analyzing 200 million spectra with Myriad Mapping (MM) of nanoscale mineral phases, we find CCHH and MHC, along with amorphous precursors, on freshly deposited coral skeleton and nacre surfaces, but not on sea urchin spines. Thus, biomineralization pathways are more complex and diverse than previously understood, opening new questions on isotopes and climate. Crystalline precursors are more accessible than amorphous ones to other spectroscopies and diffraction, in natural and bio-inspired materials. 

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