Final answer:
Carbonation is the process that can occur far below the surface in the tropics, where limestone dissolves in acidic solutions formed by groundwater and atmospheric CO2, leading to cave formation and features like stalactites and stalagmites.
Step-by-step explanation:
Among the options given, the phenomenon that can occur far below the surface in the tropics is carbonation. This process involves the dissolution of limestone (CaCO3) through a reaction with groundwater containing atmospheric CO2, forming a weakly acidic solution. Over time, this can lead to the creation of caves with the formation of stalactites and stalagmites as CaCO3 precipitates out of the solution. The chemistry of cave formation is a clear demonstration of carbonation occurring deep beneath the Earth's surface, with the added complexity of shifts in pH-dependent solubility equilibriums, influenced by factors such as the escape of carbon dioxide and evaporation of water.