Marine sediments contain half of all marine microbial cells, and benthic archaea constitute an important part of those microorganisms. Studies on the activity of these archaea demonstrate these microorganisms are deeply entwined in carbon cycling within sediments and influence the availability of inorganic and organic carbon to the atmosphere and the deep subsurface. However, the metabolic capabilities of most benthic archaea are poorly characterized; therefore, their specific contributions to carbon cycling are unknown. Furthermore, the relationship between genetic and functional diversity of benthic archaeal lineages and the physicochemical and ecosystem controls on that diversity are unknown. This project aims to address these gaps in our knowledge, utilizing stable isotope probing to determine the incorporation of isotopically labelled substrates in conjunction with metagenomic and metatranscriptomic sequencing of benthic archaeal communities within sediments collected across a transect. This approach will identify the autotrophic, heterotrophic, and mixotrophic activity of known and uncharacterized benthic archaea, and assess differences in the magnitude of their activity. Furthermore, the proposed analyses will provide insight on the genetic diversity of expressed genes to help determine what genetic variations determine the archaeal community compositions in different environments and how these organisms relate to those found in the deep subsurface.