Ventilation of a Single-Entrance Cave by Buoyancy-Driven Exchange Flow

Abstract Karst caves are unique subsurface environments in which climate is governed by the interplay between advective heat transport by airflow, convective heat exchange at the rock–air interface, and conductive heat transport within the surrounding rock. Airflow is a major driver of heat and CO₂ exchange between the cave environment and the atmosphere, yet the physical mechanisms controlling cave ventilation across different morphologies and timescales remain poorly understood. We investigate temperature and airflow in a single-entrance cave consisting of a dominant down-sloping passage connected to a set of chambers. Such caves exhibit buoyancy-driven ventilation during cold periods, when dense external air descends along the floor of the entrance passage while warmer cave air ascends along the ceiling as a bidirectional counterflow. During warm periods, ventilation is largely suppressed and cave temperatures gradually equilibrate. Airflow and temperature observations reveal a buoyancy-driven exchange flow governed by heat transfer with the surrounding rock and sediments and mixing between the opposing layers. Cooling of the rock and sediments during cold-air intrusions prolongs ventilation and modifies the response to subsequent cooling events. Thus, ventilation depends on both the instantaneous cave–atmosphere temperature difference and the thermal history of the surrounding rock and sediments.