New chemical stratigraphy over the last millennium for Byrd Station, Antarctica

Abstract

A 164-m-deep, 10 cm diameter, ice core was obtained at Byrd Station surface camp (NBY89), West Antarctica in November 1989. In addition, two 10-m shallow cores were recovered at 14 km and 29 km distances upstream from the main core; 2 m-deep pits were dug at each drilling location. Over 2300 individual samples were analyzed for ionic concentration levels in continuous but selected depth-intervals. Results of study provided a continuous 1360-year chronology for the 164-m core based on multiple cross-correlations of δ¹⁸O, ECM and ionic chemistry data combined with megascopic stratigraphy and physical properties. Average ionic concentration values over the entire core profile are CH₃SO₃^-, 0.08; Cl^-, 1.52; NO₃^-, 0.76; SO₄^2-, 1.10; Na₊, 1.13 and Mg²⁺, 0.30 in μ kg-1. Between 60 m to 164 m, the average HCOO-concentration level is 0.04 μkg_-1. Measurements of NH₄⁺, K⁺ and Ca²⁺ were mostly below instrument detection levels. Except for CH₃SO₃^-, the chemistry curves show no significant trends with time. Excess SO₄^2-reveals distinct seasonal cyclicity over the entire 164 m core but CH₃SO₃^- and NO₃^- concentrations also show seasonal variations, most clearly over the top 2 to 4 m. 25 excess SO₄^2- peaks greater than 5 kg km_-2 are identified as volcanic in origin. 5 prominent excess SO₄^2- volcanic peaks below 90 m are laterally traced to the same time-unit events near the top of the Byrd Station deep core recovered in 1968, thereby establishing a reliable chronological connection between the new NBY89 core data with the older ice core records which extends back to Early Wisconsin age.