Continuous-Flow Analysis of δ17O, δ18O, and δD of H2O on an Ice Core from the South Pole
Eric J. Steig, Tyler R. Jones, Andrew J. Schauer, Emma C. Kahle, Valerie Morris, Bruce H. Vaughn, Lindsey Davidge, James W. C. White
Abstract
The δ D and δ 18 O values of water are key measurements in polar ice-core research, owing to their strong and well-understood relationship with local temperature. Deuterium excess, d , the deviation from the average linear relationship between δ D and δ 18 O, is also commonly used to provide information about the oceanic moisture sources where polar precipitation originates. Measurements of δ 17 O and “ 17 O excess” (Δ 17 O) are also of interest because of their potential to provide information complementary to d . Such measurements are challenging because of the greater precision required, particularly for Δ 17 O. Here, high-precision measurements are reported for δ 17 O, δ 18 O, and δ D on a new ice core from the South Pole, using a continuous-flow measurement system coupled to two cavity ring-down laser spectroscopy instruments. Replicate measurements show that at 0.5 cm resolution, external precision is ∼0.2‰ for δ 17 O and δ 18 O, and ∼1‰ for δ D. For Δ 17 O, achieving external precision of <0.01‰ requires depth averages of ∼50 cm. The resulting ∼54,000-year record of the complete oxygen and hydrogen isotope ratios from the South Pole ice core is discussed. The time series of Δ 17 O variations from the South Pole shows significant millennial-scale variability, and is correlated with the logarithmic formulation of deuterium excess ( d ln ), but not the traditional linear formulation ( d ).