At the end of the last Ice Age, the Northern and Southern hemispheres both underwent a series of climate changes that eventually led to deglaciation. This much is known. But researchers have long wondered about the extent to which one hemisphere's climate activity influenced the other. Scientists have put forth three models: one holds that northern ice sheets drove climate shifts in the south; another posits that the two changed in unison; and a third model, proposed more recently, suggests that climate change occurred first in the Southern Hemisphere. Now new research, published today in the journal Nature, offers support to idea number two: the hemispheres experienced the fluxes hand in hand.

University of Cincinnati geologist Thomas Lowell and his colleagues extracted sediment cores from three lakes in southern Chile. Analyses of the cores' pollen records, which tracked changes in local vegetation between 13,000 and 10,000 years ago, yielded unanimous results: climate change in Chile matched the pattern and timing of warming and cooling in the North Atlantic.

The team selected the Lake District on the basis of its geography and geology, which make it highly unlikely that the region was affected by Northern Hemisphere climate shifts. "If we find similar climate patterns in this region, that indicates the cause must be something global or atmospheric in nature," Lowell notes. "The North Atlantic ice sheets and iceberg 'armadas' could not be the driving force."

"Our results suggest that mid-latitude climate in the Southern Hemisphere changed in unison with the North Atlantic region," Lowell observes. "We are continuing to verify that pattern with an ongoing study in New Zealand.