"Most people think the mid-Cretaceous period was a super-greenhouse," says Darren Gröcke, assistant professor and Director of the Stable Isotope Biogeochemistry Laboratory at McMaster University. "But in fact it was not to dissimilar to the climates over the past 5 million years."
By using high-resolution stable-isotope analysis from 95-million-year-old fossilized wood collected from Nebraska, Gröcke and his team were able to precisely correlate the terrestrial carbon cycle with that from deep-sea records. However, when they compared the carbon curves from both records, it was evident that a chunk of about 500,000 years was missing from the terrestrial record. Other records already indicated a drop in sea level, a 2-4ºC drop in oceanic temperature and a breakdown in oceanic stratification coincident with a marine extinction event.
"Rapid, large falls in sea-level in the ancient record are typically only produced by a glaciation, and so the combination of all the data during the mid-Cretaceous period suggests a short-lived glaciation during a period generally considered to be a super-greenhouse," says Gröcke.
"Whatever hits the water causes a ripple effect on land," says Gröcke. "Earth often undergoes rapid temperature fluctuations, and this new information may help us to understand how the biosphere will respond to human-generated alterations of CO2 concentration."
He said the research not only challenges conventional wisdom surrounding ancient climates, it makes a case for the use of high-resolution sampling in order to reconstruct a more accurate picture of the ancient climate and its affect on the Earth.
Funding for this study was provided in part by the Natural Science and Engineering Research Council of Canada, Canada Foundation for Innovation, and the Ontario Innovation Trust.