PRELIMINARY-RESULTS OF A TIBETAN STABLE C-ISOTOPE CHRONOLOGY DATING FROM 1200 TO 1994

Recently the set up of a stable carbon isotope chronology of juniper t ree rings of the eastern Tibet timberline has been initiated. First re sults for the last 800 years will be presented. The dominant delta(13) C pattern shows higher values between 1200 and 1450. Thereafter, a dec rease is observed until a minimum is reached at about 1650. Low values are observed until 1750. From then onwards the delta(13)C values incr ease again, followed by a sharp decline since around 1900. Local histo rical, glaciological, dendrochronological and icecore data suggest tha t the isotope values mirror a climatic signal between 1200 and 1900. T he negative trend in the 20th century can probably be attributed to sp ecies specific physiological reactions induced by the anthropogeniocal ly elevated CO2 concentration. Since the tree rings of some time perio ds are extremely narrow, always 5 tree rings had to be combined. Becau se of this sampling procedure (pentad sequences) at present the 50 yea rs of instrumentally measured meterological data could not be correlat ed to the corresponding delta(13)C record.