Authigenic carbonate in Japan Trench hadal sediments

A team led by researchers at Ocean University of China, with colleagues from institutions in China, the USA, Japan and Austria, reported widespread authigenic calcium carbonate buried in sediments of the Japan Trench hadal zone. The samples come from water depths of more than 7000 m. The study was published in Nature Communications on 3 November 2026. doi.org

Based on isotopic modeling, the authors estimate the flux of organic-carbon-derived carbonate in the Japan Trench at about 28.6 Tg C Myr–1. doi.org

Carbonate below the compensation depth

Shallow marine carbonates are recognized as key agents in deep carbon cycling. According to the authors, however, the formation and burial of carbonates below the carbonate compensation depth remain poorly understood. To address this, they investigated carbonates from the Japan Trench, using samples and data provided by the IODP. doi.org

The authors report depletions in both stable and radiocarbon isotopes in the authigenic carbonates. They interpret these as indicating an organic carbon (OC) source, likely delivered primarily by deep-sea landslides. doi.org Carbon isotopic measurements were carried out with the participation of NOSAMS and Ocean University of China, and synchrotron soft X-ray images were collected at the National Synchrotron Radiation Laboratory of China.

Subduction and the carbon sink

Isotopic modeling in the study suggests that subduction of these OC-derived carbonates can impart negative δ13C signatures to fluids released in the NE Japan subduction zone. doi.org

The authors propose that earthquake-driven influx of organic matter into the hadal zone may have facilitated sustained carbonate production. doi.org On this basis they describe OC-derived authigenic carbonates in hadal trenches as an underappreciated carbon sink and a potential mechanism for transferring organic carbon into the deep Earth. doi.org

The flux value is a model-based estimate for the Japan Trench, not a direct measurement. The conclusions about the landslide and earthquake origin of the organic carbon are the authors' interpretation of the isotopic data.

Authigenic carbonate found in Japan Trench sediments below 7000 m; flux estimated at 28.6 Tg C per Myr

Carbonate below the compensation depth

Subduction and the carbon sink

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