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Abstract Carbonate‐brucite chimneys are a characteristic of low‐ to moderate‐temperature, ultramafic‐hosted alkaline hydrothermal systems, such as the Lost City hydrothermal field located on the Atlantis Massif at 30°N near the Mid‐Atlantic Ridge. These chimneys form as a result of mixing between warm, serpentinization‐derived vent fluids and cold seawater. Previous work has documented the evolution in mineralogy and geochemistry associated with the aging of the chimneys as hydrothermal activity wanes. However, little is known about spatial heterogeneities within and among actively venting chimneys. New mineralogical and geochemical data (87Sr/86Sr and stable C, O, and clumped isotopes) indicate that the brucite and calcite precipitate at elevated temperatures in vent fluid‐dominated domains in the interior of chimneys. Exterior zones dominated by seawater are brucite‐poor and aragonite is the main carbonate mineral. Carbonates record mostly out of equilibrium oxygen and clumped isotope signatures due to rapid precipitation upon vent fluid‐seawater mixing. On the other hand, the carbonates precipitate closer to carbon isotope equilibrium, with dissolved inorganic carbon in seawater as the dominant carbon source and have δ13C values within the range of marine carbonates. Our data suggest that calcite is a primary mineral in the active hydrothermal chimneys and does not exclusively form as a replacement of aragonite during later alteration with seawater. Elevated formation temperatures and lower87Sr/86Sr relative to aragonite in the same sample suggest that calcite may be the first carbonate mineral to precipitate.
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This content will become publicly available on June 2, 2026
Fish Carbonates in the North Atlantic and Their Potential Role in the Carbon Cycle
Abstract Marine fish precipitate carbonates in their intestines that they subsequently excrete as part of an osmoregulatory strategy. While fish carbonates are proposed to be volumetrically significant to the global carbonate budget, no study has presented direct evidence of fish carbonates in the open ocean. Here we examine sediment trap material collected by the Oceanic Flux Program (OFP) in the North Atlantic and observe the episodic occurrence of enigmatic blue particles since 1992. The blue particles are comprised of calcite with unusually high magnesium content (up to 46 mol%) with distinctively depleted δ13C and enriched δ18O compared with calcite produced by common marine calcifiers. Based on the mineralogical, isotopic, and textural similarities between the blue particles and fish carbonates, we propose that the blue particles are produced by pelagic fish. Our data suggest that fish modify their intestinal fluids to create a concentrated, highly supersaturated,13C depleted solution capable of precipitating calcite with high magnesium content and low δ13C. Collectively, our data imply that fish carbonate production is an open‐ocean phenomenon, opening up the possibility that fish contribute to the production, dissolution, and export of carbonates globally.
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- PAR ID:
- 10659371
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 39
- Issue:
- 6
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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