July 13, 2022
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Andean glaciers reacted in unison with polar ice in changing climate

Anne M Stark, stark8 [at] llnl.gov, (925) 422-9799

For the first time, scientists have shown that glaciers in the tropical Andes mountains have been in sync with polar ice extent in Antarctica and the Arctic for nearly a million years.

New research by an international team, including Lawrence Livermore National Laboratory (LLNL) scientist Christine Y. Chen, records glacier movement in the Southern Hemisphere that dates back hundreds of thousands of years and shows that, as drivers of climate change, greenhouse gases are having the same impact on tropical glaciation as in the high latitudes of the Northern Hemisphere.

Until this recent study, which examined sediment from Lake Junín, a lake high in the central Peruvian Andes, most of what scientists knew about past glacial changes came from records of ice growth and decay in the Northern Hemisphere. The research appears in Nature.

Chen, a co-author of the paper, developed the uranium-thorium geochronology of the sediment core, which is the basis for determining the age and duration of the sediments recording local glacial ice extent. “If not for our independent measurements of the uranium and thorium content of these muds, we wouldn’t know how much time the record spans — more than 700,000 years,” she said.

“Scientists have known for nearly a century that rising greenhouse gases will affect the climate in every corner of the world, but we’ve been less certain about how rapidly changes in ice volume at the poles will propagate to the rest of the world,” Chen said. “The high-altitude mountains in the tropics are essentially as far away from the poles one can get. We’ve now shown that ice in both regions has been growing and decaying synchronously with one another for nearly a million years, which further highlights the interconnectedness of our planet.”

The team was able to collect a record of changes that goes back 700,000 years, the longest record ever from the Southern Hemisphere, matching the timeframe of the ice core records from Antarctica.

“As we try to understand how climate works across the globe, we need more than just records that are influenced by and biased toward the Northern Hemisphere,” said Robert Hatfield, an assistant professor in the University of Florida Department of Geological Sciences and second author of the paper.

“What makes our findings unique is that we were able to get a continuous and independently dated record of tropical Alpine glaciation for the first time,” he said. “The key takeaway was that the tropics follow the same beat and same rhythm to what’s going on in the Northern Hemisphere.”

Despite variations in solar radiation between the two hemispheres, the study showed synchroneity among glacier changes in both. This suggests that the rise in atmospheric greenhouse gas concentrations associated with changes in the volume of northern ice sheets is influencing the entire planet within the same timeframe.

When glaciers were extensive in the high Andes, they eroded the mountains around them, sending sediment contained in meltwater to Lake Junin. When the glaciers were gone, that sediment was replaced by carbonate accumulation.

junin drilling
An international team of scientists and technical experts working on the drilling platform floating in Lake Junín, Peru, to collect a 100-meter-long sediment record of glaciation in the tropical Andes. Photo credit: Christine Y. Chen.

To collect their data, the team launched a massive drilling mission at the lake in 2015, funded by the National Science Foundation and the International Continental Scientific Drilling Program. Working around the clock for seven weeks, the group retrieved 100 meters of sediment from the lake’s basin. With the sediment recovered, researchers spent the next few years developing a solid age model.

In 2020, the group published their findings about the age of the sediment and went to work looking at its climate record. Using a combination of mineral magnetism and sediment geochemistry, geologists reconstructed the timing and magnitude of the glacial changes over the 700,000-year time frame.

The work is funded by the National Science Foundation. In addition to Chen and Hatfield, researchers from Union College, University of Pittsburgh, Massachusetts Institute of Technology, Oregon State University, Instituto Nacional de Investigación en Glaciares y Ecosistemas de Montaña in Peru, Florida Institute of Technology, Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas in Spain, University of Albany, Occidental College, University of Michigan, Wilkes University, Ciencias de la Tierra y Clima, Universidad Regional Amazónica Ikiam in Ecuador, University of Minnesota, Large Lakes Observatory and the Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ in Germany also contributed to the project.

Karen Dooley from the University of Florida contributed to this story.