Tree ring oxygen isotope in Asia

Abstract

Tree-ring oxygen isotope (δ18OTR) is a powerful proxy for paleoclimatology, ecology and archaeology, δ18OTR studies in Asia over the past ∼50 years have made significant achievements in improving our understanding of Asian climatic and ecological systems. Here, we review these developments in δ18OTR research in Asia. Most study sites are located within East Asia, Southeast Asia, South Asia, and North Asia, and δ18OTR records from conifers, broadleaf trees, and shrubs have been produced. Progress has been made in the following areas: (1) Experimental techniques. The novel plate method for cellulose extraction has been developed, which reduces experimental time and greatly improves efficiency. (2) Development of δ18OTR chronologies. Ninety-six chronologies exceeding 200 years in length have been produced. A 4354-year δ18OTR chronology with an annual-resolution has been produced in Japan, and a 6700-year δ18OTR chronology with a 1–5 year resolution has been produced in the northeastern Tibetan Plateau, which is the longest in Asia. (3) Biological influences on δ18OTR. Variations of intra- and inter-tree and inter-species δ18OTR have been investigated, and the relationship between tree age and δ18OTR has been explored. (4) Climatic implications. Seasonal δ18OTR records primarily reflect the variability of precipitation δ18O, facilitating high-resolution paleoclimate reconstructions, while interannual δ18OTR records mainly reflect summer moisture variability. (5) Climate reconstructions. Quantitative estimates have been produced for past precipitation, relative humidity, PDSI (Palmer Drought Severity Index), runoff, and other parameters from δ18OTR records. Since 1850, δ18OTR chronologies in monsoon regions show upward trends indicative of drying, while these from westerlies regions exhibit downward shifts implying wetting. (6) Dating. Intra- and inter-annual δ18OTR records help determine the annual growth of trees without rings and facilitate the cross-dating of trees with rings. Thus, the dating of archaeological and buried wood is feasible via comparisons with δ18OTR master chronologies. Promising areas of development include climatic implications (e.g., Position-specific isotope analysis, seasonal δ18OTR records on longer timescales and larger spatial scales), climate reconstructions (syntheses of multiple sites and records, development of long chronologies, deep time paleoclimate reconstructions) and ecological applications (e.g., the response of trees to climatic extremes, and the combinations with multiple tree-ring multiple proxies such as width and density).