These direct remnants were found in pockets of seawater that are tucked inside rock formations at the heart of the Indian Ocean, which could reveal crucial information about how the ocean reacted to the geophysical changes of the last Ice Age. In turn, this knowledge could contribute towards improved climate models to help understand the climate changes we currently face.
“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 Blättler, assistant professor of geophysical sciences at 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.”
Blättler and her team made the discovery on a month-long scientific expedition to the Maldives. The focus of the study was on the limestone deposits that form the islands and they were trying to determine how sediments are formed in that area.
“That was the first indication we had something unusual on our hands,” Blättler said. They noticed that the initial samples from their water extractions were far saltier than normal seawater, so they ran a vast array of tests on the chemical elements and isotopes that made up the seawater. They concluded that these samples of water had migrated slowly through the rock, remnants of a previous era.
“Since so much fresh water was pulled into glaciers, the oceans would have been significantly saltier—which is what we saw,” Blättler added. “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.”
More information on the study will be published in volume 257 of the Geochimica et Cosmochimica Acta in July 2019.
Photograph by Jean Lachat, courtesy of The University of Chicago via Facebook.
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