Justin Stroup is a PhD candidate in the Department of Earth Sciences.
When most people think of glaciers, locations in the Arctic and Antarctic come to mind; however, they also exist in the tropics at high altitudes. Glaciers are excellent indicators of climate change because they are particularly sensitive to changes in temperature and precipitation, and can provide unique histories of climate. The heat in the tropics is circulated globally by the oceans and atmosphere and provide critical information for climate studies. Despite this, the tropics are much less studied than other locations on the globe. The Quelccaya Ice Cap in Peru is the largest tropical ice mass and I am studying how it has changed in size over time as a way to understand past climate change. Specifically, I am interested in the climate of the last 11,600 years, known as the Holocene time, which is climatically most similar to the conditions in which we live today.
Quelccaya is an ideal location for study because there are two different indicators of past climate. First, ice cores, cylinders of ice drilled into the ice cap by Dr. Lonnie Thompson, from Ohio State, provide records of past temperature, precipitation and dustiness. Second, glacial landforms on the landscape around Quelccaya indicate past ice cap size. Dr. Meredith Kelly, a professor at Dartmouth College, and I have studied and dated these landforms. However, there are difficulties using these records to determine Holocene climate. The Quelccaya ice core only provides 1800 years of information and the glacial deposits provide only a few snapshots of ice cap size through time. To overcome these challenges, I am developing long continuous records of climate based on changes in ancient sediment preserved in layers at the bottom of lakes. I am studying a lake fed by meltwater from Quelccaya ice cap. This meltwater transports sediment from the glacier into the lake and thus, changes in ice cap size are likely to influence the layers of sediment in the lake through time.
This project addresses two key issues. First, I am working to determine what pattern of sedimentary layers in lakes fed by glacier melt correspond to glacial advance and retreat. Quelccaya is one of only a few locations in the world suited to make this determination because the sedimentary layers can be interpreted using data from the existing ice core records and ages of glacial landforms. Using these records I will be able to develop a comprehensive reconstruction of the changes in size of Quelccaya and infer the past climate at Quelccaya through the Holocene. Comparison of the climate records from Quelccaya with other climate records from the tropics and around the globe will help our understanding of Holocene climate.
The generous support of the Alumni Research Award provided funding for additional radiocarbon ages. These ages were critical for dating sedimentary layers in the lake cores that represent changing environmental conditions associated with ice cap advance and retreat. The additional ages increased the resolution of my work allowing me to compare the lake sediment record confidently with the ice core records and glacial deposits from Quelccaya. These comparisons improve the tools for interpreting lake sediment records and our understanding of Holocene climate in the tropics and across the globe.