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.) 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.
Highlights
The Tibetan Plateau (TP) is a unique area where the topography plays a key role in the regional atmospheric circulation and the hydrological cycle, which encompasses the largest number of glaciers outside of polar regions (Yao et al 2012)
We have investigated whether similar anomalous low δ18O values are recorded in other Tibetan ice cores
We have reported the δ18O signal recorded by a new Southern Tibetan ice core
Summary
The Tibetan Plateau (TP) is a unique area where the topography plays a key role in the regional atmospheric circulation and the hydrological cycle, which encompasses the largest number of glaciers outside of polar regions (Yao et al 2012). Ice cores provide high-resolution proxy records of climate variability, archived through e.g. changes in water stable isotopes (usually expressed in a delta notation, such as δ18O used hereafter). Precipitation δ18O from these stations displays a clear seasonal cycle, typical of southern TP, with maximum values in spring and minimum values in summer (Fig. 1b, Gao et al 2009, 2013; Yao et al 2013) This seasonal pattern is identified in the NK ice core and provides the basis for its age scale The European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis results (Uppala et al 2005) are used to nudge the horizontal wind fields with a relaxation time of 1 h This warrants that the large-scale LMDZiso simulated wind fields are consistent with the observations, and allows to use of the LMDZiso framework to understand and quantify the role of changes in atmospheric circulation in the observed δ18O variability. A zoomed simulation using the zoom functionality of the LMDZ model, stretching the grid to the horizontal resolution of 50–60 km between 0° and 55°N and 60° and 130°E, are used here to detect the inter-annual variability
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