Abstract
Tree-ring cellulose oxygen isotopic composition (δ18O) is controlled by several hydrological factors such as precipitation, relative humidity, and temperature. A proxy system model can reveal how these factors affect tree-ring cellulose δ18O. In this study, to identify a key control on tree-ring cellulose δ18O variations, we performed model calculation of year-to year variation of tree-ring cellulose δ18O of Javanese teak in Indonesia from 1960 to 1998. Our model results reasonably reproduce the observed δ18O values and their temporal variations (r = 0.6; p < 0.001). Moreover, the sensitivity test shows that the cellulose δ18O values are sensitive to the teak growing period. The simulation result with earlier or later shifts of the growing period captured the amplitude of observed δ18O variations over 39 years. These results indicate that the tree-ring cellulose δ18O of Javanese teak might be influenced by a subtle shift of the intra-annual growing period.
Highlights
Java Island of Indonesia, a densely populated region, often experiences droughts and floods due to strongly varying intensity of tropical monsoon precipitation
As shown in our previous study [6], tree-ring cellulose δ18O of Javanese teak is negatively correlated with precipitation and relative humidity during the rainy season
Interannual variations between model calculation and measurement showed a significant positive correlation, with a correlation coefficient of 0.61 (p < 0.001; n = 39). These results demonstrate that the model reasonably simulates the observed isotopic values of teak cellulose
Summary
Java Island of Indonesia, a densely populated region, often experiences droughts and floods due to strongly varying intensity of tropical monsoon precipitation. The tropics have been the subject of comparatively few dendroclimatological studies because collecting tree samples with annual rings is difficult. Hisamochi et al [6] measured cellulose δ18O of ten teak disks collected at four sites in Java, and verified the synchronicity of the annual time-series variations. These results of earlier studies suggest that tree-ring cellulose δ18O is a reliable proxy for hydroclimate (i.e., precipitation and relative humidity) over Java Island. A forward model of the tree-ring cellulose δ18O, a so-called a proxy system model, has already been established and can predict isotopic compositions precisely by giving the surrounding meteorological data [7,8]. We presented the calibration of a proxy system model and the detail process how teak δ18O records the environmental conditions
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