A 25,000-Year History of the South American Monsoon

Exchange student Valdir Novello worked as part of Mathias Vuille's research team to investigate 25,000 years of South American monsoons by examining deposits found in Brazilian caves.

ALBANY, N.Y. (May 1, 2017) – For years, atmospheric scientists have been able to use historical data to determine when the last ice age ended, or when the Earth experienced massive volcanic eruptions. For atmospheric scientist Mathias Vuille, bridging the gap between modern climate dynamics and paleoclimatic interpretation of proxy data is a critical element to the study of weather, and what long-term climate changes we may expect in our future.

Now Vuille, a professor in UAlbany’s Department of Atmospheric and Environmental Sciences, and colleagues from universities in the United States, Brazil and China have developed a high-resolution reconstruction of the South American monsoon system for the last 25,000 years.

The study was lead by Brazilian Ph.D. student Valdir Novello, who developed the record in the lab of his adviser professor, Francisco Cruz, at the University of Sao Paulo, before joining Mathias Vuille’s research group at UAlbany to diagnose and interpret the record and write up his results.

Publishing in Scientific Reports, “This new record provides the best-resolved and most accurately constrained geochronology of any proxy from South America for this time period,” said Novello.

Professor of Atmospheric and Environmental Sciences Mathias Vuille

Using high-resolution “speleothem” (stalagmite) records – calcite deposits formed in caves – the team of researchers was able to reconstruct the strength of the monsoon for South America spanning from before the Last Glacial Maximum (about 24,500 years ago) to the mid-Holocene (about 5,000 years ago).

"There really hasn’t been much research completed that documents changes in the hydrologic cycle in South America from the ice age to the modern era,” said Vuille. “Similarly, our understanding of millennial-scale variability and abrupt changes in South American precipitation during this transition from glacial to interglacial conditions is still rudimentary.”

Without a historical record to go on, it becomes difficult to anticipate how and when abrupt changes in monsoon patterns may occur in the future. Similar to other parts of the world, communities may rely on the predictability of monsoons to determine the availability of drinking water or irrigation for farming. Vegetation in the Amazon also depends on the rains of the South American monsoon season for thriving.

In order to confirm their findings, Vuille and his colleagues also analyzed data from similar time periods in China.

Among their findings, Vuille, Novello and their team found some key weather events in South America’s history appear to match up with global climate changes taking place elsewhere, but the reason for the changes may be different than previously thought.

For instance, their record suggests that the South American Monsoon System (SAMS) was weakened during the Antarctic Cold Reversal (ACR), an important cooling event following the end of the last ice age. The advance of tropical glaciers during this time period was therefore likely due to colder temperatures associated with the ACR, rather than due to increased snowfall associated with enhanced available moisture from the SAMS.

Vuille and Novello collaborated on this project with researchers from Universidade de São Paulo, Universidade Federal Fluminense in Rio de Janeiro, the University of Minnesota, Xi’an Jiaotong University (Xian, China), and the Universidade de Brasília.

The study was funded in part through the National Sciences Foundation (NSF) Paleo Perspectives on Climate Change program.

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