Scientists pull a record 700,000 years of tropical climate change from Andean lake bottoms

When Mark Abbott and his team pulled a 300-foot-long mud core from the bottom of a high lake in the Peruvian Andes, he hoped it could provide a glimpse into the last 160,000 years of climate change.

Instead, the researchers revealed July 13 in the journal Nature, that the lake floor recorded glacier tides for more than 700,000 years – the longest glacier record for the tropics, and among the longest historical climate records, full point. In the lake’s mud, a multi-agency team found clues about how climate change could shape the modern world.

“This is unlike anything we’ve had before,” said Abbott, a professor of geology and environmental sciences at the Kenneth P. Dietrich School of Arts and Sciences at the University of Pittsburgh. “We now have a land-based record of glaciation from the tropics that is in many ways the same as our record from polar ice caps and from the oceans, and it’s really lacking.”

Researchers have known for decades that Lake Junin is a rare gem. Located more than 13,000 feet above sea level in the Andes, the lake meets all the right conditions to archive a changing glacial age: Close enough to the glacier that it catches sediment and water flowing down the mountains, but far enough not to be overpowered by the glacier itself. since it was formed. After avoiding being disturbed by thousands of years of churning ice, the lake’s sediments continue to pile up over the years they are laid out like the pages of a history book.

Actually accessing that historical record, however, took researchers more than 20 years.

“It’s remote, high and hard to reach,” said Abbott, who also serves as director of the Dietrich School’s Center for Climate Change and Global. “There are no boats on the lake, and it’s surrounded by marshes — it’s a very difficult site to work on with heavy equipment, so it was a huge effort to put it together.”

The team included researchers from Union College, the University of Florida and a number of other academic institutions. Seven Pitt graduate students and postdoctoral researchers were also co-authors on the paper and assisted with the fieldwork and subsequent analysis.

With a long and detailed record of climate change in the tropics, the team was able to compare the history of global climate change in a way that was previously impossible. The history of the glaciers contained in the lake’s core matches that found elsewhere, suggesting a cycle of about 100,000 years in the amount of ice around the world. But it also expressed some curiosity.

“What we’re trying to do here is relate this to records at the poles and oceans and see how they differ over time,” Abbott said. For example, “there was a period between about 400,000 to 200,000 years ago where it appears that the tropics were wetter than the poles.”

Reading the records meant dividing the 300-foot-long core into thousands of pieces and carefully shearing and studying the layers of sediment. Layer makeup reveals how it was formed – whether glaciers rub against rock or lakes drying up to form wetlands, each process leaves its own distinct trail.

Analyzing the geochemical and magnetic properties of sediments allows researchers to know how temperature and precipitation change over time. The team also used several methods, including radiocarbon dating done by PhD student geology Pitt and environmental science Arielle Woods, to determine when each layer was deposited.

Comparing 700,000 years of climate change from Lake Junin with those found elsewhere in the world reveals patterns that could serve as clues to what to expect as the world warms up in the 21st century. “As the Arctic warms, the southern tropics dry up dramatically. You shift the heat to the southern hemisphere, and the monsoon weakens, effectively, so you get very dry conditions,” Abbott said.

That is very important because of how many people rely on predictions of the rainy season to grow crops. And that’s yet another testament to an idea familiar to anyone who studies the planet’s climate.

“Global climate is very much related,” he said. “If you change something anywhere in the world, you see the effect almost everywhere.”

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