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Rains, steam, and everything in between

A comparison between the level of evaporation in the current Dead Sea compared to the ancient period, may help in understanding the climate that existed in our region, in the past

Evaporation of the Dead Sea. Illustration: depositphotos.com
Evaporation of the Dead Sea. Illustration: depositphotos.com

Geochemistry ("chemistry of the earth") is a branch that studies the distribution of chemical elements and natural compounds and uses chemical methods to learn about geological, biological and climatic systems and processes that have occurred and are occurring on Earth.

Prof. Hagit Afek from the Institute of Earth Sciences at the Hebrew University of Jerusalem, is an environmental geochemist whose research focuses on reconstructing the Earth's climate based on isotopes - atoms of chemical elements that differ from each other in the number of neutrons and mass. For example, carbon 12 which is the lighter and more common and carbon 13 which is the heavier and rarer.

What is the question? What is the amount of evaporation that took place in the last 70,000 years in the Dead Sea?

Calcium carbonate deposits formed in the ancient Dead Sea, in the area of ​​Masada
Calcium carbonate deposits formed in the ancient Dead Sea, in the area of ​​Masada

"Understanding the past climate, thousands to millions of years ago, helps us to better predict the future climate. Current climate change is man-made, but the physics of the climate system has not changed and if we understand how it has responded to past changes, we can predict how it will respond in the future. For example, even in the past there were periods when the level of carbon dioxide in the atmosphere was high and led to warming," explains Prof. Afek.

To decipher the past temperature and the water cycle on Earth, the researcher developed two methods - "conjugated isotopes" and "oxygen 17". Conjugated isotopes are the chemical bonds between two heavy isotopes, for example between carbon 13 and oxygen 18, and the researcher examines them in the mineral calcium carbonate (calcium carbonate) which exists, for example, in sedimentary rocks and oysters. This is how she deciphers the temperature at which the mineral was formed. According to her, "I measured the amount of conjugated isotopes in samples such as fossilized oysters that are 50-40 million years old, from the Eocene period, originating from the Antarctic Peninsula (which is very sensitive to climate change). If the fossils contain chemical bonds that include few conjugated isotopes - this means that they were formed at a high temperature, and vice versa. This is how we discovered that these oysters were formed at a temperature of about 15 degrees, much higher than today in this area. We know that during this period it was generally warm and the concentration of carbon dioxide was high." Calcium carbonate deposits formed in the ancient Dead Sea, in the area of ​​Masada

Oxygen 17 is a rare isotope, one of the three isotopes of oxygen - 16, 17, 18. By measuring it in water and calcium carbonate, it is possible to obtain hydrological information that complements the information obtained from conjugated isotopes regarding the climate. "Measuring oxygen 17 in calcium carbonate (which comes, for example, from the sediments of the ancient Dead Sea and decanters in caves) can give us information about the sources of the rain (where it came from) and the conditions of its formation and the level of water evaporation in the lake. That is, calcium carbonate preserves the composition of the water in which it is formed, therefore it is possible to measure the level of oxygen 17 in it and obtain information about the level of evaporation in the lake and changes in the rainfall regime over hundreds to thousands of years," explains Prof. Afek.

In their current research, which was awarded a grant from the National Science Foundation, Prof. Afek and her team are trying to reconstruct the level of evaporation in the Dead Sea (which, among other things, leads to its drop) and to understand how it has changed over the past 70,000 years, and what it means for the climate in the region. "The purpose of the research is to examine the evaporation in the current and ancient Dead Sea in order to understand the past climate in our region through it. Understanding evaporation will make it possible to quantify the water balance in the lake to see if changes in its level are due to a decrease or increase in the level of evaporation or the amount of rain," says Prof. Afek.

To test this, the researchers measure the level of oxygen 17 in samples of the Dead Sea water and the calcium carbonate formed in it using a mass spectrometer. According to Prof. Afek, "The more evaporation there is, the water that remains in the lake contains more oxygen 17 and 18 (the heavy isotopes) and the water that evaporates contains more oxygen 16 (the light isotope). We measure the concentrations of 17 and 18, and the ratio between them depends on the humidity conditions at the time of evaporation. A low ratio indicates increased evaporation. This way we can understand how much evaporation occurred over the years in the ancient and modern Dead Sea and at what humidity."

We found that there were periods when the humidity level was low and evaporation increased and periods when the opposite happened. But the research is still in its early stages, so it is too early to draw far-reaching conclusions.

So far, preliminary data on the ancient Dead Sea have been obtained: large differences have been found over the years in the level of humidity and evaporation. "We discovered that there were periods when the humidity level was low and evaporation increased and periods when the opposite happened. But the research is still in its early stages, so it is too early to draw far-reaching conclusions. In the end, the intention is to restore the water balance in our region and to understand how it changed over time and affected the climate of the past", concludes Prof. Afek.

Life itself:

Prof. Hagit Afek, 52, mother of 10. Eight years ago she returned to Israel from the USA (where she worked as a professor in the Department of Geology and Geophysics at Yale University) and since then has lived in Jerusalem. In her free time she is engaged in gardening.

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