May 27, 2011. What a difference 38 million years makes. Back then, the cornfields of the midwestern United States were a tropical region, and the frozen continent of Antarctica was a temperate zone containing forests crawling with marsupial mammals.
According to a new study that has just been released in the journal Science, Significant Role of Oceans in Onset of Ancient Global Cooling, a key mechanism involved in regulating ocean temperatures may be the major factor in the sudden shift from a warm climate to a cool climate that began over 30 million years ago.
“A debate has been ongoing in the scientific community about what changes in our global climate system led to such a major shift from the more tropical, greenhouse climate of the Eocene to modern and much cooler climates.”
According to Miriam Katz, the lead researcher in this study, the Arctic Circumpolar Current (ACC) “played a significant role in this shift.” It had been thought up until now, only deep ocean currents, currents greater in depth than 2000 meters (6000 feet) would only have a significant effect upon ocean temperatures. This study strongly suggests that the ACC mechanism applies to shallow currents, and extends far enough back in time to correlate with the shift toward a cooler climate.
“Katz and colleagues have placed the global impact of the ACC at approximately 30 million years ago, when it was still just a shallow current. Oceans and global temperatures are closely linked. Warmer ocean waters result in warmer air temperatures and vice versa.
In the more tropical environs of the Eocene, ocean circulation was weaker and currents more diffuse. As a result, heat was more evenly distributed around the world. That resulted in fairly mild ocean temperatures worldwide.
Today, ocean temperatures vary considerably and redistribute warm and cold water around the globe.”
Original post: National Science Foundation