Extreme Global Warming of the Cretaceous Marked by Surprising Cooling Period

Scientists have learned a bit more about the climate of the Arctic Ocean during the Cretaceous period. Recreating the past climatic development, they found that the region suffered a severe cold snap during the age that was known for its extreme greenhouse climate.

The Cretaceous period occurred about 145 to 66 million years ago and was one of the warmest periods in the history of Earth. At the time, the poles were devoid of ice and average temperatures of up to 35 degrees prevailed in the oceans.

In order to learn a bit more about past climate, the researchers sampled the Arctic Fjord Glacier and the Lost Hammer diaper locality on Axel Heiberg Island in intervals. This allowed them to find glendonites, which are star-shaped calcite minerals that have taken on the crystal shape of the mineral ikaite.

"These so-called pseudomorphs from calcite to ikaite are formed because ikaite is stable only below 8 degrees Celsius and metamorphoses into calcite at warmer temperatures," said Jens Herrle, one of the researchers, in a news release. "Thus, our sedimentological analyses and age dating provide a concrete indication for the environmental conditions in the cretaceous Arctic and substantiate the assumption that there was an extended interruption of the interglacial period in the Arctic Ocean at that time."

By looking at the geologic past the researchers don't only learn a bit more about the Cretaceous. They also learn a bit more about climate in general under extreme greenhouse conditions. This, in turn, may have implications for the warming climate of today.

In the case of the Cretaceous cold snap, the opening of the Atlantic in conjunction with changes in oceanic circulation and marine productivity caused more carbon to be incorporated into marine sediments. This resulted in a decrease in the carbon dioxide content of the atmosphere, which then produced global cooling.

The findings revealed a bit more about the past era. This, in turn, may have implications for current climate change.

The findings are published in the journal Geology.

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