Search

Stable isotopes in tree rings are increasingly used as proxies for climatic and ecophysiological changes. However, uncertainties remain about the strength and consistency of their response to environmental variation at different temporal (i.e. seasonal to inter-decadal) scales., We developed 5 yr of intra-seasonal and 62 yr of early- and late-wood δ13C and δ18O series of Smith fir ( Abies georgei var. smithii) on the southeastern Tibetan Plateau, and used a process-based forward model to examine the relative importance of environmental and physiological controls on the isotopic data., In this temperate high-altitude region, the response, both δ18O and δ13C, is primarily to variations in relative humidity, but by different processes. In δ18O, the response is via source water δ18O but also arises from leaf water 18O enrichment. In δ13C, the response is via changes in stomatal conductance but is modified by carry-over effects from prior periods., We conclude that tree-ring δ18O may be a more robust climate proxy than δ13C, and δ13C may be more suited to studies of site-related physiological responses to the local environment. [ABSTRACT FROM AUTHOR]

To reveal the influence of current warming on tree growth and δ18O in a sensitive high-latitude region that is undergoing rapid climate change, we examined tree width and the earlywood and latewood δ18O at two sites with a 400-m elevation difference in the Sygera Mountains of the southeastern Tibetan Plateau. The study period was from 1950 to 2011. The mean tree-ring index at the low site was higher than that at the high site during the study period. The climatic responses of earlywood and latewood δ18O at both sites were similar. Earlywood δ18O was mainly influenced by the June to August temperature and total cloud cover, whereas latewood δ18O was mainly controlled by relative humidity from July to August. Spatial correlations with CRU TS 3.1 regional data suggest that our δ18O chronologies can represent climatic changes over large regions. The high offset between earlywood δ18O at the two sites (2.3‰ higher at the low site) was mainly influenced by the high temperature lapse rate as a function of altitude during the earlywood growing season. Furthermore, meltwater with lower δ18O values might have affected earlywood δ18O at the high site, and thereby increased the earlywood δ18O offset between two sites. The low latewood δ18O offset between the two sites (0.4‰ higher at the low site) was not significant, but appears to have been primarily influenced by the low precipitation δ18O lapse rate as a function of altitude during the latewood growing season. Earlywood δ18O of Smith fir suitable for reconstructing past temperatures and latewood δ18O suitable for reconstructing past relative humidity on the southeastern Tibetan Plateau were identified. [ABSTRACT FROM AUTHOR]

ABSTRACT We developed an annual tree-ring δ18O chronology from Larix sibirica in the eastern Tianshan Mountains of northwestern China. Climatic response revealed that tree-ring δ18O was significantly positively correlated with the mean and maximum July-August temperatures, whereas the July precipitation and relative humidity were significantly negatively correlated with tree-ring δ18O. The self-calibrating Palmer drought severity index (sc_PDSI) in July-August was significantly correlated with the tree-ring δ18O, which reflects the comprehensive effects of the three parameters on tree-ring δ18O fractionation. We established a robust reconstruction of July-August sc_ PDSI that accounted for 38.4% of the total variance of sc_PDSI from 1959 to 2008. The sc_PDSI reconstruction yields new insights on past drought that were not previously realized in other PDSI reconstructions (e.g. Monsoon Asia Drought Atlas) from the region. The reconstruction revealed several wet and dry periods but no trend towards a wetter climate in the eastern Tianshan Mountains during the last two decades. It also detected synergistic effects of the North Atlantic Oscillation and the El Niño-Southern Oscillation on regional moisture conditions as a result of teleconnections between tropical oceans and mid-latitude circulation patterns. [ABSTRACT FROM AUTHOR]