The deep marine biosphere hosts a rich microbial community whose dynamics are important analogues to oligotrophic and extra-terrestrial environments, and whose activity bears a major control on the burial of organic carbon and thus global climate. However, these environments are notoriously difficult to study because of their remoteness, limited sampling opportunities and limited material. Numerical models are useful in the context of geochemistry, but many do not explicitly resolve microbes, rather implicitly accounting for microbial processes. Thus, I propose to develop a new biogeochemical-evolutionary model. This research will develop the existing BRNS reaction/transport model and microbial populations will be explicitly resolved (with functionality-based classifications) and will drive geochemical reactions. The evolutionary model will include a trade-off based microbial functionality (similar to the DARWIN model). This research will provide a new tool to the scientific community, and act as a platform for collaboration between experimentalists, modellers, geochemists and microbiologists. Additionally, it will provide quantitate insight into microbial and geochemical coupling in deep marine sediments, with a focus on the Peru Margin, specifically addressing the role of geochemistry in selecting the microbial community, the role of the microbial community in driving geochemical gradients, and the activity of microbes in the sediment profile.