Dust Record from Allan Hills Blue Ice: Towards Extending the Archive to 4000 ka

Abstract. Previous analyses of dust concentration and size distribution in ice cores are limited to the past 800,000 years; however, the ALHIC1901 ice core drilled at the Allan Hills Blue Ice Area (BIA) in East Antarctica provides a unique opportunity to examine older discontinuous records of ice ranging in age from 4000–500 ka. Here we present a discrete record of insoluble particles within ALHIC1901 from the bottom 25 m of the core. We investigated the particle mass concentration, size distribution, and mineralogy within the core to assess the preservation of dust records in BIAs with complex flow histories. We find that the insoluble particle concentrations are likely altered by entrainment of basal sediment for depths 5 m above bedrock. For shallower depths less affected by subglacial input, the record lacks expected peaks in dust concentration during glacial periods, which have been termed “long snapshots,” implying that low net accumulation rates during glacial periods at the Allan Hills BIA results in the preferential loss or attenuation of glacial ice and a corresponding bias toward the preservation of interglacial ice. The dust concentrations may also be further smoothed due to ice thinning. A subset of particles from both the upper and lower ranges of depths analyzed shows evidence of mineral weathering and/or in situ production of secondary minerals, and insoluble particle concentration correlates well with non-atmospherically derived carbon dioxide concentrations. These results highlight the importance of identifying signs of basal ice-rock interactions and/or complicated accumulation and ablation histories as these affect our interpretation of paleoclimate records preserved in ice cores from BIAs.