Environment Science

20,000-Year-Old Seawater Found Trapped in Limestone from Maldives

Dr Blättler with a vial of 20,000-year-old seawater. Image credit: Jean Lachat

A team of researchers from Princeton University and Universities of Miami and Chicago has found drops of ancient seawater in the sediment cores from the Maldives, a set of small islands in the middle of the Indian Ocean. The seawater could be as old as 20,000 years.

“Previously, all we had to go on to reconstruct seawater from the last Ice Age were indirect clues, like fossil corals and chemical signatures from sediments on the seafloor,” said University of Chicago’s Dr Clara Blättler, lead author of the study.

“But from all indications, it looks pretty clear we now have an actual piece of this 20,000-year-old ocean.”

Dr Blättler and colleagues made the discovery on a months-long mission (Expedition 359 of the International Ocean Discovery Program) exploring the limestone deposits that form the Maldives.

They are actually studying those rocks to determine how sediments are formed in the area, which is influenced by the yearly Asian monsoon cycle.

But when they extracted the water, they noticed their preliminary tests were coming back salt — much saltier than normal seawater.

“That was the first indication we had something unusual on our hands,” Dr Blättler said.

The scientists took the vials of water back to their labs and ran a rigorous battery of tests on the chemical elements and isotopes that made up the seawater.

All of their data pointed to the same thing — the water was not from today’s ocean, but the last remnants of a previous era that had migrated slowly through the rock.

“We are interested in reconstructing the last Ice Age because the patterns that drove its circulation, climate and weather were very different from today’s — and understanding these patterns could shed light on how the planet’s climate will react in the future,” Dr Blättler explained.

“Any model you build of the climate has to be able to accurately predict the past. For example, ocean circulation is a primary player in climate, and scientists have a lot of questions about how that looked during an Ice Age.”

“Since so much fresh water was pulled into glaciers, the oceans would have been significantly saltier — which is what we saw. The properties of the seawater we found in the Maldives suggests that salinity in the Southern Ocean may have been more important in driving circulation than it is today.”

“It’s kind of a nice connection since Cesare Emiliani, who is widely regarded as the father of paleoceanography actually wrote his seminal paper on the subject here at the University of Chicago in 1955.”

“The readings from the water align with predictions based on other evidence — a nice confirmation. The findings may also suggest places to search for other such pockets of ancient water.”

The study will be published in the July 2019 issue of the journal Geochimica et Cosmochimica Acta.

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