The Deep Oxic Hydrosphere: How Oxygen Persists and Shapes Subsurface Processes
E001
Abstract
Oxygen is essential for life and biogeochemical processes in the Critical Zone, yet its presence in the subsurface is paradoxical. Although aerobic respiration is commonly assumed to deplete O₂ in the unsaturated zone, O₂ persists and reaches remarkably deep groundwater, influencing weathering reactions, microbial activity, and chemical fluxes. This seminar introduces the Deep Oxic Hydrosphere (DOH) concept—a novel framework that highlights how oxygen can traverse and persist in both the unsaturated and saturated zones, with significant implications for subsurface reactivity.
The presentation begins with a reactive transport model that identifies hydrological and geological controls on dissolved O₂ transport to deep aquifers but acknowledges a key gap: the unsaturated zone’s role in sustaining oxygen. An innovative vadose zone monitoring system is then used to explore O₂-powered processes in the deep rhizosphere, demonstrating how aerobic respiration drives solute production through weathering reactions. Seasonal mechanisms regulating O₂ persistence in the VZ, such as liquid-vapor exchanges, and emergent patterns like hysteresis between O₂ and water content, offer new perspectives on oxygen transport and persistence across the VZ to groundwater.
By integrating advanced monitoring techniques and reactive transport modeling, this work redefines the understanding of oxygen’s role in subsurface systems and highlights its implications for subsurface redox dynamics and catchment-scale processes.