Dynamics of Water Soil Storage in the Unsaturated Zone of a Sand Dune in a Semi-Arid Region Traced by Humidity and Carbon Isotopes: The Case of Ashdod, Israel

• Published in: Radiocarbon
• Main Authors: Carmi, Israel, Stiller, Mariana, Kronfeld, Joel
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 2018
• Subjects: General Earth and Planetary Sciences; Archeology; Carbonic acid
• Online Access: http://dx.doi.org/10.1017/rdc.2018.54; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822218000541

ABSTRACT A 22 m sediment core was collected from the unsaturated zone (USZ) in the dunes south of Ashdod, Israel, in a low rainfall year, following an even lower-rainfall year. The mineralogy of was quartz with some clay and carbonate. The local climate is semi-arid. The roots of the sparse vegetation can reach ~8 m. The porosity was ~40–55%. The DIC ranged from 2 to 13 mmole C/L. Large variability is noted in the soil moisture, with a maximum at the high clay region at ~8 m. Oxygen isotopes enter the USZ with rain falling on the surface. There is 18 O enrichment in the top of the section due to evaporation during the summer. Below this depth δ 18 O values of ~ –5‰ prevail as in the local aquifer. CO 2 and the carbon isotopes enter the USZ laterally by exhalation from roots. The δ 13 C varies from –5‰ to –23‰, representing stages in carbon isotopic fractionation: CO 2gas becomes dissolved CO 2aqueous which then forms carbonic acid and HCO 3 – . The high δ 13 C, Δ 14 C, and DIC are found at the 8 m depth. These values along with high humidity are replicated at ~22m depth. They most probably represent recharge water from the previous rainy season at 8 m depth subsequently pushed down 12.8±0.8 m during the last winter.