Research by a team including Donald T. Rodbell, professor of geology, suggests that diverse regions of the globe have not warmed and cooled in lockstep, as previously thought. Rather, the Southern Hemisphere may have led the higher latitudes in both cooling and warming.
Rodbell is co-author of a paper published in the April 29 issue of Science, “Early Local Last Glacial Maximum in the Tropical Andes.” It chronicles research by Rodbell and colleagues that determined that the local last glacial maximum in the tropical Andes was earlier and less extensive than earlier studies showed.
“We are starting to see, based on this work and other data, that in fact the globe's response to climatic change is more complicated than we thought,” Rodbell said. More will be known as research continues around the globe, he said.
The team used cosmogenic radio nuclide (CRN) dating to show that glaciers in the Southern Hemisphere reached their greatest extent in the last glacial cycle about 34,000 years ago and were retreating about 21,000 years ago.
They gathered samples from glacially deposited boulders on moraines in Peru and Bolivia. The boulders, once exposed to the atmosphere, begin to gather isotopes produced by cosmic rays. By measuring the accumulation of the isotopes – in this case, beryllium-10 – the scientists could determine when the glacier retreated and exposed the boulders.
The analysis was done at the Center for Accelerator Mass Spectrometry at the Lawrence Livermore National Laboratory in California. The field work took place between 1999 and 2003.
Lead author of the Science paper (No. 15) is Jacqueline Smith, a Ph.D. student at Syracuse University who is married to John Garver, Union professor of geology. Others, besides Rodbell, are the late Geoffrey Seltzer of Syracuse; and Daniel Farber and Robert Finkel of Lawrence Livermore.
Rodbell, whose research focuses on the climate record for the Southern Hemisphere, has been published five times in Science and once in Nature. He recently received the latest in a series of research grants from the National Science Foundation. A number of Union undergraduates have assisted in his fieldwork and laboratory analysis. Three were involved in the project detailed in the current Science paper.