Dust that was deposited at the foot of the Andes Mountains in Argentina over the last 1.15 million years helps explain how wind patterns have shifted and could offer clues of what is to come as the Earth's climate changes, according to new research by a team from South Carolina and Arizona.
Alex Pullen, an assistant professor of environmental engineering and Earth sciences at Clemson University, was part of the team that found Pleistocene-epoch dust in the Tafí del Valle depression on the eastern side of the Andes came from the west and northwest, challenging earlier hypotheses that it blew in from the east and south.
"People thought they understood the wind-dust relationships in the Southern Hemisphere during the Pleistocene," Pullen said. "What we're learning, mostly based on geology, is that it's not as simple as everybody thought."
It's a crucial point because westerly winds play an important role in the complex dynamics that shape the landscape of South America, including which areas receive rain and which become desert.
The winds also influence the circulation of ocean waters that affect the Earth's climate, researchers said. A better understanding of the paleoclimate could help explain the Earth's current climate and predict what it will be like in the future, they said.
The team recently reported its findings in a Nature Communications article titled, "A westerly wind dominated Puna Plateau during deposition of upper Pleistocene loessic sediments in the subtropical Andes, South America."
"This paper demonstrates that there is a home for traditional geologists in understanding modern climate change," said co-author David L. Barbeau, Jr., an associate professor in the School of the Earth, Ocean and Environment at the University of South Carolina.
"In studying this ancient system, we've been able to get some ground truth– some hard data– that scientists can use to try to model and understand different climate systems in the past, in the present and into the future."
The findings led the research team to conclude that the westerly winds in the Pleistocene, likely during cooler intervals like the last Ice Age, were located at a latitude several hundred miles farther north than they are today.
Pinpointing the source of the dust in Tafí del Valle and combining that information with what else is known about the region makes it possible to suggest how winds have changed over time, said Jordan T. Abell a National Science Foundation postdoctoral fellow in the Department of Geosciences at the University of Arizona.
"We've provided additional evidence that it's likely the westerly winds were changing over the last million years, in response to shifting climate, to deliver the dust to this site," he said.
The paper's authors from Clemson were Pullen, who was corresponding author, former undergraduate researchers Austin Bruner and Madison Ward and lecturer Mary Kate Fidler. Those from the University of South Carolina were Barbeau and Andrew L. Leier, both associate professors in the School of the Earth, Ocean and Environment. Abell was the sole author from the Department of Geosciences at the University of Arizona.
The team used a technique called detrital zircon geochronology to compare zircon samples from the Las Carreras section of Tafí del Valle to samples from the Chaco Plain to the east, the extra-Andean areas of Patagonia to the south and the Puna Plateau to the west and northwest.
Researchers found that the Puna Plateau samples were most similar to Tafí del Valle samples, while the samples from the Chaco Plain and extra-Andean areas of Patagonia were a poor fit for Tafí del Valle.
They interpreted the findings to mean that the Puna Plateau contributed a large portion of the detritus deposited during the Pleistocene and Holocene periods, they wrote.
The Pleistocene epoch lasted from about 2.6 million to 11,700 years ago, and the Holocene picked up at that point and runs to the present day.
Barbeau said the research demonstrates the value of employing detrital zircon geochronology to test long-standing hypotheses about the source of sediment, especially wind-driven deposits in South America.
"It opens the door to addressing all kinds of important questions related to paleoclimate, which could in turn help us understand modern climate and future climate and climate changes a little bit better," he said.