Deciphering Climate from the Characterization of Ring Width, Carbon, and Oxygen Isotopes in Latewood Tree-Ring Cellulose, Big Thicket National Preserve, Texas, USA

Trees are excellent archives of paleoclimatic information. They can preserve records of past temperature, precipitation, drought, and extreme weather events. The focus of this dissertation is to use tree ring width, carbon isotopes, oxygen isotopes from multiple trees to characterize climate variability and the tree-ring tropical cyclone record. Living longleaf pine trees (Pinus palustris Mill.) were sampled from the Turkey Creek and Big Sandy Creek Units at Big Thicket National Preserve, Texas. Annual tree rings were measured and assigned yearly calendar dates. The latewood portion of each annual ring was shaved with a scalpel, and alpha-cellulose was extracted for carbon and oxygen isotopic analyses. Oxygen isotope records from both sites indicated that individual trees growing in the same stands could vary significantly from each other. The heterogeneity of tree-ring oxygen isotopes was driven by variability in the oxygen isotope composition of soil moisture used for tree growth. Average oxygen isotope chronologies from both sites yielded significant correlations with regional fall (August–October) precipitation (Turkey Creek r = –0.71, p < 0.001; Big Sandy Creek r = –0.62, p < 0.001) and z-index (Turkey Creek r = –0.69, p < 0.001; Big Sandy Creek r = –0.63, p < 0.001). An average carbon isotope chronology from Big Sandy Creek was also significantly correlated with fall precipitation (r = – 0.59, p < 0.001) and z-index (r = –0.57, p < 0.001). Individual trees at both sites did not always record similar tropical cyclone events. A composite tropical cyclone chronology from Turkey Creek identified 58% (7 of 12) of the storms known to have produced rainfall at the site. The Big Sandy Creek composite chronology identified 65% (8 of 12) known storms. Wetter than average years that followed dry years were found to mimic the oxygen isotopic signal associated with tropical cyclone events. Additionally, dry years masked the tropical cyclone signal so that it could not be recorded in tree rings.