Researchers have reported the discovery of remnants of seawater dating back to the Ice Age trapped in rock formations in the middle of the Indian Ocean.

Seawater From The Ice Age

Earth was a lot cooler 20,000 years ago. During this period at the tail end of the Ice Age known as the Last Glacial Maximum, sea level was 410 feet lower than it is today and massive glaciers covered much of the continents. Waters were locked up in these glaciers, and the rest were saltier and colder.

Scientists study this period in Earth's history by looking at seafloor sediments and coral fossils, but a better option is now available as researchers discovered an actual sample of seawater from 20,000 years ago.

"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 Clara Blättler, from the University of Chicago. "But from all indications, it looks pretty clear we now have an actual piece of this 20,000-year-old ocean."

Water Squeezed From Underwater Limestone Deposits

Blättler and colleagues made the discovery after collecting sediment core samples from underwater limestone deposits that make up the tiny islands of Maldives in the middle of the Indian Ocean.

The researchers sliced up each of the rock samples and then placed the pieces into a hydraulic press that squeezed water out of the sediments. Preliminary tests of the extracted water showed it was much saltier than normal seawater, indicating that the researchers had something unusual.

Saltier, Colder, And More Chlorinated

The researchers then decided to ran rigorous tests in the lab to examine the chemical elements and isotopes that make up the seawater. The data showed the water was not from today's ocean but from the Last Glacial Maximum, the era when ice sheet sucked up ocean water and the ocean was significantly saltier, colder, and more chlorinated.

"The elevated chloride concentrations and water isotope ratios suggest that seawater from the Last Glacial Maximum is preserved in the subsurface," the researchers wrote in their study. "These pore fluids constrain the properties of an intermediate depth glacial water mass that had higher salinity and δ18O and δD values than the average glacial ocean."

Blättler and colleagues published their findings in Geochimica et Cosmochimica Acta.