10BE DATING OF LAST GLACIAL MAXIMUM MORAINES AND SUBSEQUENT GLACIAL RETREAT IN CHIRRIPÓ NATIONAL PARK, COSTA RICA

Author

Caleb Emeka Okpala, Dartmouth CollegeFollow

Author ORCID Identifier

https://orcid.org/0000-0003-3394-2101

Date of Award

2024

Document Type

Thesis (Master's)

Department or Program

Earth Sciences

First Advisor

Professor Meredith Kelly

Second Advisor

Professor Erich Osterberg

Third Advisor

Professor Jonathan Chipman

Abstract

During the Last Glacial Maximum (LGM; ~26-19 ka) and Termination 1 (~19-12 ka), the expansion and retreat of glaciers across the Southern and Northern Hemispheres, as well as other paleoclimate proxies, document a complex pattern of global climate change. While the timing and magnitude of LGM cooling and subsequent warming is relatively well constrained in mid- and high-latitude regions across both hemispheres, less information is available about climate changes in the tropics. To provide more information about tropical climate conditions during the LGM and Termination 1, I mapped and dated the extents of past glaciers in two valleys in Chirripó National Park, Costa Rica. This region is in the humid inner tropics (10°N-10°S) where temperature is a dominant influence on glacial mass balance, and I use the past glacial extents to infer the timing of tropical temperature changes. I employed glacial geologic mapping and ¹⁰Be surface exposure dating of glacial features to establish a chronology of past glacial extents in Valle Talari and Valle de las Morrenas. I determined twenty-one new ¹⁰Be ages and combined these data with ¹⁰Be ages from Cunningham et al. (2019). ¹⁰Be ages of moraine boulders indicate that glaciers in both valleys reached their maximum, downvalley extents at ~19–18 ka, synchronously with glaciers in higher latitude regions. ¹⁰Be ages of upvalley moraine boulders, as well as bedrock and boulders perched on bedrock, indicate that the glaciers retreated rapidly during Termination 1, and that the valleys were likely ice-free by ~16.7 ka. Together with past glacial extents in other tropical regions, the results suggest that sites across the tropics cooled synchronously with higher latitude regions (during the global LGM), and that tropical warming occurred rapidly during Termination 1.

Recommended Citation

Okpala, Caleb Emeka, "10BE DATING OF LAST GLACIAL MAXIMUM MORAINES AND SUBSEQUENT GLACIAL RETREAT IN CHIRRIPÓ NATIONAL PARK, COSTA RICA" (2024). Dartmouth College Master’s Theses. 188.
https://digitalcommons.dartmouth.edu/masters_theses/188