GSA Connects 2021 in Portland, Oregon

Paper No. 111-2
Presentation Time: 1:50 PM


HERBERT, Jordan, Earth Sciences, Dartmouth College, Hanover, NH 03755, KELLY, Meredith, Earth Sciences, Dartmouth College, HB 6105 Fairchild Hall, Hanover, NH 03755, BROMLEY, Gordon, Department of Geography, National University of Ireland, Galway, Ireland, DOUGHTY, Alice, Earth and Climate Sciences, University of Maine, Orono, ME 04469, RUIZ-CARRASCAL, Daniel, International Research Institute for Climate and Society, Columbia University, Palisades, NY 10964, HIDY, Alan J., Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 and RESTREPO-MORENO, Sergio A., Departamento de Geociencias y Medio Ambiente, Universidad Nacional de Colombia, Facultad de Minas, Medellin, 050040, Colombia

Mountain glacier reconstructions using geomorphic mapping and cosmogenic nuclide surface-exposure dating provide an opportunity to infer past climates over time. Applying this methodology in the humid inner tropics, where glacier fluctuations primarily track changes in temperature, allows for the construction of a terrestrial tropical temperature record. The tropics make up over half of Earth’s surface area and play a large role in mediating global climate, yet relatively little is known about their role in the climate changes at the end of the last ice age (i.e., Termination 1; ~19-11 ka). Here we present a record of past mountain glacier extents in the Sierra Nevada del Cocuy, Eastern Andes Cordillera, Colombia, during that time. Using satellite imagery and a digital elevation model, we mapped glacial geomorphologic features and reconstructed the past extents of three glaciers in the Lagunillas and Bocatoma valleys. We used these mapped glacier extents to determine the equilibrium line altitudes (ELAs) of the glaciers based on the accumulation area ratio (AAR) method. We dated moraines using cosmogenic 10Be surface-exposure dating and present 33 ages that will be measured over the next few months. Calculating ΔELA by comparing our reconstructed ELA to a reference ELA and applying a lapse rate allows us to estimate temperature change at certain times. We compare our temperature record to local proxies such as other mountain glacier extents in the tropical Andes as well as sea surface temperature reconstructions from the tropical Pacific and Atlantic oceans. In drawing these comparisons, we aim to improve the understanding of tropical climate change during Termination 1, specifically if there is a coherent signature of temperature change, and whether tropical temperatures changed (a)synchronously with high latitudes. Tropical glaciers have undergone rapid recession in recent decades as a result of warming which is amplified at high altitudes. This project employs these glaciers as a proxy to better understand the role of the tropics in past climate change with the ultimate goal of improving our ability to model and predict future climate change.