South American Hydroclimate during the Penultimate Glacial Period Determined by Stable Isotope Analysis of a Peruvian Stalagmite

Author

Grace O'Hara, Union College - Schenectady, NYFollow

Date of Award

6-2022

Document Type

Restricted (Opt-Out)

Degree Name

Bachelor of Science

Department

Geology

Second Department

Environmental Science and Policy

First Advisor

David Gillikin

Second Advisor

Donald Rodbell

Abstract

South American climate is influenced primarily by the South American Summer Monsoon (SASM), which operates on decadal cycles with intensities reliant on the position of the intertropical convergence zone (ITCZ) and solar insolation. This study investigates the fluctuations of South American climate that occurred during the penultimate glacial period using the analysis of stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes from a Peruvian stalagmite. Based on uranium/thorium dating, the stalagmite grew between 122,010 - 208,738 years BP, during the glacial period MIS6. The analysis of stable carbon and oxygen isotopes can be used to determine the behavior of climate oscillators that influence the hydroclimate in the Peruvian Andes during the stalagmite growth. δ¹⁸O values indicate precipitation and temperature patterns in the cave and δ¹³C values are influenced by the percolation of precipitation through the epikarst, where the concentration of CO₂ is correlated to precipitation and temperature. Through the comparison of other climate proxies from existing research we observe the relationship between environmental conditions and stable isotopes. The stalagmite isotopic record shows the decoupling between carbon and oxygen values during the glacial period MIS 6, during which increasing δ¹⁸O values suggest a gradual shift from wet to dry conditions occurs over a period of 13,000 years. We would expect δ¹³C values to show the same behavior, however, the values show a sharp increase followed by a gradual decrease, opposite of the oxygen record, suggesting other factors perhaps control carbon isotopes in this stalagmite. As the climate crisis can bring great uncertainty, the study of paleoclimate can be used to predict how climate oscillators will change in response to global warming and ultimately affect the livelihoods of people.

Recommended Citation

O'Hara, Grace, "South American Hydroclimate during the Penultimate Glacial Period Determined by Stable Isotope Analysis of a Peruvian Stalagmite" (2022). Honors Theses. 2568.
https://digitalworks.union.edu/theses/2568