Abstract
Abstract. 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 δ18O 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, δ18O 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 δ18O value was −13.2‰ 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 δ18O 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 δ18O values and North India monsoon rainfall was observed for the period 1935–2004. Although the δ18O data agree 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 δ18O in precipitation may extend beyond the immediate extent of heavy monsoon rainfall, reaching the central Tibetan Plateau. These results provide evidence that the δ18O variability at this study location may be sensitive to southern monsoon intensity.
Highlights
High elevation ice cores from the mid- and low-latitude regions have been instrumental for reconstructing environmental records
Similar results reported for an ice core from Svalbard were explained by a large standard deviation in accumulation rates that can mask the annual signal in frequency space (Pohjola et al, 2002)
Vuille et al (2008) suggested that effects of monsoon moisture on isotope ratios may be observed in areas where local precipitation is not directly affected by monsoon variability, due to increased rainout and distillation processes during transport. These results provide some assessment of monsoon impact on the isotope ratios in this ice core, the basis of the observed relationship between North India precipitation and δ18O values ratios at this study location remains unclear
Summary
High elevation ice cores from the mid- and low-latitude regions have been instrumental for reconstructing environmental records. With sufficiently high elevation to preserve annual accumulation, the mountain regions of the Tibetan Plateau (TP) provide an ideal location to examine interannual variability of geochemical signals preserved in snow and ice. Stable isotopes in ice cores have been widely used as a paleothermometer in this region. Moisture sources and water vapor recycling differ between the northern and southern TP (Tian et al, 2001a), resulting in spatially and temporally variable isotope-temperature relationships. Isotopic dependence on temperature is established for continental locations in the northern TP, far-removed from monsoon moisture (Yao et al, 1996). In those areas, the most depleted isotope ratios are associated with accumulation during the coldest temperatures and the least depleted ratios arrive with warm-season
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