Assessment of Extraterrestrial Tracers Ir, Pt and ³He in Polar Ice Cores

• Main Author: Mehmel, Nicholas C.
• Other Authors: Brook, Edward, Haley, Brian, Graham, David, College of Earth, Ocean, and Atmospheric Sciences
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Antarc*; Antarctica; glacier; Greenland; Taylor Glacier
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4x51hr21j

This thesis focuses on the investigation of extraterrestrial tracers Ir, Pt and 3He in polar ice cores. These tracers may be used to identify characteristics of interplanetary dust particles, and to quantify the flux of extraterrestrial material during impact events, certain volcanic eruptions, and stable background periods. In the first chapter I present novel Ir and Pt concentration records in ice cores from Summit Greenland, spanning the Tambora eruption of 1815 and the Tunguska impact event of 1908. A significant Pt signal is observed within a year of the Tambora eruption, but no observed signal is associated with the Tunguska event. Also presented here is a direct comparison between two established chemical digestion procedures, to assess what portions of the Ir and Pt signal are captured by each. An average Ir concentration of ~0.4 fg/g and average Pt concentration of ~15.7 fg/g are recorded, suggesting a total flux of interplanetary dust particles between 43.5 – 217 metric tons/day on Earth. In the second chapter, I present ³He concentrations in very large ice samples (3+ kg) from Taylor Glacier, Antarctica, and report an average concentration among 7 samples of 5.32 x 10⁻¹⁷ ccSTP/g, with an average ³He/⁴He ratio of 98.77 RA (SD: 34.4 RA), where RA is the atmospheric ³He/⁴He ratio comparable to stratospheric IDPs. Size fraction experiments and magnetic separation experiments were also performed on ³He- bearing particles in ice samples, and several bulk ice samples recorded ³He/⁴He ratios over 200 RA.