PALEOTEMPERATURE, VEGETATION CHANGE, FIRE HISTORY, AND LAKE PRODUCTIVITY FOR THE LAST 14,500 YEARS AT GOLD LAKE, PACIFIC NORTHWEST, USA

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dc.contributor.advisorGavin, Daniel
dc.contributor.authorBaig, Jamila
dc.date.accessioned2024-01-09T21:08:59Z
dc.date.available2024-01-09T21:08:59Z
dc.date.issued2024-01-09
dc.description.abstractThe postglacial history of vegetation, wildfire, and climate in the Cascade Range (Oregon) is only partly understood. This study uses high-resolution analysis from a 13-meter, 14,500-year sediment core from Gold Lake to reconstruct forest vegetation, fire, and climate using four traditional palaeoecological methods: pollen, charcoal, organic matter variables, and a biological variable chironomid (midges living in the lake). As the response of these proxies differs, this multiproxy approach is vital to have a complete picture of past environments. The occurrence of three tephra layers, including a 78-cm air fall Mazama tephra and highly laminated segments, allows us to study tephra impacts at a fine temporal resolution. This study is the first attempt in Oregon to reconstruct paleotemperature using chironomids.The high-resolution macroscopic charcoal and pollen analysis reveals that there is minimal variation in pollen spectra during the Late Glacial and Younger Dryas periods. However, the early Holocene shows a sudden increase in Pseudotsuga, indicating warmer conditions, while the late Holocene shows an increase in Tsuga heterophylla and Tsuga mertensiana, suggesting the onset of moist conditions. The charcoal data indicate periods of large fire peaks during the Late Glacial, pre-, and post-Mazama eruption and since 4,000 years ago. Surprisingly, low fire activity is observed during the early Holocene, which contradicts expectations based on regional evidence of warmer and drier summers. The deposition of the Mazama tephra resulted in changes to the non-arboreal pollen composition, while arboreal taxa were minimally affected. The paleotemperature reconstruction reveals variations in the taxon richness of chironomids. The reconstructed midge-based mean July air temperature (MJAT) at Gold Lake ranged between 9.4 and 13.2°C, with the Late Glacial period being 2-3°C colder than present. The transition into the early Holocene indicates a temperature increase with MJAT varying between 10.7°C and 13.1°C. The analysis of organic geochemistry reveals variability in δ13Corg and δ15N, reflecting changes in aquatic productivity. The base of the core following deglaciation shows low terrestrial input and high aquatic productivity, while the Holocene warming period is associated with decreased δ15N and increased input from cyanobacteria. The thick Mazama tephra enhances diatom production and subsequent fluctuations in mass accumulation rate. The late Holocene exhibits high aquatic productivity, potentially influenced by increased forest fires and nutrient runoff. This multiproxy approach significantly contributes to understanding climate change and ecosystem dynamics in the Cascade Range of Oregon based on high-resolution analysis of sediment records from Gold Lake. This dissertation is organized into three main chapters that will be published as separate articles/already published by the dissertation defense time.en_US
dc.identifier.urihttps://hdl.handle.net/1794/29083
dc.language.isoen_US
dc.publisherUniversity of Oregon
dc.rightsAll Rights Reserved.
dc.titlePALEOTEMPERATURE, VEGETATION CHANGE, FIRE HISTORY, AND LAKE PRODUCTIVITY FOR THE LAST 14,500 YEARS AT GOLD LAKE, PACIFIC NORTHWEST, USA
dc.typeElectronic Thesis or Dissertation
thesis.degree.disciplineEnvironmental Studies Program
thesis.degree.grantorUniversity of Oregon
thesis.degree.leveldoctoral
thesis.degree.namePh.D.

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