Investigation of Cryptotephra in Polar Ice Cores

• Main Author: Helmick, Meredith
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2022
• Subjects: tephra; cryptotephra; ice cores; tephrochronology; stratigraphy; volcanology; Glaciology; Other Earth Sciences; Antarctic; The Antarctic; New Zealand; South Pole; Antarc*; ice core; Ice Sheet; South pole
• Online Access: https://digitalcommons.library.umaine.edu/etd/3722; https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=4788&context=etd

Volcanic ash (tephra) present within polar ice cores greatly supplements our understanding of past volcanism and its impacts on society and the state of the climate system. This thesis investigates the utility and limitations of ice core tephrochronology in answering questions related to volcanic source identification of ice core glaciochemical signals, tephrostratigraphy of an Antarctic ice core, and the timing of major and climate forcing eruptions. This thesis explores the efficacy of SEM-EDS measurements on ultra-fine (µm) volcanic particles for the purpose of geochemically characterizing a non-visible ice-embedded tephra and the subsequent identification of the volcanic source. In combination with other lines of evidence, such as the timing and deposition of microparticles and volcanic sulfate to the Antarctic ice sheet at South Pole, we hypothesize that the volcanic source of a dated 1880’s non-visible tephra layer in the South Pole Ice Core can be linked to the 1886 CE eruption of Tarawera, Okataina Volcanic Center, New Zealand. This study also highlights the complexities of volcanic source determinations using ultra-fine particles and SEM-EDS, especially when possible volcanic sources are close in composition, as is the case with eruptive products of the Okataina Volcanic Center and 1883 CE Krakatau. Volcanic source aside, we present the cryptotephra layer discovered at 23.61-23.79 meters depth of the South Pole Ice Core as a potential tephrochronological maker for the correlation of paleoclimate datasets. Geochemical data presented in Appendix B establishes the foundations for a South Pole Ice Core tephrostratigraphic record with novel cryptotephra layers discovered at ~1882 CE, ~1600 CE, ~3518 BCE, ~4526 BCE, ~8127 BCE, and ~9214 BCE (all dates are based on SP19 timescale). Geochemical data presented in Appendix D is the University of Maine’s contribution to a PNAS Nexxus publication. Our analyses of cryptotephra from the GISP2 ice core helped to determine Aniakchak II as the source of a dated 1628 BCE ...