A cruise is scheduled for December 5-23, 2013 to visit the Dorado Outcrop, a new Major Program focus site of C-DEBI, with Geoff Wheat from the University of Alaska, Fairbanks as Chief Scientist. I have been given the opportunity to participate aboard this expedition as a shipboard microbiologist. In collaboration with the microbiology team (lead by Dr. B. Orcutt), I will part take in routine microbial and geochemical analyses, which will contribute to the following primary expedition objectives: To determine the ecological and biogeochemical nature of microbial communities in cool crustal fluids from the Dorado Outcrop, and determine the degree to which the communities and chemistry vary by comparison to ridge axis systems; and to determine the influence of cool crustal fluid circulation on sediment and hard-rock microbial ecology and biogeochemistry. These objectives will be further fulfilled post-expedition by various shore-based scientists, using samples that I will help to collect and preserve onboard. As a shipboard scientist, I am also entitled to, and responsible for, contributing to post-expedition research. My specific research plan is to employ single cell genomic techniques to identify the biogeochemical potential of uncultivable heterotrophic organisms present within aerobic marine sediment of the Dorado Outcrop. Revealing the potential functions and life requirements of uncultured organisms will greatly benefit our understanding of elemental cycling in the marine subsurface biosphere.