I'm not familiar with Mallorca's hydrogeology, but I've done some cenote (cavern) diving in Mexico's Yucatan peninsula. The caves are inland, but sea water infiltrates through the porous and channel-filled rock. The water nearer the surface is rainwater.
The narrow region where freshwater and seawater intermingle is called the halocline, it creates a cool optical distortion which reminds me of the "oil paint" filter in photoshop.
The narrow region where freshwater and seawater intermingle is called the halocline, it creates a cool optical distortion which reminds me of the "oil paint" filter in photoshop.