A better understanding of organic hydroperoxides
17 March 2023
Published online 20 April 2017
Dead Sea drill cores reveal worrying insights into ancient climate.
Around 120,000 years ago, when the average temperature on Earth was only slightly warmer than present, the Dead Sea shrunk to 20% or less than its current volume –– indicative of a devastating regional drought.
Rainfall changes around the Dead Sea, which is fed by the Jordan River with its headwaters in Syria and Lebanon, reflect the climate in most of the Levant.
In 2010 the Dead Sea Deep Drilling Project (DSDDP) drilled a core almost half a kilometer below the floor of the middle of the Dead Sea.
According to Steven Goldstein, a geochemist at Columbia University’s Lamont-Doherty Earth Observatory, the DSDDP core reveals 200,000 years of climate history, showing the ebb and flow of the lake during cold glacials and warm interglacials in sequence. An inter-disciplinary team of scientists, mainly based at Lamont-Doherty Earth Observatory and have recently analyzed the DSDDP core, changing the way we understand the past and better predict future climatic events in the region.
Thick levels of salt deposits suggest prolonged drought, as Goldstein explains, “when evaporation is greater than the amount of water that’s coming in, the water evaporates and reaches the point where it can’t hold the salt any more and so salt is deposited.” Tiny bubbles formed within the salts, which “are like time capsules that trap the lake water at the time, so we know the composition of the lake at a given time, says Yael Kiro, also a geochemist at Lamont-Doherty Earth Observatory.
The most acute drought began 120,000 years ago and lasted 15,000 to 20,000 years.
Kiro and the team — for the first time — have been able to quantify changes in the salt deposits, allowing estimates of the available amount of fresh water in the Dead Sea watershed. They used liquid nitrogen to freeze the water trapped in the salt crystals and analyzed its chemical composition, according to Kiro.
The analysis has identified two intervals of extreme drought. The most recent dry period was around 10,000 years ago, during the Holocene — our current epoch — when temperatures were similar to present day.
The most acute drought began around 120,000 years ago and lasted 15,000 to 20,000 years, during which the average amount of water in the Dead Sea was down 50% to 20% of the present day, Kiro reports.
During the most extreme dry periods, 80% of the water needed by people in the area would not be available, says Goldstein.
The amount of rainfall in the area and the volume of water in the Dead Sea are not, “a 1 to 1 thing, but we’ve estimated the amount total precipitation would be down something between 40 – 60%” in the headwaters, adds Goldstein.
Such a drought would have a huge impact on the amount of water available in Lebanon, Jordan, Syria, Palestine, and Israel.
Predictions of rainfall and climate are made in part by models that estimate climate change in the present, and which describe past climates — or what scientists refer to as paleoclimates.
The climate models accuracy, however, can be checked by testing them against the paleoclimate data from the DSDDP core, explains Yochanan Kushnir, an ocean and climate physics research professor at the Lamont-Doherty Earth Observatory.
The periods of extreme drought in the climate models correspond with the salt layers in the drill cores, as Kushnir reports, “We are very encouraged that the models seem to agree with what we are finding, meaning that they are not far away from the truth when we extrapolate towards the future.”
Kushnir cautions that the team still needs to better understand why the region’s paleoclimate was so much drier than the present. Yet, the first results provide fascinating insights into the past climate and provide grave warnings for the future.
“If we can instill confidence in predictions by looking at the past,” explains Kushnir, “then hopefully people will take it more seriously in terms of planning for the future.”