CLIMATOLOGICAL SIGNIFICANCE OF DELTA-O-18 IN NORTH TIBETAN ICE CORES

Oxygen isotopic ratios (delta(18)O) of precipitation samples collected over several years at three meteorological stations on the northern T ibetan Plateau were used to conduct the first investigation of the rel ationship between delta(18)O and contemporaneous air temperatures (T-a ). Inferring past temperatures from delta(18)O measured in recently ac quired Tibetan ice cores necessitates establishing whether a delta(18) O-T-a relationship exists. For each station a strong temporal relation ship is found between delta(18)O and T-a, particularly for monthly ave rages which remove synoptic-scale influences such as changes in conden sation level, condensation temperature, and moisture sources. Moisture source is identified as a major factor in the spatial distribution of delta(18)O, but, air, temperature determines the temporal fluctuation s of delta(18)O at individual sites on the northern Tibetan Plateau, T he 30-year records of annually averaged delta(18)O from three differen t ice coring sites are not correlated significantly with contemporaneo us 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 delta(1 8)O records show a modest O-18 enrichment.