Marine sediments are vast, underexplored habitats and represent one of the largest carbon deposits on our planet. Microbial communities drive nutrient cycling in these sediments, but the full extent of their taxonomic and metabolic diversity remains to be explored. Here, we analysed shallow coastal and deep subseafloor sediment cores from 0.01 to nearly 600 metres below the seafloor, in the Western Pacific Region. Applying metagenomics, we identified several taxonomic clusters across all samples, which mainly aligned with depth and sediment type. Inferring functional patterns provided insights into possible ecological roles of the main microbial taxa. These included