Northern and Southern Hemisphere climate changes occurred at nearly the same time during the Earth's last ice ages according to data reported in the Feb. 15 issue of the journal Nature.
George L. Jacobson Jr. and George H. Denton of the University of Maine
The group cored three lakes in southern Chile in hopes of resolving a long-standing question: Were the Northern and Southern Hemisphere glaciations and associated climate changes in sync with each other, or did the climate change in a see-saw pattern with northern ice sheets driving climate change later in the south? More recently, a third pattern was suggested, indicating that climate changed first in the Southern Hemisphere.
To help answer those questions, the group obtained pollen records tracking changes in vegetation from 13,000 years to 10,000 years ago. Lake after lake, the results produced the same pattern. The southern mid-latitudes were warming and cooling at the same time as the North Atlantic.
"All records show the same timing, character, and direction of climate change in the mid-latitudes during the end of the last glacial cycle," said Lowell.
"These events [in Chile] were nearly synchronous with important paleoclimate changes recorded in the North Atlantic region," wrote Moreno, "supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation.
The new data is part of an exhaustive data set with over 500 radiocarbon dates from geological and biological samples taken from the Lake District of Chile. In the present study, Moreno tracked the expansion and contraction of forests of the cold-resistant tree types Nothofagus and Podocarpus nubigena.
The researchers chose the Lake District of southern Chile for their studies, because its geography and geology make it highly unlikely that the region could be directly influenced by the Northern Hemisphere ice sheets and changes in North Atlantic ocean currents. "So, if we find similar climate patterns in this region, that indicates the cause must be something global or atmospheric in nature. The North Atlantic ice sheets and iceberg 'armadas' could not be the driving force," explained Lowell.
The same pattern was seen in climatic warming. Previous research by the same team showed an abrupt withdrawal of Andean piedmont glacier lobes 14,600 years ago at the same time northern ice sheets were retreating.
"Our results suggest that mid-latitude climate in the Southern Hemisphere changed in unison with the North Atlantic region. We are continuing to verify that pattern with an ongoing study in New Zealand," said Lowell.
The research was funded by the National Science Foundation, NOAA, the National Geographic Society, the Geological Society of America, and a Fondecyt grant in Chile.
Lowell is in New Zealand this month continuing his field work.