Studying ancient bottom rocks of the Pacific Ocean, scientists from Indiana University Bloomington and the Royal Netherlands Institute for Sea Research, concluded that great climate changes occurred during the Mesozoic Era (The Dinosaurs Age), once thought to have been constantly hot and humid.
Ocean surface temperatures varied as much as 6 degrees Celsius (about 11 degrees Fahrenheit) during the Aptian Epoch (in Cretaceous Period) 120 million years ago. "The finding is relevant to the ongoing climate change discussion," IUB geologist Simon Brassell says, "because it portrays an ancient Earth whose temperatures shifted erratically due to changes in carbon cycling and did so without human input."
"Combined with data from the Atlantic, it appears clear that climate changes were taking place on a global scale during this time period," said Brassell, who led the study.
Previous studies from the Atlantic Ocean showed a changeable climate around the same period of time. The researchers were not convinced if the data indicated regional climate change or something on world scale. "We had virtually no data from the middle of the largest ocean at that time period," Brassell said. "The data we collected suggest significant global fluctuations in temperature."
The geoscientists went in 2001 to Shatsky Rise - a research site 1,600 kilometers (1,000 miles) east of Japan and at 3,100 m depth - known to have formed at the end of the Jurassic Period, before to the beginning of the Cretaceous, the last part of the Mesozoic Era. They drilled rocks at 566 m depth.
The early Aptian rock were extremely rich in organic material. By analyzing the carbon and nitrogen content, the geochemists encountered proofs for changes in carbon cycling and in nitrogen fixation by ocean ecosystems associated with the changing climate.
Mean temperature varied between 30 deg C (86 deg F) and 36 deg C (97 deg F) with two prominent cooling episodes of 4 deg C (7 deg F) in tropical surface temperatures during the early Aptian. By comparison, today's tropical sea surface temperatures typically lie between 29 and 30 deg C. "One of the key challenges for us is trying to predict climate change," Brassell said.
"If there are big, inherent fluctuations in the system, as paleoclimate studies are showing, it could make determining Earth's climatic future even harder than it is. We're learning our climate, throughout time, has been a wild beast."