In the cenotes of the Riviera Maya, the **halocline** is the boundary where fresh water from rainfall and underground aquifers meets the denser salt water that intrudes inland from the ocean. * **Density Gradient:** The halocline exists because the salinity difference prevents immediate mixing. Fresh water (~1.0 g/cm³) floats above salt water (~1.024 g/cm³), creating a distinct interface. * **Optical Effect:** When disturbed by a diver’s movement, the two layers temporarily mix, creating severe