As for the geological puzzles, that’s pretty good. In the global greenhouse conditions of the early Eocene (56-48 million years ago), how did a huge number of giant glendonite crystals manage to form?
These rare crystals of calcium carbonate – which require temperatures below 4 degrees Celsius to form – are composed of the mineral ikaite and are found in the tens of millions on the Danish islands of Fur and Mors. They have been dated to 56-54 million years ago.
“Why we find glendonites from a warm period, when temperatures averaged over 35 degrees, has long been a mystery,” says geologist Nicolas Thibault of the University of Copenhagen in Denmark. “It shouldn̵
After a detailed chemical analysis of the glendonite samples by Thibault and an international team of researchers, using a technique called aggregate isotope thermometry to track down temperatures over millions of years, we can have an answer: Maybe the Eocene wasn’t like that evenly warm as previously thought.
The idea of colder Eocene spells has been put forward earlier, but the evidence has so far been inconclusive. The new chemical breakdown helps researchers support the case for colder conditions, with models suggesting that glendonites formed in waters below 5 degrees Celsius (41 degrees Fahrenheit) at a depth of about 300 meters (984 feet).
Sedimentary ash strata on Fur Island indicate the possibility that volcanic eruptions may have been responsible for these colder episodes in the Eocene, localized around specific regions, which would help explain the colder waters and rock record. .
“A large number of volcanic eruptions probably occurred in Greenland, Iceland and Ireland around this time,” says Thibault.
“These droplets of sulfuric acid released into the stratosphere, which could have stayed there for years, shading the planet from the sun and reflecting the sunlight.”
“This helps explain how cold zones were possible at the regional level, which is what influenced the climate in early Eocene Denmark.”
The new study supports the hypothesis that the colder periods of the Eocene are more likely than the alternative, which is that science is wrong about the kind of temperatures at which the ikaite-based rock is capable of forming.
Next, the team wants to see similar investigations carried out to see how widespread the cooling discovered in the Danish basin actually was. Other geological records, including those from the Arctic, suggest that this drop in temperature was not occurring worldwide during the Eocene.
As with any discovery about our climatic past, the study will help scientists map our climatic future.
We may not have the sky cleared by volcanic ash anytime soon, but a rapidly changing climate is something we are going through, just as parts of the world were more than 50 million years ago, long before humans arrived on the scene.
“Our study helps solve a mystery about glendonites, as well as showing that colder episodes are possible during otherwise warmer climates,” says Thibault.
“The same can be said for today, as we are aware of the possibility of sudden climate change.”
The research was published in Nature Communications.