What would seem like a barren, inhospitable environment completely devoid of light and low in oxygen is actually flourishing with life. Researchers from the Marine Biological Laboratory (MBL) have, for the first time, described an active microbial community buried deep in cold oceanic crust at North Pond, an isolated sediment pond on the western flank of the Mid-Atlantic Ridge.

Surprisingly, little is actually known about life in the planet's dark, dense, rocky crust, as the only way to get there is by drilling through meters of sediment.

Now, a team led by MBL Associate Scientist Julie Huber has delved into this buried marine biosphere to shed new light on the nature of life way down under.

With seawater running through its rocky crevices, the oceanic crust is anything but static. Researchers say that this natural flow creates a dynamic aquifer through which the ocean's entire volume of water circulates every 200,000 years. 

A subseafloor observatory was installed at North Pond in 2011 as part of the Integrated Ocean Drilling Program. For the recent study, Huber's team examined crustal fluid samples collected in 2012 from 50 to 250 meters beneath the seafloor. 

North Pond
(Photo : MBL)
Map of Mid-Atlantic Ridge and North Pond.

 

The samples collected from North Pond revealed that the microbial community is oxygenated, heterogeneous, and significantly distinct from that found in ocean bottom seawater.

"In many cases, we found the same general group [of bacteria] in the aquifer and in bottom seawater, but different species within that group," Huber explained.

In other words, there were distinct differences in potential microbial activity between the two sites, such as more carbon fixation in the aquifer.

While previous studies have focused on the hot, volcanic fluids at mid-ocean ridges and the subseafloor microbes that survive there, this is the first study to detail the subseafloor microbial community in a cold crustal aquifer site.

"The cold crustal aquifer is a different environment that is also globally important not just in terms of life, but biogeochemical cycling," Huber added. "We are only starting to discover how things proceed there."

Now, researchers are working on a time series to detect if and how the microbial community and fluid chemistry changes in samples collected in 2014. Future surveying is scheduled for 2017.

Their study was published in the March 3 issue of the journal Scientific Reports.