COLLECTION AND DATING OF THE ICE CORE

Because the site was in a designated wilderness area, conventional drilling systems were not allowed. Instead, a solar- powered drill was used. Dust layers in the ice core were occassionally too faint to give reliable annual stratigraphic markers; therefore, chemical age-dating techniques in combination with estimated accumulation and ablation rates were used to construct a low-resolution chronology for generalized climatic interpretation and comparisons. Tritium (³H) concentrations exceeding 300 tritium units (TU) at a depth of 29 m below the surface corresponded to a snowfall deposited in 1963 during the peak of above ground nuclear bomb testing. Carbon-14 (¹⁴ C) age dating of a grasshopper leg entrapped at 152 m below the glacier surface indicated that ice near the bottom of the core formed from snow deposited in the early 1700's A.D. Furthermore, the positions of the tritium and ¹⁴C horizons within the ice core approximate the ages calculated from present-day estimations of average annual snowfall and summer ablation.