WorldWide Drilling Resource

Looking for Life Deep in the Planet Adapted from Information by the Marine Biological Laboratory One of the more startling discoveries about life on earth in the past 25 years, is that it can - and does - flourish below the ocean floor, in the planet’s dark, dense, rocky crust. The only way to get there is drilling through layers of sediment until rock is reached. Information on this widespread, yet buried marine biosphere is scarce. A team led by Marine Biological Laboratory Associate Scientist Julie Huber added new details to our understanding of life way below the surface. She and her colleagues offered the first description of an active microbial community buried in cold oceanic crust at North Pond, an isolated sediment pond on the western flank of the Mid-Atlantic Ridge. The oceanic crust is a hotbed of activity. Seawater runs through its rocky crevices, creating a dynamic aquifer through which the entire volume of the ocean circulates every 200,000 years. Huber’s team discovered the microbial community in North Pond crustal sam- ples was oxygenated, heterogeneous, and noticeably distinct from the commu- nity found in seawater at the bottom of the ocean. “In many cases, we found the same general group [of bacteria] in the crustal aquifer and bottom seawater, but different species within that group,” said Huber. This indicates distinct differences in po- tential microbial activity between the two sites, such as more carbon fixation in the aquifer. A paper by Huber and fellow re- searchers will be the first to describe the subseafloor microbial community in a cold crustal aquifer site. Prior work fo- cused on the hot, volcanic fluids at mid- ocean ranges and the subseaf loor microbes surviving there. “The cold crustal aquifer is a different environment that is also globally important, not just in terms of life, but biogeochemical cycling,” noted Huber. “We are only starting to discover how things proceed there.” Samples were obtained from a sub- seafloor observatory installed at North Pond by the Integrated Ocean Drilling Program in 2011. Combining genomic technologies with geotechnical meas- urements, Huber’s team examined crustal fluid samples retrieved in 2012 from 164-820 feet beneath the seafloor, under more than 2 miles of seawater. The re- searchers are working on a time series to detect if and how the microbial com- munity and fluid chemistry changes. Currently, 2014 samples are being ana- lyzed, and more samples will be col- lected this year. The oceanic crust at North Pond is relatively young at 8 million years old; and its circulating fluids are cold in comparison to other crustal fluids. 10 JANUARY 2017 WorldWide Drilling Resource ®