ABSTRACT

Microbial cells occur in shallow and deep sediments throughout the world's oceans. These cells constitute a major portion of the Earth's prokaryotic biomass and their activity catalyzes the decomposition of buried organic matter. Similarly, microorganisms colonize the ocean crust, leading to the oxidative alteration of young ridge flank basalts. Despite their cosmopolitan abundance, the diversity, habitat, and dispersal pathways of these organisms are poorly defined. Little is known regarding their functional genes and the metabolic activities that allow these prokaryotes to grow and survive in the young crustal environment.
North Pond is an isolated northeast-trending sediment pond on the western flank of the Mid-Atlantic Ridge (MAR) at 22deg45'N and 46deg05'W; it is surrounded and underlain by young (7 Ma), porous mid-ocean ridge basalt, and it is isolated from the sediment cover of the Atlantic abyssal basins and outer ridge flanks. This setting provides a "natural laboratory" for examining subsurface microbial community dispersal pathways, occurrence, and colonization patterns. In particular studies can differentiate bacteria and archaea from the deep-sea water column, deep subsurface sediments, and ridge flank basalt. Current deep subsurface microbiology focuses on the question "What kind of microbial life is there, and why?" while avoiding its necessary complement "How did it get there?" This study will accomplish that goal with a vision toward establishing a microbial observatory at North Pond as part of future IODP campaigns. By tracing physical and chemical "signatures" in North Pond sediments, the research will constrain fluid transport pathways and flow rates, and these will be correlated to site-specific microbial composition, key metabolic gene repertoire, and biogeochemical activity of subsurface microbial communities.
This research focuses on detailed mapping of the sediment-basement interface of North Pond, by coupling heat flow, seismic information, and pore fluid chemistry data to microbial sampling of the sediments. The goals are two-fold: 1) to conduct a comprehensive site survey of North Pond that includes constraining the hydrology in preparation for our upcoming IODP cruise to North Pond, and 2) to perform a survey of near-surface microbial communities in conjunction with the biogeochemical characteristics and flow paths of their sediment environment. This site survey cruise will permit necessary refinement in shipboard and shore-based methodology and sample handling in preparation of our IODP cruise.
Broader Impacts. The biogeochemical activities, composition and temporal and spatial dynamics of marine subsurface communities are an emerging central topic in marine sciences and geomicrobiology. The researchers plan to integrate the findings directly into ongoing undergraduate and graduate student education at their institutions through integration of materials in coursework, and the direct involvement of an REU student. The researchers will engage the broader public via the JOI distinguished Speaker series. Finally, this site survey is part of a much larger vision to develop North Pond into an internationally coordinated benchmark study in subsurface microbiology (i.e., a microbial observatory).

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