UMass professor gives talk on climate change in ancient Africa

Dr. Castaneda, the assistant professor of geosciences at the University of Massachusetts, is giving a talk entitled "Vegetation and climate change in southern East Africa During the past 800,000 years." (Zhelun Lang/The Daily Campus)

For Isla Castañada, an assistant professor in the Department of Geological Sciences at UMass Amherst, the African earth is a historic archive, rich with untapped information on what our planet was like 800,000 years ago or more.

In a lecture Castañada gave Tuesday morning titled “Vegetation and climate change in southern East Africa during the past 800,000 years: Insights from organic geochemical proxies,” she talked about how certain variables could help scientists, like herself, understand what the climate of the planet was like hundreds of thousands of years ago, when cycles of freezing and thawing took their course.

“I’m interested in studying warm intervals in history to know more about future warming due to climate change,” she said.

Castañada said ancient patterns of climate change can help us understand present and future patterns of climate change.

She called the variables of her study “proxies”, which are indirect ways of determining past environmental conditions. The proxies she used to understand past climatic conditions in southern East Africa included plant material packed and stored in cores that were extracted from the region. By looking at the way the chemistry of organic substances like plant matter change from the deepest part of the core to the shallowest, Castañada is able to understand the changes in climate that took place or how living things reacted to those changes.

“Molecules of organisms change based on the temperature,” she said.

Southern East Africa is situated in a part of the world where the very first humans and human-like species roamed. Knowledge of the climate in those ancient times could be used in many disciplines, including anthropology, to understand how humans migrated and how climates affected them. The first step, Castañada said, is to figure out what the environment back then was like.

Castañada’s research using organic matter has looked at two kinds of plants – C3 and C4 – which are different in the way they take up the carbon in the air. This carbon can be measured in leaf waxes, which plants make to help them retain moisture and for protection. C4 plants are much better at taking up water than C3 plants, so the ratio of C3 and C4 plants detected in cores can tell scientists about the patterns of precipitation thousands of years ago.

About 430,000 years ago, Castañada said, there was an event called the Mid-Brunhes Event, when carbon dioxide concentrations in the air became much higher. Whether the event was regional or global is still contested by some scientists, but Castañada’s research shows that there was such an event in southern East Africa.

She explained the process of her research, which begins by dividing the core extracted from the region into samples. Then, a solvent is used to extract lipids (fats) from the samples. Lipids, unlike DNA, last much longer and are a more reliable way of looking at ancient living things.

“This machine is a $400,000 coffee maker,” Castañada said as she talked about the device used to extract lipids and other substances from samples.  

At the end of the process, a series of small tubes containing samples are analyzed to figure out how the chemistry changed and how those changes correspond to changes in climate determined from previous work using different proxies.

Her research has resulted in many findings and a better understanding of environmental history of southern East Africa, but there are still many questions that need answering, including whether warm ocean surface temperatures resulted in more precipitation in that region.

“Climate change in that part of the world is going to lead to floods,” she said.


Diler Haji is a staff writer for The Daily Campus and can be reached via email at diler.haji@uconn.edu.