Dataset: 454 pyrotag sequencing of 16S rRNA genes
Deployment: AT15-35

Twelve igneous minerals and glasses were incubated in 3.5 my old basaltic crust in three flow cells (Smith et al., 2011). Each flow cell was connected to an osmotic pump that ensured continuous fluid flow (~ 30 mL per year) for the duration of the experiment (4 years total). Each flow cell contained four mineral chambers arranged in sequence through which fluid flowed. Each chamber contained only one mineral. In the first flow cell, fluid flowed through chambers containing forsterite, Fo90 olivine, fayalite, and then hornblende. The sequence of minerals in the second flow cell was basalt glass, obsidian, augite, and then diopside. In the third flow cell, fluid flowed from anorthite to bytownite, orthoclase, then apatite (Smith et al., 2011).

Each flow cell-pump assembly was placed into IODP Hole 1301A (47 45.210'N, 127 45.833'W) between 275 and 287 meters below sea floor (Smith et al., 2011). Hole 1301A was emplaced in oceanic crust at 2667 meters below sea level and has a CORK (Fisher et al., 2005) designed to seal the observatory system at the seafloor and allow the aquifer to return to native conditions after drilling and CORK insertion. During the first three years of the incubation, bottom seawater leaked into the observatory and mixed with aquifer fluids, providing a cooler, more oxidant-rich environment for aquifer communities (Wheat et al., 2010). In the fourth year of incubation, seawater entrainment became undetectable and the mineral samples were exposed to fluids characteristic of the natural basement aquifer (Wheat et al., 2010). Minerals were retrieved in August 2008 and frozen at – 40 degrees C until extraction with a FastDNA Spin Kit for Soil.

References:
Smith A, Popa R, Fisk M, Nielsen M, Wheat CG, Jannasch HW, et al. 2011. In situ enrichment of ocean crust microbes on igneous minerals and glasses using an osmotic flow-through device. Geochemistry Geophys Geosystems 12:1–19. doi:10.1029/2010GC003424

Fisher AT, Wheat CG, Becker K, Davis EE, Jannasch H, Schroeder D, et al. 2005. Scientific and technical design and deployment of long-term subseafloor observatories for hydrogeologic and related experiments , IODP Expedition 301 , eastern flank of Juan de Fuca Ridge 1 and general design. Proc Integr Ocean Drill Progr 301. doi:10.2204/iodp.proc.301.103.2005

Wheat CG, Jannasch HW, Fisher AT, Becker K, Sharkey J, Hulme S. 2010. Subseafloor seawater-basalt-microbe reactions: Continuous sampling of borehole fluids in a ridge flank environment. Geochemistry Geophys Geosystems 11:1–18. doi:10.1029/2010GC003057