A record of explosive eruptions over the last 1830 years reconstructed from a South Pole, Antarctica, ice core extends the coverage of volcanic history to the start of the first millennium A.D. The ice core dating by annual layer counting carries an uncertainty of ±2% of the number of years from time markers, with the largest dating error of ±20 years at the bottom of the 182 m core. Several aspects of the methodology of detecting and quantifying volcanic sulfate signals in ice cores are examined in developing this record. The new record is remarkably consistent with previous South Pole records. A comparison with records from several Antarctica locations suggests that the South Pole location is among the best for ice core reconstruction of volcanic records, owing to the excellent preservation of volcanic signals at the South Pole, the relatively low and uniform sulfate background, and the moderately high snow accumulation rates which allow for dating by annual layer counting. A prominent volcanic event dated at 531(±15) A.D., along with evidence from other records, indicates that an unusually large eruption took place in the tropics and was probably responsible for the “mystery cloud” climate episode of 536–537 A.D. The date of 536 is suggested for a prominent volcanic signal that appears in the first half of the sixth century A.D. in ice cores, which can in turn be used as a time stratigraphic marker in dating ice cores by annual layer counting or by computing average accumulation rates or layer thicknesses with such markers.

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Measurement of trace chemical impurities in ice cores contributes to the reconstruction of records of the atmospheric environment and of the climate system. Ion chromatography (IC) is an effective analytical technique for ionic species in ice cores but has been used on discretely prepared ice samples, resulting in extensive and slow sample preparation and potential for contamination. A new technique has been developed that utilizes IC as the online detection technique in a melter-based continuous flow system for quantitative determination of major ionic chemical impurities. The system, called CFA-IC for continuous flow analysis with ion chromatography detection, consists of an ice core melter, several ion chromatographs, and an interface that distributes meltwater to the IC instruments. The CFA-IC technique combines the accuracy, precision, and ease of use of IC measurement with the enhanced speed and depth resolution of continuous melting systems and is capable of virtually continuous, high-speed and high-resolution chemical analysis of long ice cores. The new technique and operating procedures have been tested and validated with the analysis of over 100 m of ice cores from Antarctica. The current CFA-IC system provides an all-major-ion analysis speed of up to 8 m a day at a depth resolution of approximately 2 cm.