INDIANAPOLIS—An associate professor of earth sciences at the Purdue School of Science at IUPUI received a three-year grant totaling $294,604 from the National Science Foundation to investigate how changes in solar radiation impacted water resources in the tropical Andes over the last 10,000 plus years.
Broxton Bird, Ph.D., and a team of researchers will tentatively travel to Lake Tota in Colombia next year for a month to collect sediment cores to develop proxy records of climate variables, including air temperature, precipitation amounts, isotopes, and lakes levels.
“One of the main questions in South American paleoclimatology is how was climate variability phased between the Northern and Southern Hemispheres,” said Bird. “Orbital theory of climate change states that globally, climate changes should be opposite between the Northern and Southern Hemispheres because changes in Earth’s orbit over long periods (thousands of years) changes where incoming solar radiation (or insolation) is strongest. When insolation is high in the Northern Hemisphere, it’s low in the Southern Hemisphere, and vice versa.”
The research builds upon Bird’s previous work in the Peruvian Andes, where the goal was to reconstruct the changes in the South American monsoon over the last 10,000 years. Bird says it was during that research that it became clear to him and others that there was a significant gap in understanding monsoon dynamics in the Northern Hemisphere Andes.
“What is special about this research is that we will, for the first time, reconstruct proxy records of mean annual temperature, mean annual precipitation, and effective moisture (the balance between precipitation and evaporation) on the same lake sediment archive. We will do so on sediments from Lake Tota, the largest lake in the Colombian Andes and the second largest lake in the Andes at large. This will provide a Northern Hemisphere perspective of Holocene climate change that has not previously been available, which will complement existing records from the Southern Hemisphere Andes,” explained Bird.
Armed with that information, researchers will determine two things: 1) the phasing of the monsoon and effective moisture between the Northern and Southern hemispheres, and 2) determine the relative roles of temperature and precipitation on Andean effective moisture.
The information will also help predict what may happen in the future as the climate rapidly warms.
“This will allow us and others to determine how continued warming is likely to impact water resources in the tropical Andes, which is directly relevant to the more than 300 million people that rely on the South American monsoon for their very way of life. Tropical climate variability also directly impacts the midlatitudes, including North America, through atmospheric connections, so there are implications for how these regions will respond to climate change as well,” said Bird.
The researchers will be collecting sediment cores that could be as much as 40,000 years old.
“Once the cores are collected, my collaborators and I will each work on sub-samples for different analyses. Specifically, we’ll measure pollen, leaf wax hydrogen isotopes, grain size, and sediment geochemistry. We’ll also date the sediments with radiocarbon (14C),” said Bird.
The pollen will be used to determine the mean annual temperature and precipitation. The leaf waxes help determine how much or how little evaporation Lake Tota experienced in the past.
“The grain size and sediment geochemistry (the ratio of carbon to nitrogen, or C/N) will tell us about lake levels. When lake levels are low, the shoreline migrates closer to the middle of the lake, which is where we collect our cores. As a result, larger grain sizes, like sand, are deposited closer to the middle of the lake,” explained Bird. “At the same time, more terrestrial material, like soil and plant matter, can also be deposited closer to the middle of the lake. This terrestrial material has more carbon than nitrogen compared to aquatic vegetation because land plants need carbon to support their woody structures. Therefore, when lake levels were low in the past, we expect to see increased sand and more carbon relative to nitrogen.”
Bird will be assisted by researchers from the University of Washington, St. Louis, University of Minnesota, Duluth, University of Minnesota, Twin Cities, University of Regina, University of Mexico, Universidad del Norte, along with graduate students from all the universities involved and Colombian students.
“I see this as a very meaningful way to significantly advance our understanding of tropical climate variability that will also improve our understanding of Earth’s climate system as a whole. It’s also really leading-edge science. There are no other multi-proxy records like this from the Northern Andes, so there is tremendous potential to learn important and fascinating new information.”