June 18, 2014
Dr. Jason Sylvan, University of Southern California
Microbial life in old subseafloor basaltic crust
The aquifer in subseafloor basaltic crust is a massive, continuous microbial substrate, yet sparingly little is known about life in this habitat. The work to date has focused largely on young crust at oceanic spreading regions and ridge flanks, where the basaltic crust is still porous and fluid flow through it is active. Heat flow models predict that little fluid moves through subseafloor basalt >65 million years old, but recent work proves that seamounts, which are found throughout the seafloor, act as mid-plate conduits into and exits out of the subsurface aquifer for fluids and possibly microbes. To determine if life does indeed exist in old subseafloor basaltic crust, I sampled 64-74 million year old extinct seamounts along the Louisville Seamount Chain in the southwest Pacific Ocean during Integrated Ocean Drilling Program Expedition 330. Newly developed methods for quantifying subsurface microbes were applied to these samples, providing the first quantification of microbes in cores retrieved from subseafloor basaltic crust. Analysis of community DNA indicated archaea are extremely rare in this setting. The most abundant bacterial classes detected were Actinobacteria, Flavobacteria, Sphingobacteria, Bacilli, Clostridia, Alpha-, Beta and Gammaproteobacteria. Genera putatively carrying out hydrocarbon oxidation and nitrogen, sulfur and metal redox processes were commonly detected in core samples as well as enrichment incubations started during the cruise. This work shows that old subseafloor basalt is indeed home to microbial communities that may have a significant impact on marine biogeochemistry. I will discuss these results in more detail and put them in context with previous studies of microbiology in subseafloor basaltic crust.
Jason received his BS in Biology from Brandeis University in 1999, with minors in Environmental Science and Music. In graduate school, he studied marine biogeochemistry and eutrophication under Jim Ammerman, receiving his MS in 2004 and his PhD in 2008, both in Biological Oceanography, from Rutgers University in New Brunswick, NJ. Jason moved to Los Angeles in 2008 and began a postdoc studying deep sea geomicrobiology in the lab of Katrina Edwards at University of Southern California. In February 2013, he was appointed as a Research Assistant Professor in the Department of Biological Sciences at USC.