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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. 

Abstract Tropical cyclones erode and remobilize coastal sediments but their impact on the deep ocean remains unclear. Hurricane‐driven transport of carbonates and associated materials from reef carbonate platforms to the deep ocean has important implications for carbon storage, deep ecosystems and ocean chemistry as carbonate platform reef‐sourced aragonite and high‐Mg calcite (HMC) may dissolve and contribute to deep water total alkalinity. Here we describe two hurricane‐driven resuspension events where deep sediment plumes from the Bermuda Pedestal (NW Atlantic) were advected to deep waters surrounding the Oceanic Flux Program (OFP) mooring site, ∼75 km southeast of Bermuda. Hurricanes Fabian (Cat. 3, 2003) and Igor (Cat. 1, 2010) generated large near‐inertial waves propagating to >750 m depths, leading to widespread sediment resuspension from the Pedestal. Following Fabian, carbonate fluxes at the OFP site increased 15‐fold, 32‐fold, and 6‐fold at 500, 1,500 and 3,200 m, respectively, with the 1,500 m flux equivalent to the total annual carbonate flux. OFP traps similarly captured a large detrital carbonate plume following Igor; here, the plume was shallower and persisted longer. Microscopy, geochemistry, and mineralogy confirmed that both plumes consisted of fine‐grained shallow‐water detrital carbonates alongside other materials accumulated on the Pedestal including phosphorus, lithogenic, authigenic, and pollutant elements. Clay‐sized particles (<4 μm) in both plumes exhibited high contents of lithogenic and authigenic elements, and Zn, Cd, and V, facilitating their transport over long distances. Grain‐size, elemental, and lipid composition indicated that plumes intercepted at different depths originated from different source areas on the Pedestal.