A 70-yr record of oxygen-18 variability in an ice core from the Tanggula Mountains, central Tibetan Plateau

摘要

A 33 m ice core was retrieved from the Tanggula Mts, central Tibetan Plateau at 5743 m a.s.l. in August 2005. Annual average δ~(18)O values were determined for the upper 17 m depth (14.6 m w.eq.), representing the time series since the mid-1930s. Data are compared to previous results of an ice core from Mt. Geladaindong, 100 km to the northwest, for the period 1935-2003. During the time 1935-1960, δ~(18)O values differed by 2-3‰ between the two ice cores, with generally lower ratios preserved in the Tanggula 2005 core. Differences in interannual variability and overall average ratios between the two study locations highlight the spatially variable climate controls on ice core isotope ratios within the boundary of monsoon- and westerly-impacted regions of the central Tibetan Plateau. Average annual net accumulation was 261 mm w.eq. for the period 1935-2004. The overall average δ~(18)O value was - 13.2%e and exhibited a statistically significant increase from the 1935-1969 average (-13.7‰) to the 1970-2004 average (-12.6‰). Despite the observed increase in isotope ratios, isotopic temperature dependence was not evident, based on comparison with long-term data from meteorological stations to the north and southwest of the study location. Lack of correlation between average δ~(18)O values and temperature is likely due to monsoon influence, which results in relatively greater isotopic depletion of moisture during the warm season. Evidence of monsoon impacts on precipitation in the central Tibetan Plateau has been previously documented, and statistically significant negative correlation (r=-0.37, p <0.01) between the annual average ice core δ~(18)O values and North India monsoon rainfall was observed for the period 1935-2004. Although the δ~(18)O datarnagree well with the monsoon rainfall amount, no significant correlation was observed between the core accumulation and the monsoon rainfall amount. Previous model and observational results suggest monsoon impact on δ~(18)O in precipitation may extend beyond the immediate extent of heavy monsoon rainfall, reaching the central Tibetan Plateau. These results provide evidence that the δ~(18)O variability at this study location may be sensitive to southern monsoon intensity.