Climate Change: Ancient Warming Interrupted with Significant Cold Snap

Although the Cretaceous, 145 to 66 million years ago, was a period known for its extreme greenhouse climate, a new study shows that this ancient warming was interrupted with a significant cold snap.

This revelation, described in the journal Geology, may help improve prognoses of future climate and environmental development as well as the assessment of human influence on climate change.

During the Cretaceous period, which was one of the warmest times in Earth's history, the poles were devoid of ice and average ocean temperatures in the Atlantic reached up to a sweltering 35 degrees Celsius (95 degrees Fahrenheit).

"A typical greenhouse climate; some even refer to it as a 'super greenhouse,'" Professor Dr. Jens Herrle of the Goethe University and Senckenberg Biodiversity and Climate Research Centre, said in a statement. "We have now found indications in the Arctic that this warm era 112 to 118 million years ago was interrupted for a period of about 6 million years."

This evidence came from samples of the Arctic Fjord Glacier and the Lost Hammer diapir locality on Axel Heiberg Island in Canada. There, they found glendonites, which refer to 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," explained Herrle. "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."

While this is fascinating, does reconstructing the climatic development of the Arctic Ocean during the Cretaceous period, which took place millions of years ago, really help us better understand current climate change? The researchers say, yes.

"The polar regions are particularly sensitive to global climatic fluctuations. Looking into the geological past allows us to gain fundamental knowledge regarding the dynamics of climate change and oceanic circulation under extreme greenhouse conditions. To be capable of better assessing the current human-made climate change, we must, for example, understand what processes in an extreme greenhouse climate contribute significantly to climate change," Herrle said.

In the case of the Cretaceous cold snap, the research team assumes that due to the simultaneous opening of the Atlantic and changes in oceanic circulation and marine productivity, more carbon was incorporated into the sediments. This resulted in a decrease in atmospheric carbon dioxide, which in turn produced global cooling.

Scientists are increasingly trying to gain a better understanding of prehistoric climate change, a goal that just may help us forecast the impacts of future warming.

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