Tree-ring delta D as an indicator of Asian monsoon intensity

Oxygen and hydrogen isotopic compositions of meteoric water are known to co rrelate with surface air temperature, except in tropical areas. This relati onship has been described using a number of terms corresponding to specific observations, such as latitude, altitude and seasonal effects. However, th ese temperature effects do not seem to apply to precipitation in monsoonal areas of Asia. Questions have been raised as to whether the isotopic compos ition of meteoric water can be used to reconstruct paleomonsoon intensity. Tree rings of two modern spruce trees (Picea meyeri) and a 10,000-yr-old ti mber (Picea jezoensis) were analyzed for hydrogen isotopic composition. On average, the older tree is depleted in deuterium by 45 parts per thousand c ompared to the modern trees. We attribute this isotopic depletion to the st rength of summer monsoons, which were more intense in the early Holocene th an at present. Although this study is not definitive, it suggests that pale omonsoon intensity can be reconstructed by direct or proxy methods that yie ld the oxygen or hydrogen isotopic composition of meteoric water, (C) 1999 University of Washington.