Date of Award

Summer 9-15-2022

Document Type

Thesis (Master's)

Department or Program

Earth Sciences

First Advisor

Meredith Kelly

Abstract

Reconstructions of past glacial extents using geomorphic mapping and cosmogenic dating provide an opportunity to infer past climates. A record of the past extents of tropical mountain glaciers is particularly useful because there are few other means to reconstruct past temperatures in high-altitude, low-latitude locations. The tropics play an outsized role in mediating global climate, yet there is a lack of understanding of how the tropics may have influenced past climate changes such as the most recent deglaciation (Termination 1, ~18–11.7 ka). Improving reconstructions of tropical mountain glaciers will aid in understanding the role of the tropics in the global climate system.

Here, I use records of past glacial extents from three valleys in the Sierra Nevada del Cocuy, Colombia, to construct a temperature record from the region during Termination 1. I present 33 10Be ages from the Bocatoma and Lagunillas valleys and combine these new data with similar data from prior work in the Ritacuba Negro valley (Jomelli et al., 2014, 2017). 10Be ages indicate that glaciers in the valleys advanced during two intervals, ~14–13 ka and ~12–11 ka, and retreated rapidly at ~11 ka. Temperature reconstructions derived from glacier equilibrium line altitude reconstructions suggest that Cocuy was at most ~1.5–3°C cooler from ~18 to 11 ka and that temperature increased by approximately 1°C at ~11 ka. A comparison of the Cocuy glacier-based temperature reconstructions with tropical sea surface temperature records and higher-latitude records suggests that there is no consistent hemispheric or oceanic influence on Cocuy temperatures. The TraCE-21ka model closely replicates the land surface temperatures inferred over Cocuy. This project adds a crucial land surface temperature record from the northern tropical Andes during Termination 1. Increasing the resolution of tropical temperature records is crucial to better ascertain the influence of the tropics on global climate system during periods of abrupt climate change.

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