Dodd, Justin P.
Ph.D. (Doctor of Philosophy)
Department of Earth, Atmosphere and Environment
The spatial ubiquity of trees in terrestrial ecosystems worldwide facilitates the use of stable isotope research in tree-rings to address a wide-range of interdisciplinary questions related to climate, ecology, archaeology, and hydrology. This dissertation focuses on the development and application of Prosopis tamarugo tree-ring stable isotope records as a paleoclimate proxy for the Atacama Desert, Chile. Current paleoclimate proxies from this region lack the spatial and temporal resolution to quantify a causal mechanism for observed Holocene hydroclimate variability. P. tamarugo tree-ring isotopes provide a high-resolution proxy that facilitates the reconstruction of hydroclimate variability at a regional scale. In order to address this issue, annual and subannual hydrogen ( δ2Hac), oxygen ( δ18Oac) and, carbon ( δ13Cac) isotope records of α-cellulose measured in modern P. tamarugo tree rings are used to evaluate the use of this species for climatic reconstruction. Correlation-based analysis over the past half-century (1954-2016) reveals that tree isotopes record hydroclimate conditions, including changes in vapor-pressure deficit and groundwater isotope variability/depth. Modern groundwater depth was successfully modeled from the δ18Oac and δ2Hac values of modern tree-branch a-cellulose. Based on the modern calibration dataset, tree-ring δ18Oac and δ13Cac values of ancient Prosopis sp. are interpreted as a record of regional hydroclimate variability over the Holocene. A discontinuous record of Prosopis sp. tree-ring δ18Oac and δ13Cac isotopes radiocarbon date between 9,500 and 1,200 years ago. These records provide evidence of changes in relative humidity and groundwater availability (via plant intrinsic-water use efficiency) in the Atacama Desert over the Holocene. There is a steady increase in intrinsic water–use efficiency from the early to late Holocene, indicating a regional reduction in the availability of groundwater resources. δ18Oac-based estimates of relative humidity (h) show increased atmospheric moisture variability beginning 4,900 years ago and continuing through to the present. A strong correlation (r = 0.96) between the average δ18Oac values of the Atacama tree-rings and the high Andean Sajama d18O ice core record provides evidence that water availability in the Atacama Desert is linked with high altitude Andean precipitation over the last 9,500 years. The tree-ring isotope series provide a discontinuous, but annually resolved, proxy that is the highest resolution record yet developed for the Atacama Desert. This research provides evidence that Prosopis sp. trees are high-resolution archives of hydroclimate change and suggests that future exploration of arid-region tree species isotope records could increase the spatial coverage of paleoclimate records worldwide.
Olson, Elizabeth Joy, "Hydrogen, Carbon, and Oxygen Isotopes in Prosopis Sp. Trees: A New Climate Proxy For Holocene Paleoclimate in The atacama Desert, Chile" (2018). Graduate Research Theses & Dissertations. 7507.
Northern Illinois University
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