Date of Award
2025
Document Type
Thesis (Master's)
Department or Program
Earth Sciences
First Advisor
Meredith Kelly
Second Advisor
Alice Doughty
Third Advisor
Erich Osterberg
Abstract
The tropics are a critical part of Earth’s climate system, yet their role in global climate changes such as Quaternary glacial-interglacial cycles is poorly understood. Determining the timing, magnitude and spatial distribution of tropical cooling during the Last Glacial Maximum (LGM; ~26-19 ka) and Termination 1 (19-11.7 ka) is important for understanding the mechanisms that caused the global transition from glacial to interglacial conditions. There is a discrepancy between low-elevation records in the tropics which suggest only moderate cooling during the LGM, and high-elevation tropical records which suggest larger temperature decreases. This discrepancy may highlight an important role of water vapor in glacial-interglacial climate change, however there is a lack of quantitative records of high-elevation tropical temperature during the LGM and Termination 1. Glaciers in the humid inner tropics (~10°N-10°S) respond sensitively to temperature and past tropical glacier extents can provide valuable information about past climate conditions at high elevation. Here, I use past glacial extents to quantify the magnitude of high-elevation temperature change during the LGM and Termination 1 at a site in Costa Rica.
I simulate the extents of past glaciers in Chirripó National Park (9.48°N, 83.48°W) in the Cordillera de Talamanca Range of Costa Rica using a two-dimensional numerical glacier model that incorporates surface energy balance and ice-flow models. I input modern climate variables including temperature, precipitation, lapse rate, short-wave radiation and wind speed, and alter these variables to grow glaciers to mapped and dated extents. My results provide quantitative estimates of temperature, precipitation, and lapse-rates relative to modern during the LGM and Termination 1.
I show that LGM glacial extents require a temperature decrease of 8.2-9.7°C relative to modern with a range of precipitation changes (+100% to -80% relative to modern). Simulations with a temperature decrease of ~7.6°C relative to modern and no change in precipitation result in a completely ice-free landscape, suggesting that this landscape was only marginally glaciated. I compare the results with climate conditions inferred at similar high-elevation sites in the humid inner tropics and show that there was a relatively uniform and large magnitude of LGM cooling and Termination 1 warming.
Recommended Citation
Robbins, Liesel Sue, "Modeling Glaciers to Infer Paleoclimate Conditions During and Following the Last Glacial Maximum in Chirripó National Park, Costa Rica" (2025). Dartmouth College Master’s Theses. 214.
https://digitalcommons.dartmouth.edu/masters_theses/214
