Date of Award

6-2020

Document Type

Restricted (Opt-Out)

Degree Name

Bachelor of Science

Department

Geology

First Advisor

Donald Rodbell

Second Advisor

David Gillikin

Keywords

Speleothems, paleoclimatology, Peru, South American Summer Monsoon

Abstract

The South American Summer Monsoon (SASM) system governs the annual hydrologic cycle in the Amazon Basin. It varies on an annual cycle, but recent paleoclimatic records indicate that it may also vary on centennial to multimillennial cycles. Speleothem deposits record isotopic variation over both short and long timescales, and have proven to track Dansgaard-Oeschger (D/O) events, which are defined as abrupt warming periods in the Northern Hemisphere. D/O events are represented in Southern Hemisphere proxies, as they impact SASM strength in the Southern Hemisphere. Huagapo Cave is located in Palcamayo, Peru (11.27˚S; 75.79˚W; 3,850 meters above sea level) and is 2800 meters in length. Twelve speleothem deposits were collected in May of 2019. Samples were dated using the Uranium-Thorium dating technique, and results indicate the time range covered is 2,000 years BP to 440,000 years BP. Time frames not covered include 2,500-25,000 years BP and 227,000-312,000 years BP. One sample, spanning from 63,799 (±119) to 25,021 (±53) years BP, was analyzed for stable oxygen (δ18O) and carbon (δ13C) isotopes to better constrain climatic variability and confirm the reproducibility of one published speleothem record that documents the impact of D/O events in the Peruvian Andes. Preliminary data suggest that the δ18O and δ13C reflect amount effect variations, with strong SASM conditions indicated by decreased δ18O and decreased δ13C that reflect rainfall isotopic concentrations and the respiration of organic matter in surface soil horizons, respectfully. Data from this study shows that the anti-phase relationship between the Northern Hemisphere and Southern Hemisphere climate fluctuations is caused by meridional shifts in the mean position of the Intertropical Convergence Zone (ITCZ), which changes location based on warming in different hemispheres. The increased warming in the Northern Hemisphere during D/O events caused a likely northward shift of the ITCZ, and a corresponding decrease in strength of the SASM in South America.

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