Contrasting Responses of Ion Concentration Variations to Atmospheric Patterns in Central Himalayan Ice Cores

Abstract

We analyzed the water-soluble chemical composition of an 81.2-m-long ice core collected in 2019 from $\sim$6,000 m elevation on a south-facing glacier in the Nepal Himalaya. The ice core chronology is based on variability in nitrate and calcium ions, which reveal an apparently seasonal periodicity (with winter maxima) throughout the core's length. Two annual boundaries are consistent with the tritium peak representing nuclear tests conducted in 1963 CE and with the spike in sulfate ions due to the eruption of Krakatau in 1883 CE. The ice core spans 145 years from 1875 to 2019 CE. Dating uncertainties due to the layer counting methodology were estimated as $\pm 1$ year for 1963–2019 CE and $\pm 2$ years for 1875–1963 CE. Comparison with earlier ice cores drilled on the northern side of the Himalayas revealed that the ion components exhibit inverse correlations with two key climatic indices: the North Atlantic Oscillation and Southern Oscillation Index. Composite analysis of reanalysis climate data suggests that these inverse relationships reflect springtime pressure patterns, which show regional differences between the northern and southern sides of the Himalayan range.