Scientists have known for a long time that ocean currents affect climate.  The big unanswered question is how ocean currents change during the periods of greatest change–from ice ages to periods of global warming.

During the Eocene period, 38 million years ago, the Antarctic had a temperate climate.  What is now the midwest United States was covered in tropical jungles.  The temperature differential during that last warm period was much smaller than it is today, when Antarctica is a frozen tundra.

New research suggests that the Antarctic Circumpolar Current (ACC), an ocean current that surrounds Antarctica, played a major role in the Eocene climate shift and that ACC formation played a vital role in the formation of modern ocean structure.  During the Eocene, when temperature differences were not as large between the poles and the midlatitudes, ocean currents were weaker than they are today.  Today, the ACC is considered the most significant ocean current, thermally isolating Antarctica from the rest of the planet, keeping warm surface waters away from the frozen ice sheets.

“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, who is assistant professor of earth and environmental science at Rensselaer.  “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.”

Just how did this shift in ocean currents happen?  That’s not yet understood.

Scientist Miriam Katz points out, “By reconstructing climates of the past, we can provide a science-based means to explore or predict possible system responses to the current climate change.”  As always, science requires more study to start filling in the blanks of the big unknowns!

http://www.sciencedaily.com/releases/2011/05/110526141406.htm