My current research interests are marine biogeochemistry and marine microbial ecology with a focus on the deep sub-seafloor biosphere. Through collaborations in the Center for Geomicrobiology I study the processes and microbiology of carbon, sulfur and iron cycling in marine sediments. Important questions include, how do the microorganisms thrive at extremely low energy flux in the subsurface and how do the subsurface microorganisms differ physiologically or genetically from those at the sediment surface? What controls the rates of organic matter mineralization and how do these change with depth and age in the seabed? How important are "cryptic cycles" of sulfur and iron and how do they interact with methane? These questions are studied in sediments from different marine environments with the aim to understand the controls and pathways of the biogeochemical processes and to make geographic extrapolations of their quantitative importance in the seabed.