To examine microbe-mineral interactions in subsurface oceanic crust, we evaluated microbial colonization on crustal minerals that were incubated in borehole fluids for 1 year at the seafloor wellhead of a crustal borehole observatory (IODP Hole U1301A, Juan de Fuca Ridge flank) as compared to an experiment that was not exposed to subsurface crustal fluids (at nearby IODP Hole U1301B). In comparison to previous studies at these same sites, this approach allowed assessment of the effects of temperature, fluid chemistry, and/or mineralogy on colonization patterns of different mineral substrates, and an opportunity to verify the approach of deploying colonization experiments at an observatory wellhead at the seafloor instead of within the borehole. The Hole U1301B deployment did not have biofilm growth, based on microscopy and DNA extraction, thereby confirming the integrity of the colonization design against bottom seawater intrusion. In contrast, the Hole U1301A deployment supported biofilms dominated by Epsilonproteobacteria (43.5% of 370 16S rRNA gene clone sequences) and Gammaproteobacteria (29.3%). Sequence analysis revealed overlap in microbial communities between different minerals incubated at the Hole U1301A wellhead, indicating that mineralogy did not separate biofilm structure within the 1-year colonization experiment. Differences in the Hole U1301A wellhead biofilm community composition relative to previous studies from within the borehole using similar mineral substrates suggest that temperature and the diffusion of dissolved oxygen through plastic components influenced the mineral colonization experiments positioned at the wellhead. This highlights the capacity of low abundance crustal fluid taxa to rapidly establish communities on diverse mineral substrates under changing environmental conditions such as from temperature and oxygen.
Two years ago, we reported to Current readers about a novel ship-to-shore education and outreach program called the “Adopt-A-Microbe” (AAM) project (Orcutt et al. 2011). AAM focused on raising awareness of microscopic life—“microbes”—living in the deep marine subsurface to middle school audiences while engaging them in the science of the ocean-drilling program, both fundamental components of the Center for Dark Energy Biosphere Investigations (C-DEBI) mission. The AAM project was originally designed as an interactive set of web-based activities to be done in real-time in coordination with a research expedition, involving on-going interactions with scientists at sea.
The East Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) comprise a ridge segment in the southwest Pacific Ocean where rapid transitions in the underlying mantle chemistry manifest themselves as gradients in seafloor rock geochemistry. We studied the geology and microbial diversity of three silicate rock samples and three inactive sulfide chimney samples collected, from north to south, at the vent fields Kilo Moana, ABE, Tui Malila, and Mariner. This is the first study of microbial populations on basaltic andesite, which was sampled at Mariner vent field. Silicate rock geochemistry exhibits clear latitudinal trends that are mirrored by changes in bacterial community composition. α-proteobacteria, ε-proteobacteria, and Bacteroidetes are most common on a silicate collected from Kilo Moana and their proportions decrease linearly on silicates collected further south. Conversely, a silicate from Mariner vent field hosts high proportions of a unique lineage of Chloroflexi unrelated (<90% sequence similarity) to previously recovered environmental clones or isolates, which decrease at ABE and are absent at Kilo Moana. The exteriors of inactive sulfide structures are dominated by lineages of sulfur oxidizing α-proteobacteria, γ-proteobacteria, and ε-proteobacteria, while the interior of one chimney is dominated by putative sulfur-reducing δ-proteobacteria. A comparison of bacterial communities on inactive sulfides from this and previous studies reveals the presence of a clade of uncultured Bacteroidetes exclusive to sulfidic environments, and a high degree of heterogeneity in bacterial community composition from one sulfide structure to another. In light of the heterogeneous nature of bacterial communities observed here and in previous studies of both active and inactive hydrothermal sulfide structures, the presence of numerous niches may be detected on these structures in the future by finer scale sampling and analysis.
During Integrated Ocean Drilling Program (IODP) Expedition 336 to North Pond on the western flank of the Mid-Atlantic Ridge (8 Ma crust) in the late fall of 2011, borehole observatories were installed in IODP Holes U1382A and U1383C and Deep Sea Drilling Project Hole 395A. These borehole observatories are designed for long-term (multiyear) coordinated hydrogeological, geochemical, and microbiological monitoring and experimentation to understand the nature of life, fluid flow, and fluid-rock interactions in young and cool oceanic crust. Additional related activities during Expedition 336 included recovery of an instrument string that was deployed within an earlier generation of a circulation obviation retrofit kit (CORK) observatory in Hole 395A and preparation of IODP Hole U1383B, which was drilled, cased, and left open during Expedition 336, for a future deployment of a borehole observatory. A streamlined CORK observatory was deployed in Hole U1383B during a remotely operated vehicle–supported cruise in April 2012. An additional CORK servicing cruise is scheduled for 2013. Here, we summarize the observatory project goals and provide an overview of the design, construction, and deployment of these CORKs and related instrumentation during Expedition 336. We also summarize the project goals, design, and construction for the CORK-lite installation in Hole U1383B and discuss plans for its deployment. CORK servicing plans for 2012 and 2013 also are presented.
Integrated Ocean Drilling Program (IODP) Expedition 327 installed two new subseafloor borehole observatory systems (“CORKs”) in 3.5 m.y. old upper ocean crust on the eastern flank of Juan de Fuca Ridge in Holes U1362A and U1362B. Expedition 327 participants also recovered part of an instrument string previously deployed in a CORK in Hole U1301B and deployed a short replacement string. These observatories are part of a network of six CORKs that was designed to monitor, sample, and complete multidisciplinary cross-hole experiments. We present an overview of project goals and describe the design, construction, and deployment of new CORK systems. We also provide an update on the status of preexisting CORK systems as of the start of Expedition 327. Additional CORK servicing and sampling are scheduled for summer 2011 and 2012, including a long-term free-flow perturbation experiment that will test the large-scale directional properties of the upper ocean crust around the observatories.