Geochemical, isotopic, and remote sensing constraints on the origin and evolution of the Rub Al Khali aquifer system, Arabian Peninsula

Abstract

Summary Chemical and stable isotopic compositions of groundwater samples from the Rub Al Khali (RAK) in southern Saudi Arabia were analyzed. Samples were collected from wells of variable depth (1.5–800 m) along the perimeter of the eastern half of the RAK including flowing artesian wells, pumped wells (formerly artesian), and shallow hand-dug wells encompassing those in sabkha areas. Data indicate that the water from the artesian and formerly artesian wells represents the contents of confined aquifers. Such water (Group 1) is isotopically depleted (δ2H values ranging from −60‰ to −35‰), and has total dissolved solids (TDS) concentrations ranging from 1300 to 76,000 mg/L, indicating that much of the salinity is acquired in the subsurface. Water from shallow hand-dug wells including those in sabkha areas (Group 2) has experienced significant evaporation (δ2H values ranging from −34‰ to +19‰) as well as salinization (TDS as high as 92,000 mg/L) by dissolution of sabkha salts including halite and gypsum. Stable isotope data for the Group 2 water samples define an evaporation trend line originating from the Group 1 water samples. This relationship indicates that the Group 2-type water evolved from Group 1-type water by ascending through structural discontinuities, dissolving evaporative salts, and undergoing substantial near-surface evaporation in groundwater discharge zones (sabkhas) characterized by shallow groundwater levels (