High-resolution ice cores from US ITASE (West Antarctica): development and validation of chronologies and determination of precision and accuracy

Abstract Shallow ice cores were obtained from widely distributed sites across the West Antarctic ice sheet, as part of the United States portion of the International Trans-Antarctic Scientific Expedition (US ITASE) program. The US ITASE cores have been dated by annual-layer counting, primarily through the identification of summer peaks in non-sea-salt sulfate (nssSO4 2–) concentration. Absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores, Tambora, Indonesia (1815), being the most prominent. Independent validation is provided by the tracing of isochronal layers from site to site using high-frequency ice-penetrating radar observations, and by the timing of mid-winter warming events in stable-isotope ratios, which demonstrate significantly better than 1 year accuracy in the last 20 years. Dating precision to ±1 month is demonstrated by the occurrence of summer nitrate peaks and stable-isotope ratios in phase with nssSO4 2–, and winter-time sea-salt peaks out of phase, with phase variation of <1 month. Dating precision and accuracy are uniform with depth, for at least the last 100 years.

摘要 作为国际横穿南极科学考察（美国ITASE）计划中美国部分的一项内容，在西南极冰盖广泛分布的地点获取了浅冰芯。美国ITASE冰芯已通过年层计数确定了年代，主要是通过识别非海盐硫酸盐（nssSO4 2–）浓度的夏季峰值。通过在每个冰芯中识别多个火山标记层（印度尼西亚坦博拉火山（1815年）最为显著），证明了绝对定年精度优于2年，相对定年精度优于1年。利用高频透冰雷达观测追踪不同地点的等时层，以及通过稳定同位素比值中的仲冬变暖事件的时间，提供了独立验证，这表明在过去20年中精度显著优于1年。夏季硝酸盐峰值以及与nssSO4 2–同相的稳定同位素比值，以及与冬季海盐峰值异相（相位变化<1个月）的出现，证明了定年精度可达±1个月。至少在过去100年中，定年精度和准确性随深度保持一致。