| Summary: | Advisors: Nathan D. Stansell. Committee members: Justin P. Dodd; Byron A. Steinman. Includes bibliographical references. Includes illustrations and maps. Guatemala is a drought-sensitive country that experiences varying amounts of precipitation in response to Atlantic and Pacific Ocean influences. A 5.5 m, finely-laminated sediment core from Lake San Francisco in the Huehuetenango province was collected in order to reconstruct precipitation changes over the last ~5,200 years at a decadal-scale resolution. An age-depth model was developed based on 7 radiocarbon ages of charcoal as well as ²¹⁰Pb dating of surface sediments. Authigenic calcite preserved in the sediment record provides an archive of lake-water isotopic variability in response to climate driven changes in hydrologic balance. Modern surface water isotope data taken from lakes throughout the region do not indicate evaporative enrichment relative to meteoric water. Within open-basin lakes within the Tropics, such as San Francisco, δ¹⁸O variation is often driven by the amount effect. This means that high δ¹⁸O reflects drier conditions within the record while lower δ¹⁸O values indicate wetter overall periods. Our data suggest relatively dry conditions within the region between 5-2 ka BP, with the driest period lasting from ~4.2 to ~3.2 ka. A shift to wetter conditions began at ~2 ka and persisted until the past century. Correspondence between the San Francisco record and both North Atlantic Oscillation (NAO) and El Niño Southern Oscillation (ENSO) reconstructions suggest that both of these modes of variability drive precipitation change in this region of Guatemala. In general, positive (negative) phases of ENSO cause drier (wetter) conditions, while positive (negative) phases of NAO cause wetter (drier) conditions throughout the duration of the record. The detailed stratigraphy and well-resolved age model exhibited by the San Francisco record indicate a high potential to produce detailed paleoclimate data from Western Guatemala. M.S. (Master of Science)
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