Jan. 4 (UPI) -- Most of the world's oceans are responding to global warming, but new research suggests there are still pockets of the deep ocean where ancient cooling processes continue to play out.
Scientists at the Woods Hole Oceanographic Institution and Harvard University determined the deep Pacific Ocean is still responding to the 16th century's Little Ice Age.
"Climate varies across all timescales," Peter Huybers, professor of earth and planetary sciences at Harvard, said in a news release. "Some regional warming and cooling patterns, like the Little Ice Age and the Medieval Warm Period, are well known. Our goal was to develop a model of how the interior properties of the ocean respond to changes in surface climate."
The model showed that ancient cooling likely persists in deeply insulated layers of the ocean.
To test the accuracy of their model, which simplifies ocean dynamics, Huybers and his colleagues compared their simulation results with ocean temperature measurements collected by scientific expeditions in the 1870s and 1990s.
Between 1872 and 1876, scientists lowered thermometers deep into the ocean from the three-masted wooden sailing ship HMS Challenger. In the 90s, scientists with the World Ocean Circulation Experiment collected ocean temperature data from across the globe.
"We screened this historical data for outliers and considered a variety of corrections associated with pressure effects on the thermometer and stretching of the hemp rope used for lowering thermometers," said Huybers.
When researchers compared the datasets from the expeditions separated by more than a century, they found surface layers have warmed, as expected, but layers beginning roughly 1.2 miles beneath the surface have cooled.
"The close correspondence between the predictions and observed trends gave us confidence that this is a real phenomenon," said lead study author Jake Gebbie, a physical oceanographer at Woods Hole Oceanographic Institution.
The new findings, detailed in the journal Science, suggest the ocean absorbed as much as 30 percent less heat than previously estimated.