Groundwater Age and Rates of Seawater Circulation

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1. Dead Sea aquifer

During her Ph.D. Yael Kiro developed a method to study saline groundwater age and rates of circulation in the aquifer, using Ra isotopes. The concept is based on the fact that the relatively Ra-poor seawater is getting enriched with radium while travelling in the aquifer. The relevant time scales are related to the half life of the isotope in use (in this case, we used  228-Ra, with half life of 6 years, for decade-scales). Since Dead Sea water, unlike the ocean, is very rich with the longer-lived (half life of 1,600 year) 226-Ra, the concentration of this isotope actually decrease while circulating through the aquifer. Therefore, we used the antithetic behavior of 226-Ra and 228-Ra to also determine the extent of Dead Sea water circulation in the aquifer, which is 4-5x106 m3/yr per 1 km of coast. Other aspects of this circulation could be found in Kiro’s papers.

2. Israeli Coastal Aquifers

The age of saline groundwater and rate of circulation in the aquifer were recently studied in the coastal aquifers of Israel using the ratios of the long-lived 226-Ra to shorter-lived isotopes, mainly 223-Ra and 224-Ra. Ratios are expected to be high in relatively ‘old’ water.

In the coastal Pleistocene aquifer, we found no increase in ratios with distance up to 800 m from shore, which suggests ages of no more than a few 100’s years, implying relatively high rates of circulation (i.e. larger than a few m/yr). Currently, we also study the radium parent isotope ratios (e.g. 230-Th/228-Th), as to have better constraints on age calculations.

On the other hand, deep saline water from the Cretaceous aquifer does show high ratios, which suggests they resided in the aquifer for at least 1000’s years.

3. Pore water Ages

under construction