Date of Award
Program or Major
Earth and Environmental Sciences
Doctor of Philosophy
Dork L Sahagian
Speleothems are emerging as important and detailed chronological records of environmental change. Integrating exploration of modern speleothem records of environmental variability, related forcing factors, and understanding and suggests new potential proxies. This dissertation demonstrates the potential for developing novel proxy records of past regional environmental extremes, such as tropical cyclones, explosive volcanism, and enhanced seasonal contrasts from speleothems that are sensitive to transient infiltration events through very high-resolution, multi-parameter analysis of a rapidly growing, fracture-fed tropical stalagmite. A series of sample screening steps were developed prior to stalagmite collection in the field in order to increase the likelihood of collecting suitable samples sensitive to tropical cyclone precipitation events. Once the correct annual dating was established for a recent period (2001-1978), a weekly-monthly record of stalagmite stable isotope ratios showed low stable oxygen isotope excursions that corresponded to the historical record of tropical storm strikes in the region. Furthermore, excursion amplitude was related to the maximum intensity of storms prior to landfall. The same stalagmite contains a trace element record of the El Chichon eruption, validated by both Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) and Scanning X-ray Fluorescence (S-XRF). A dominant, broad spectrum trace element perturbation was recorded by both methods at 1982, coincident with a major explosive eruption of the nearby trachy-andesite El Chichon volcano in Chiapas, Mexico in April of that year. This result demonstrates the ability of stalagmites to record proxy evidence of a major regional tephra fallout event. The LA-ICPMS technique showed greater discriminating power between volcanic and extensive rainfall signals. A lag correlation analysis of weak El Nino forcing in Belize using a large suite of meteorological and satellite datasets required removal of seasonal variance in order to detect any El Nino response. Individual variables responded independently to El Nino, and no coherent lag timescale was evident. Analysis of biological factors including the belowground community will be required to assess the non-linear processes linking small changes in temperature and moisture extremes to large carbon isotope variations. Promising new proxies for tropical cyclone activity and low-latitude explosive volcanism may emerge from this work.
Frappier, Amy E Benoit, "Recent extreme events in a tropical stalagmite: Multi-proxy records and analysis of ecosystem delta carbon-13 value sensitivity to weak climate forcing" (2006). Doctoral Dissertations. 338.