Dendro-isotopy (δ¹⁸O) of the framework of Notre-Dame de Paris : Impact of carbonization and reconstruction of the Medieval Climate Anomaly in the Paris Basin ; Dendro-isotopie (δ¹⁸O) de la charpente de Notre-Dame de Paris : Impact de la carbonisation et reconstruction de l'Anomalie Climatique Médiévale dans le Bassin Parisien

The 800-year-old Notre-Dame de Paris Cathedral (NDP) was severely damaged by a fire on April 15 of 2019. While the charred timbers from its framework are no longer reusable, they have become valuable resources for researchers. These woods hold important insights into the Middle Ages, particularly the Medieval Climate Anomaly (MCA, 10th-13th centuries), once thought to be a uniformly warm period. However, the climate during this period was neither consistent over time nor uniform across regions. To gain a more accurate understanding, it is essential to focus on areas that are underrepresented in current climate syntheses, such as temperate, low-altitude regions. This thesis aims to carry out such a climatic reconstruction in the Paris Basin (BP) during the MCA, by analysing the oxygen isotopic composition (δ¹⁸O) of cellulose in medieval tree rings from the timbers of Notre Dame Cathedral in Paris (NDP) and other contemporary monuments. Carbonization experiments were carried out to assess changes in the δ¹⁸O of oak wood during fire events, like the one that affected NDP. The results showed a significant decrease in δ¹⁸O (up to -30 ‰ at 900°C) during the thermal degradation of wood compounds. Additionally, our research demonstrated that the variability in measurements between replicas (up to 3.6 ‰ at 600°C) prevents δ¹⁸O from being a reliable proxy for climate reconstructions. However, preliminary results show that residual cellulose retains its original isotopic signal at heating temperatures below 300°C. A dataset of 34 oak timbers from various medieval buildings in the Paris Basin, spanning part of the Medieval Climate Anomaly (1046-1240 AD), has provided a regional climatic history divided into two distinct phases, centered around 1129. The first phase is marked by cool, wet summers, challenging the traditional view of the MCA as uniformly warm and favourable period. The second phase shows a gradual transition toward warmer, drier summers, with extreme heat events in the early 13th century punctuating this ...