Why does calcium carbonate come out of solution when water enters a cave?

When water enters a cave, calcium carbonate (often in the form of calcite) comes out of solution primarily because of the loss of carbon dioxide.123

As rainwater infiltrates the soil, it absorbs carbon dioxide to form a dilute solution of carbonic acid. This acidic water dissolves calcium carbonate from the limestone bedrock as it travels downward. When this mineral-rich water eventually emerges from the ceiling or walls into the cave atmosphere, the partial pressure of carbon dioxide in the cave air is typically lower than that in the water.243

Consequently, carbon dioxide escapes from the water into the cave atmosphere. This loss of carbon dioxide reduces the water's ability to hold calcium carbonate in solution, forcing the mineral to precipitate and form speleothems such as stalactites, stalagmites, and flowstone. In some cases, evaporation can also contribute to the deposition of minerals, particularly with more soluble substances like gypsum.123