This study explores the genetic and metabolic diversity of microorganisms (Bacteria and Archaea) in a marine oxygen minimum zone (OMZ) off of northern Chile. Microbial metabolism in OMZs contributes to large scale biogeochemical cycles, notably the marine nitrogen cycle. However, the identity of the microorgansims mediating these cycles is largely unexplored. The ecological factors controlling the distribution and activity of OMZ microbes are also largely unknown. Metagenomes generated in this study provide knowledge of the diversity and function of OMZ microbes across depth gradients. Metagenomes were also collected from distinct microbial size fractions, enabling a comparison of free-living and particle-attached microbial communities. This comparison helps identify key functional properties distinguishing microbial life history strategies in the ocean.