The Negev desert, which covers half of Israel’s land mass, is so dry that parts of it get less than three inches of water a year. But beneath it is water that sustains the people and agriculture of the region. Understanding where it came from, how much is there and what’s happening to it is critical to the security and allocation of that crucial resource.

Researchers at Ben-Gurion University of the Negev in Israel are collaborating with colleagues at the University of Chicago and affiliated Argonne National Laboratory to better understand the Nubian Sandstone Aquifer system, which lies beneath a large portion of the Negev and other parts of Israel.

By combining Argonne’s pioneering radiokrypton dating technique with other isotopic signatures of the water’s composition, the researchers are not only able to tell when that water was deposited, but where it came from and the climate conditions that produced it up to nearly 400,000 years ago. The result, detailed in a new study in the Proceedings of the National Academy of Sciences, marks the first time that scientists have been able to use groundwater to build a picture of the water of ancient climates dating back that far.

“Clean water is vital for sustaining life, and we need to be able to predict future water availability as global warming advances—which depends on understanding water distribution during past warmer and colder periods,” said Reika Yokochi, research associate professor in the Department of Geophysical Sciences at the University of Chicago and the first author of the study. “This project shows us these tools could be really transformative—tracing water movement much further than we’ve previously been able to.”

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Photo by Roland Purtschert