Fluids from the Oceanic Crust Support Microbial Activities within the Deep Biosphere

Abstract

The importance of crustal fluid chemical composition in driving the marine deep subseafloor biosphere was examined in northeast Pacific ridge-flank sediments. At IODP Site U1301, sulfate from crustal fluids diffuses into overlying sediments, forming a transition zone where sulfate meets in situ-produced methane. Enhanced cell counts and metabolic activity suggest that sulfate stimulates microbial respiration, specifically anaerobic methane oxidation coupled to sulfate reduction. Cell counts and activity are also elevated in basement-near layers. Owing to the worldwide expansion of the crustal aquifer, we postulate that crustal fluids may fuel the marine deep subseafloor biosphere on a global scale.

Keywords:

• Integrated Ocean Drilling Program
• JOIDES Resolution
• Expedition 301
• deep biosphere
• subsurface microbiology
• oceanic crust
• Juan de Fuca hydrogeology
• hydrothermal fluids
• microbial activity
• AOM
• sulfate reduction
• methanogenesis
• rates
• MPN
• exoenzymes

ACKNOWLEDGMENTS

We thank the crew, the shipboard scientific party of IODP Exp. 301 and the chief scientists for valuable support during the cruise. Special thanks go to Helge Nieman for his help with the AOM data analysis. This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). Funding for this research was provided by a grant of the German Research Foundation (DFG).

Authors Engelen and Ziegelmüller contributed equally to this work.