A Century Ammonium Record Retrieved From the Central Tibetan Plateau

Abstract

AbstractThe limited observations pose challenges to understanding long‐term variations of atmospheric ammonium () deposition. Glaciers on the margins of the Tibetan Plateau (TP) adjacent to heavily populated regions can capture and preserve unique records of natural and anthropogenic ammonium aerosol. However, relatively little has been known about spatiotemporal variations and anthropogenic influences on ammonium deposition on the central TP. Here, we present a high‐resolution ammonium record spanning the period 1900–2011, reconstructed from the Qiangtang (QT) ice core on the central TP. Empirical orthogonal function and interspecies correlation analysis reveal that has a source and/or transport route that differs from the dust species, especially after the 1950s. The QT ammonium record is also likely influenced by temperature‐dependent biogenic emissions from northwestern South Asia. Comparison with other ice core records shows that intensified anthropogenic emissions have caused a widespread increase in ammonium records in the inner TP after the 1950s. Furthermore, the significant positive relationship with the December–April Arctic Oscillation (AO) suggests that enhanced westerlies during the positive AO phase transport aerosol more efficiently to the QT. As a result, the decrease in ammonium concentrations after 1990, when anthropogenic emissions were still increasing, could be attributed to the weakening of westerlies associated with the transitioning of the AO phase from positive to negative. Our results may enhance the understanding of the influence of the westerlies on the transport of atmospheric pollutants to the central TP.