Project: Buried alive: Microbial responses to sediment flux with implications for the deep biosphere

Previous investigation of the microbial diversity of unconsolidated marine sediments has not yet constrained the importance of cell transport associated with physical processes of sedimentation and fluid advection. Organisms must migrate in order to maintain position with respect to geochemical gradients, and many marine bacteria exhibit chemotactic behavior to optimize their position. However, certain microorganisms in subsurface environments form persistent attachments to solid particles or are non-motile, leading to the differential burial of a subset of active cells (i.e. what is preserved may differ from what is—or was—active at a given horizon). Deep sedimentary horizons may inherit a microbial community that fails to maintain its optimum position with respect to geochemical profiles, and the deep biosphere ultimately is composed of cells that survive this transition.

We seek to describe the permanence and overprinting of molecular signatures of microbial communities across discrete horizons associated with rapid sedimentation (e.g. turbidite emplacement), changes in bottom-water geochemistry, and depositional unconformities. This work involved the collection and study of sediment cores from 3 lakes in the Minneapolis-St. Paul Metropolitan, an intact turbidite profile from La Jolla Canyon on the California Borderland, and select core samples from a marine transgressive sequence drilled by IODP leg 337 off the Shimokita Peninsula, Japan. These core samples provided a key opportunity to study microbial relationships to sedimentology at high resolution. Preliminary work suggests microbial community signatures retain evidence of cell displacement resulting from sediment disturbance, and distinct patterns in diversity are not overprinted on decadal timescales.  

This work was supported through a C-DEBI postdoctoral fellowship.