Date of Award

1-1-2023

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (x, 68 pages) : illustrations (some color) ; color maps.

Dissertation/Thesis Chair

Aubrey L Hillman

Committee Members

Sujata Murty

Keywords

Asia, Isotope Geochemistry, Monsoon, Paleoclimate, Paleolimnology, Sedimentology, Precipitation (Meteorology), Monsoons, Hydrologic cycle, Paleoclimatology, Lakes

Subject Categories

Atmospheric Sciences

Abstract

The delivery of monsoonal precipitation in the face of climate change is a growing concern, especially within regions with high population density and a corresponding demand for freshwater resources. Within these regions, the monsoon season can deliver more than half of the annual freshwater for the area. Regional climate dynamics controlling these precipitation patterns within the Holocene (11.7 kyr BP−present) are poorly understood and difficult to differentiate within a single climate proxy from a single site. However, by cross referencing different proxies within a given region we can begin to discern general trends in precipitation dynamics on centennial and multi−centennial cycles.This research seeks to: 1) explore what causes centennial and multi−decadal variations in lake level at Lake Yilong and 2) improve our understanding of the contributions of human modifications to water balance at Lake Yilong. Lake Yilong, which provides a record from 10 kyr BP to present, can provide further insight into what causes shifts in the mean state of the Indian Summer Monsoon (ISM) on centennial scales, and how this region within the Yunnan Province of China differs from other regions. It is hypothesized that we will see changes in the lake level resulting from changes in the mean−state of the Indian Ocean Dipole (IOD). This influence will be present as sediment δ18O values reflecting shifts in lake precipitation−evaporation balance as the result of changes in IOD. We also hypothesize that Lake Yilong will reveal human influences later within the Holocene compared to lakes located closer to the province’s capital, Kunming. To test these hypotheses, we analyzed organic matter and carbonate percentages, δ18O and δ13C values of carbonate material, as well as x−ray diffraction (XRD) and scanning electron microscope (SEM) mineralogical identifications to reconstruct a 10,000−year record of paleoclimate in the Yunnan Province of China. We also ran computational lake hydrologic balance models with δ18O values to provide further insight into lake sensitivity to climate parameters. This study indicates that lake hydrologic balance throughout the Holocene is strongly influenced by Indian Ocean sea surface temperatures, insolation, and the resulting changes to precipitation−evaporation balance throughout Yunnan Province. It is also apparent that human influences are affecting the lake in the late Holocene as displayed in the overlap of change in sedimentology and the timing of rice paddy cultivation.

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