High resolution climate reconstruction for the last millennium using tree rings
Zusammenfassung der Projektergebnisse
Present-day conditions and calibration. Tree ring stable isotope records have been established for the 20th century from 4 teak trees provided by Indian partner (IITM) from the Kerala region, S-India. This region was selected for assessing the recently observed weakening of the Walker circulation by thorough comparison of tree ring stable isotope records from the Indonesian warm pool. Statistical analysis has revealed that the number of replication at the Kerala tree site is not sufficient for an appropriate expressed population signal, however, new tree material from India could not be sampled and processed during the term of the project. Hence, tree ring stable isotope work and dendroclimatic calibration has been focused on Investigations from the Indonesian warm pool. Palaeoclimate reconstruction. Novel methodologies have been setup and applied allowing for serial sectioning of ultra-narrow (down to 10µm) tree rings for stable isotope analysis. This has enabled intra- and interannual isotope analyses of tree rings from very old, slow growing trees from Himalayan timberline sites, e.g. junipers with distinct hazel-growth ring structures. Tree ring stable isotope analysis for the W-Himalayan sites (Kashmir) have been performed by the Indian partner IITM. A centennial isotope record was established for individual trees of a site in S-India (Kerala). Statistical analysis has been performed revealing that the number of trees provided by Indian partner (IITM) from the Kerala region, S-India is not sufficient for an appropriate expressed population signal (EPS) of 85%, allowing for high quality climate reconstructions. The Kerala region was particularly selected for assessing the recently observed weakening of the Walker circulation by thorough comparison of tree ring stable isotope records from the Indonesian warm pool. Since additional tree material from India could not be obtained and processed during the term of the project, tree ring stable isotope work, dendroclimatic calibration and reconstruction focused on investigations from the Indonesian warm pool. Finally, in this project the first well replicated, centennial multi-parameter record (ring width, stable isotopes) from tropical Teak was established. Individual tree-ring parameters were found sensitive to rainfall of different time intervals of the seasonal monsoon pattern. Tree-ring δ18O responds to peak dry season and prime rainy season rainfall with correlations opposite in sign. High-resolution intra-annual tree-ring δ18O proved to be very useful tool to disentangle dry and rainy season rainfall signals.
