Southern Tibetan Plateau ice core δ18O reflects abrupt shifts in atmospheric circulation in the late 1970s
Ice cores from the Tibetan Plateau provide high-resolution records of changes in the snow and ice isotopic composition. In the monsoon sector of southern Tibetan Plateau, their climatic interpretation has been controversial. Here, we present a new high-resolution δ18O record obtained from 2206 measurements performed at 2-3 cm depth resolution along a 55.1 m depth ice core retrieved from the Noijinkansang glacier (NK, 5950 m a.s.l.) that spans the period from 1864 to 2006 AD. The data are characterized by high δ18O values in the nineteenth century, 1910s and 1960s, followed by a drop in the late 1970s and a recent increasing trend. The comparison with regional meteorological data and with a simulation performed with the LMDZiso general circulation model leads to the attribution of the abrupt shift in the late 1970s predominantly to changes in regional atmospheric circulation, together with the impact of atmospheric temperature change. Correlation analyses suggest that the large-scale modes of variability (PDO and ENSO, i.e. Pacific Decadal Oscillation and El Nino-Southern Oscillation) play important roles in modulating NK δ18O changes. The NK δ18O minimum at the end of the 1970s coincides with a PDO phase shift, an inflexion point of the zonal index (representing the overall intensity of the surface westerly anomalies over middle latitudes) as well as ENSO, implying interdecadal modulation of the influence of the PDO/ENSO on the Indian monsoon on southern TP precipitation δ18O. While convective activity above North India controls the intra-seasonal variability of precipitation δ18O in southern TP, other processes associated with changes in large-scale atmospheric circulation act at the inter-annual scale.