A new research has determined that Ice Age climate records from an Arizona stalagmite link the Southwest's winter precipitation to temperatures in the North Atlantic. This finding is the first to document that the abrupt changes in Ice Age climate known from Greenland also occurred in the southwestern US.
"It's a new picture of the climate in the Southwest during the last Ice Age," said Julia E. Cole of the University of Arizona (UA) in Tucson.
"When it was cold in Greenland, it was wet here, and when it was warm in Greenland, it was dry here," she added.
The researchers tapped into the natural climate archives recorded in a stalagmite from a limestone cave in southern Arizona.
Stalagmites grow up from cave floors.
"The researchers chose the particular stalagmite for study because it was deep enough in the cave that the humidity was always high, an important condition for preservation of climate records," Cole said.
The stalagmite yielded an almost continuous, century-by-century climate record spanning 55,000 to 11,000 years ago.
During that time, ice sheets covered much of North America, and the Southwest was cooler and wetter than it is now.
Cole and her colleagues found that the Southwest flip-flopped between wet and dry periods during the period studied.
"Each climate regime lasted from a few hundred years to more than one thousand years," said Cole.
In many cases, the transition from wet to dry or vice versa took less than 200 years.
"These changes are part of a global pattern of abrupt changes that were first documented in Greenland ice cores," said Cole. "No one had documented those changes in the Southwest before," she added.
Scientists suggest that changes in the northern Atlantic Ocean's circulation drove the changes in Greenland's Ice Age climate, according to Cole.
"Those changes resulted in atmospheric changes that pushed around the Southwest's climate," she said.
She added that observations from the 20th and 21st centuries link modern-day alterations in the North Atlantic's temperature with changes in the storm track that controls the Southwest's winter precipitation.
"Also, changes in the storm track are the kinds of changes we expect to see in a warming world," she said.
By matching the stalagmite's growth timeline with the sequence of wet and dry periods revealed by the oxygen analyses, the researchers could tell in century-by-century detail when the Southwest was wet and when it was dry.
"This work shows the promise of caves to providing climate records for the Southwest. It's a new kind of climate record for this region," Cole said.