Cave atmosphere controls on stalagmite growth rate and palaeoclimate records - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 281

Fig. 1. Schematic illustration of sources (black arrows) and sinks (white arrows) of CO 2 in caves. These vary
considerably in importance from site to site but generally consist of: (a)CO 2 moving as a fluid from the soil zone to
the cave through fissures and secondary permeability. The gas can then either diffuse from the roof downwards or
sink to the floor, depending on the diameter of the fluid column. (b) Degassing from percolation water with a low
percolation rate. This will lead to increased P CO 2 near the roof. (c) Aerobic respiration by biota in the cave. (d) Bacterial
decomposition of organic matter deposited within the cave. (e) Degassing from percolation water with a rapid flow rate.
This will result elevated P CO 2 nearer the floor. (f ) Flow upward into the cave of geothermally-sourced CO 2 .
(g) Degassing from a river or stream. This can also act as a sink, depending on the dissolved P CO 2 of the stream water.
(h) Cave air circulation and ventilation through a connection with the outside atmosphere. This is the most important
sink of cave air CO 2 at most sites.