Thirty-eight million years ago, tropical jungles thrived in what are now the cornfields of the American Midwest and furry marsupials wandered temperate forests in what is now the frozen Antarctic.
The temperature differences of that era, known as the late Eocene, between the equator and Antarctica were half what they are today.
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.
New research results published in this week's issue of the journal Science, led by Rensselaer Polytechnic Institute scientist Miriam Katz, are providing some of the strongest evidence to date that the Antarctic Circumpolar Current (ACC) played a key role in the shift.
"What we have found is that the evolution of the Antarctic Circumpolar Current influenced global ocean circulation much earlier than previous studies have shown," said Katz. "This finding is particularly significant because it places the impact of initial shallow ACC circulation in the same interval when the climate began its long-term shift to cooler temperatures."
There has been a debate over the past 40 years on what role the Antarctic Circumpolar Current had in the past cooling trend.
"These climate changes are one of the most significant shifts in Earth's history, from early Cenozoic 'greenhouse' climates to the mid- to late Cenozoic 'icehouse' that saw repeated massive glaciations of the polar regions," said Candace Major, program director in the National Science Foundation's (NSF) Division of Ocean Sciences.
The research was funded by NSF in partnership with the Integrated Ocean Drilling Program, and its predecessor programs, the Ocean Drilling Program and Deep Sea Drilling Project.
"The work by Katz and colleagues is the first to demonstrate that the basic structure of cu
|Contact: Cheryl Dybas|
National Science Foundation