Southern Tibetan Plateau Ice Core δ18o Reflects Abrupt Shifts in Atmospheric Circulation in the Late 1970s

Abstract:

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.), and spanning the period 1864 to 2006. The data depict high δ¹⁸O levels in the 19^th century, in the 1910s, 1960s, 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 attributing of the abrupt shift in the late 1970s predominantly to changes in regional atmospheric circulation rather than to changes in local temperature. Correlation analyses suggest that the large-scale modes of variability (PDO and ENSO) 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 as well as ENSO, implying interdecadal modelation of the PDO/ENSO on the influence of 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.