Previous research had placed the development of the deep ACC--greater than 2,000 meters water depth--in the late Oligocene, approximately 23-25 million years ago.
That's well after the global cooling pattern had been established.
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.
"As the global ocean currents were formed and strengthened, the redistribution of heat likely played a significant role in the overall cooling of the Earth," Katz said.
No current is more major than the ACC, scientists believe.
Often referred to as the "mixmaster" of the ocean, the ACC thermally isolates Antarctica by preventing the warm surface waters of subtropical gyres from passing through.
The ACC instead redirects some of that warm water back toward the north Atlantic, creating Antarctic Intermediate Water.
This blocking of heat enabled the formation and preservation of the Antarctic ice sheets, according to Katz.
The circumpolar circulation, Katz concludes, was responsible for the development of the modern four-layer ocean current and heat distribution system.
Katz looked at the uptake of several elements' isotopes, or variants, in the fossil skeletons of small planktonic organisms found in ocean sediments.
Using the dril
|Contact: Cheryl Dybas|
National Science Foundation