Source of paleo-groundwater in the Emirate of Abu Dhabi, United Arab Emirates: evidence from unusual oxygen and deuterium isotope data

摘要

Paleo-groundwaters of 6000 years BP from the Liwa water-table sand dune aquifer in the Rub al Khali and the Gachsaran artesian carbonate aquifer, on the coast of the Emirate of Abu Dhabi (UAE), exhibit normal δ2H/δ18O slopes, modest δ18O increases, and large negative deuterium excess “d” (Liwa aquifer: 2.19‰ VSMOW and d = –15; Gachsaran aquifer: 3.16‰ VSMOW and d = –28) compared to local Shamal precipitation (0.05‰ VSMOW and d = 7). This unusual isotopic signature is hypothesized to result from re-evaporation of continental runoff to the Red Sea catchment basin. It is postulated that this continental water flowed onto the surface of the Indian Ocean providing a moisture source for the monsoon that dominated precipitation during this, the last wet period in the area from 5000 to 9000 BP. Carbonate precipitation, forming speleothems, travertines, tufas, lacustrine, and capillary-zone deposits, subsequently record this δ18O isotopic signature. This rock record is thus dominated by the water source, rather than environmental conditions of deposition normally assumed to control the rock δ18O isotopic signature. As a consequence, re-evaluation of paleo-climateδ18O data from the rock record may be necessary for this time period in southern Arabia.