Climatological signals of the paleogroundwater in Jordan

Isotopic data on paleowaters from various groundwater basins in Jordan have been compiled in order to document the various types in terms of age and δ18O–δD relationships. The data indicate that the various types of water can be correlated with the various climatic pluvial phases, which have affected the area since the beginning of the Würm period. Thus the oldest waters (>30 ka) have d values (d=δD−8δ18O) which range from 0.5 to 9; Middle to Late Würm waters from 8.6 to 17; Middle Holocene from 13 to 18; and modern precipitation from 21 to 30. Moreover, the slopes of the regression lines, which describe the various suites of data have been decreasing from 9.3 for the oldest waters; 8.1 for Middle to Late Würm waters; 6.4 for Middle Holocene water and 6.2 for modern precipitation. The trends of the groundwater isotopic contents with time suggest that although pluvials are part of the climatic cycles in the region, there seems to be a significant change in the climatic conditions at the source of the moisture from one pluvial period to the next. This change suggests lower relative humidity over the water masses (i.e. the Mediterranean sea) through time. Moreover, the slopes of the regression lines suggest increasing re-evaporation before recharge through time; also suggesting lower relative humidity in the areas of precipitation. The data suggest that the timing of recharge of waters in the area can be roughly estimated based on the oxygen and deuterium isotopic signature.