Jennie Zhu

Date of Graduation

2016

Document Type

Thesis

Degree Type

MA

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

Amy Hessl

Committee Co-Chair

Eungul Lee

Committee Member

Jaime Toro

Abstract

Volcanic eruptions have influenced regional and global climate on annual, interannual, decadal, and multi-decadal time scales. However, past studies have largely focused on the response of global temperature to modern eruptions with the aid of satellite records. This approach limits the number of eruptions that can be studied and restricts our knowledge to relatively small events when compared to the volcanic history of the late Holocene. I used modern climate records to evaluate the effect of recent eruptions on Mongolian climate. I then extended my analysis to the last 2500 years by examining existing and new tree-ring data from Mongolia to understand how volcanic eruptions influence different climatic variables (temperature, moisture, and solar irradiance) in Inner Asia. This study, part of a larger research project on human ecology in Inner Asia, focuses on past volcanic eruptions (600 BCE to 2013 CE) at three sites in north central Mongolia: Solongotyn Davaa (48.3°N, 98.93°E), a temperature-limited site, Khorgo lava (48.17°N, 99.87°E), and Urgaat lava (46.40°N, 101.46°E), both moisture-limited sites. To test how modern eruptions (1959-2012) influenced temperature and precipitation regimes in Mongolia, I used the Grid Analysis and Display System to run composite analyses using Climatic Research Unit 3.21 temperature and 3.21 scPDSI data. Three eruptions were analyzed and both composite analyses suggest that, at each location, temperature and moisture variabilities are statistically insignificant during the year of the eruption. I then used superposed epoch analysis to evaluate how past eruptions affected regional climate by separating temperature, moisture, and solar irradiance variables. Again, the results fell within the 95% confidence limits for years zero to three, suggesting that these large eruptions do not affect temperature, moisture, and solar irradiance as much as once thought. Lastly, I looked at the tree-ring anatomy of individual samples to see if there was any anatomical evidence of an eruption event. Select eruption events are evidenced in tree-rings by the presence of narrow ring-width, false rings, and absent rings without any clear pattern as to why certain events affected tree growth at Khorgo lava and Urgaat lava. Chi-square tests comparing non-eruption years with eruption years show that the number of false rings and absent rings at Khorgo lava, and absent rings at Urgaat lava, is statistically significantly higher in the second year following the eruption, showing some effect on tree-ring growth but not necessarily tree-ring-width. The study calls into question the process of studying volcanic eruptions using tree-rings by showing that the atmosphere may be an intransitive cycle where the effects of volcanic eruptions can be variable and uncertain.

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