This study, the first to offer a high-resolution temperature record for the tropical Andes over the past 16,000 years, provides critical insights that could help scientists better understand and predict future climate impacts in tropical areas. The findings are detailed in the Proceedings of the National Academy of Sciences.
"Usually when we study climate change in the past, we emphasize the Northern Hemisphere or Southern Hemisphere because of the outsized role they play in affecting climates all over the globe," said Boyang Zhao, a scientist in Brown's Department of Earth, Environmental and Planetary Sciences and the study's first author. "One of the biggest questions we are getting at is what are the driving factors behind temperature history in this part of the tropics, so that we can begin to potentially apply that data and knowledge to other tropical regions."
In addition to its implications for the future, the study sheds light on how different parts of the world are interconnected in terms of climate, showing that regional climates are closely tied to global climate shifts.
"Our evidence here suggests that temperatures in this region of the world are more influenced by the Southern Hemisphere - so places like Antarctica," Zhao noted.
The research centered on sediment samples from Laguna Llaviucu, a lake in Ecuador's Cajas National Park. The analysis revealed that temperature variations in the tropical Andes mirrored global climate events over the past 16,000 years, with CO2 levels playing a significant role in these changes. Specifically, the study found that between 17,000 and 14,000 years ago, temperatures in the tropical Andes rose as carbon dioxide levels increased. Similarly, temperatures stabilized around 12,000 years ago when CO2 levels plateaued.
Zhao emphasized that these findings align with earlier research identifying carbon dioxide as a key factor in global temperature changes since the last Ice Age.
The study also explored the role of ocean currents, particularly those transporting warm water from the tropics to the North Atlantic. During the Antarctic Cold Reversal, around 14,500 years ago, these currents intensified, moving more heat northward and cooling sea surface temperatures in the south, which in turn impacted the tropical Andes.
To reconstruct past climate conditions, the researchers utilized lipid biomarkers and hydrogen isotopes from sediment samples collected in 2009 at Laguna Llaviucu by Mark Bush from the Florida Institute of Technology. Lipid biomarkers, which are chemical compounds providing information about past temperatures and rainfall, combined with precise dating methods, allowed the team to construct a detailed timeline of climate changes over the last 16,000 years.
This study marks the first time that organic biomarkers have been used to quantitatively reconstruct a climate history for tropical South America, an area where temperature reconstructions have traditionally been challenging.
The research also highlights regional variations in temperature patterns. For example, while the tropical Andes and Southeast Asia experienced cooling during certain periods, other regions like Africa did not. Additionally, the findings suggest that local factors may counteract global CO2-driven temperature changes, as evidenced by differences between past climate models and the sediment data.
Researchers at Brown University plan to continue their investigation into historical temperature patterns in the tropical Andes, a region that has been underrepresented in climate records.
"Mountain environments are some of the most sensitive regions on Earth to climate change," said James Russell, a professor of Earth, Environmental, and Planetary Sciences at Brown who led the research. "In fact, in the near future, high tropical mountains, such as the Andes, are predicted to experience a rate of warming second only to the Arctic, which is the fastest warming part of the planet."
The study also involved contributions from Brown undergraduate student Aaron Freeman and was supported by the U.S. National Science Foundation.
Research Report:Tropical Andean climate variations since the last deglaciation
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