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Accueil du site → Doctorat → Allemagne → 2020 → Stable isotope variations in tree rings as indicators of environmental change and paleohydroclimate variability in north Iran

Friedrich-Alexander-Universität Erlangen-Nürnberg (2020)

Stable isotope variations in tree rings as indicators of environmental change and paleohydroclimate variability in north Iran

Foroozan Zeynab

Titre : Stable isotope variations in tree rings as indicators of environmental change and paleohydroclimate variability in north Iran

Stabile Isotopenvariationen in Baumringen als Indikatoren für Umweltveränderungen und Paläohydroklimatische Variabilität im Nord-Iran

Auteur : Foroozan Zeynab

Université de soutenance : Friedrich-Alexander-Universität Erlangen-Nürnberg

Grade : Doktorgrades Dr. rer. nat. 2020

Résumé partiel
Precise knowledge about the long-term hydroclimatic variability is essential to analyze the impact of natural and anthropogenically induced climate change, especially in the world’s arid to semi-arid regions. Iran is located in one of the world’s most water-scarce and dry areas in Southwestern Asia. Hence, the country is highly subjected to water scarcity, water-related natural hazards such as drought and flash flood, and thus prone to their consequences on the ecosystem and human society. Besides, the growing population and the thirst for socio-economic development, in turn, increase the region’s vulnerability to climate change. However, the current solutions to the aggravating water crisis are inadequate and inefficient without a clear picture of regional water availability in the future. In this context, a major defect is the lack of hydroclimate (precipitation) data of the past and present. A neglected area in this regard is the high potential of natural climate archives for extending our knowledge about past and present variations in hydroclimate. This research was thus initiated to explore the potential of a natural climate proxy for paleoclimate reconstructions to improve our understanding of long-term regional climate variability in Iran. Accordingly, we evaluated the potential of stable isotopes in tree-ring cellulose to serve as paleoclimate indicators. We determined the climate signal recorded in δ13C and δ18O variations in tree-ring cellulose. Besides, this study tested the ecological responses of two tree species belonging to different plant functional types, an evergreen conifer (Juniperus polycarpos) and a broadleaved deciduous oak (Quercus macranthera), growing under distinct climate conditions to their environments, to increased CO2, and recent climate change by analyzing trends of intrinsic water-use efficiency (iWUE). In this thesis, we evaluated species-specific responses to drought of those tree species to provide baseline data for possible forest management efforts alleviating the impacts of expected climate change. The observed increasing trends in iWUE indicated reduced stomatal conductance in both study species in response to the changing climate and elevated atmospheric CO2. The mean correlations among individual δ13C series in each site and between the site δ13C chronologies provide strong evidence of a robust common climate signal in isotope series. The proxy-climate analysis revealed that the interplay between the combined influence of climate and local site conditions and species behavior determines δ13C variations in both species. The results showed that drought stress, which is controlled by precipitation, is the dominant climatic control on the δ13C fluctuations in both oak and juniper trees. In general, juniper responded more sensitive to moisture stress and is thus a more suitable proxy for paleohydroclimatic studies in northern Iran.

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