Colonization of subsurface microbial observatories deployed in young ocean crust

Area of Science:

• * Marine biology
• * Geomicrobiology
• * Subseafloor ecosystems

Background:

• * Oceanic crust is Earth's largest hydrogeologic reservoir, with poorly understood microbial ecosystems.
• * Subsurface biosphere research is limited by compromised samples from traditional ocean drilling.
• * In situ experiments offer a novel approach to studying life in this extreme environment.

Purpose of the Study:

• * To investigate the dynamic response of subseafloor microbial ecosystems to changing conditions.
• * To characterize microbial life in young basaltic oceanic crust using long-term observatories.
• * To understand the functioning of the largest, yet least understood, biotope on Earth.

Main Methods:

• * Deployment of in situ experimental observatory systems in young basaltic crust (3.5 Ma) on the eastern flank of the Juan de Fuca Ridge.
• * Long-term monitoring (4 years) of microbial colonization and community shifts under varying physical and chemical conditions.
• * Analysis of biosignatures (e.g., iron oxyhydroxide stalks) and microbial community structure (bacterial and archaeal).

Main Results:

• * Initial colonization by iron-oxidizing bacteria indicated by biogenic iron oxyhydroxide stalks under cool, oxic, iron-rich conditions.
• * Microbial community structure shifted to reflect natural conditions (warmer, reducing) after thermal and chemical recovery.
• * Firmicutes dominated the post-rebound bacterial community; archaeal diversity remained extremely low.

Conclusions:

• * In situ observatory experiments provide crucial insights into natural hydrological systems and subseafloor biospheres.
• * Microbial ecosystems in oceanic crust are dynamic and respond to environmental changes over time.
• * This study advances our understanding of the vast and understudied subsurface basaltic biosphere.