Climatological significance of δ18O in north Tibetan ice cores

Abstract

Oxygen isotopic ratios (δ 18 O) of precipitation samples collected over several years at three meteorological stations on the northern Tibetan Plateau were used to conduct the first investigation of the relationship between δ 18 O and contemporaneous air temperatures (T a). Inferring past temperatures from δ 18 O measured in recently acquired Tibetan ice cores necessitates establishing whether a δ 18 O‐T a relationship exists. For each station a strong temporal relationship is found between δ 18 O and T a, particularly for monthly averages which remove synoptic‐scale influences such as changes in condensation level, condensation temperature, and moisture sources. Moisture source is identified as a major factor in the spatial distribution of δ 18 O, but air temperature determines the temporal fluctuations of δ 18 O at individual sites on the northern Tibetan Plateau. The 30‐year records of annually averaged δ 18 O from three different ice coring sites are not correlated significantly with contemporaneous air temperature records from their closest meteorological station (150 to 200 km). However, since 1960 the three air temperature records reveal a modest warming trend, while the three contemporaneous δ 18 O records show a modest 18 O enrichment.