In the context of Mediterranean coastal karst aquifers, characterized by a double-flow (even triple) model, their dynamic nature renders them highly responsive to chemical variations and groundwater level fluctuations. This sensitivity is particularly pronounced in coastal regions where aquifers exhibit an extensive subsurface conduit network linked to the rock matrix, facilitating groundwater discharge to the sea. Consequently, these aquifers are susceptible to seawater intrusion, with rapid responses to rainfall and pumping, making them highly sensitive to short-term weather variations and long-term climate change. Focusing on Mallorca Island in the western Mediterranean Sea, our study aimed to analyze the environmental implications of global and climate change on seawater intrusion in Mediterranean coastal karst aquifers. Employing various methodologies, including hydrochemical techniques and multi-isotopic analysis, we investigated isotopes such as 2H and 18O in water molecules, 87Sr/86Sr ratio, δ11B in water, δ15N and δ18O of nitrate in groundwater, and δ34S and δ18O of sulfate. Our most significant results include the following: 1. Nitrate in groundwater or Freshwater-Seawater Interface originates from agricultural sources. 2. Sulfate isotopic composition indicates hydraulic connections in the lower hydrogeological complex of the Serres de Llevant. 3. Partial mixing of freshwater with brackish water near the freshwater-seawater interface or saltwater domes can lead to significant problems, contributing to soil sodification. 4. The rebound effect, characterized by aquifer recontamination due to molecular back-diffusion after the cessation of extractions and marine intrusion retreat, provides insights into the impact of climate and global change on karst aquifers.