Nature Geoscience, Published online: 15 June 2026; doi:10.1038/s41561-026-02013-1 While most newly formed organic carbon in the dark ocean is derived from chemolithoautotrophic microorganisms, 17% also comes from an alternative pathway called anaplerosis that is related to the tricarboxylic acid cycle, according to multi-omics datasets and single-cell analysis.