Modelling tree-ring cellulose δ18O variations of two temperature-sensitive tree species from North and South America

Aliénor Lavergne, Fabio Gennaretti, Camille Risi, Valérie Daux, Etienne Boucher, Martine M. Savard, Maud Naulier, Ricardo Villalba, Christian Bégin, Joël Guiot
2017 Climate of the Past Discussions  
Oxygen isotopes in tree-rings (δ<sup>18</sup>O<sub>TR</sub>) are widely used to reconstruct past climates. However, the complexity of climatic and biological processes controlling isotopic fractionation is not yet fully understood. Here, we use the MAIDENiso model to decipher the variability of δ<sup>18</sup>O<sub>TR</sub> of two temperature-sensitive species of relevant paleoclimatological interest (<i>Picea mariana</i> and <i>Nothofagus pumilio</i>) and growing at cold high-latitudes in North
more » ... -latitudes in North and South America. In this first modelling study on δ<sup>18</sup>O<sub>TR</sub> values in both northeastern Canada (53.86°&amp;thinsp;N) and western Argentina (41.10°&amp;thinsp;S), we specifically aim at: (1) evaluating the predictive skill of MAIDENiso to simulate δ<sup>18</sup>O<sub>TR</sub> values, (2) identifying the physical processes controlling δ<sup>18</sup>O<sub>TR</sub> by mechanistic modelling and, (3) defining the origin of the temperature signal recorded in the two species. Although the linear regression models used here to predict daily δ<sup>18</sup>O of precipitation (δ<sup>18</sup>O<sub>P</sub>) may need to be improved in the future, the resulting daily δ<sup>18</sup>O<sub>P</sub> values adequately reproduce observed (from weather stations) and simulated (by global circulation model) δ<sup>18</sup>O<sub>P</sub> series. The δ<sup>18</sup>O<sub>TR</sub> values of the two species are correctly simulated using the δ<sup>18</sup>O<sub>P</sub> estimation as MAIDENiso input, although some offset in mean δ<sup>18</sup>O<sub>TR</sub> levels is observed for the South American site. For both species, the variability of δ<sup>18</sup>O<sub>TR</sub> series is more likely linked to the effect of temperature on isotopic enrichment of the leaf water rather than on the isotopic composition of the source water. We show that MAIDENiso is a powerful tool for investigating isotopic fractionation processes but that the lack of a denser isotope-enabled monitoring network recording oxygen fractionation in the soil-vegetation-atmosphere compartments limits our capacity to decipher the processes at play. This study proves that the eco-physiological modelling of δ<sup>18</sup>O<sub>TR</sub> values is necessary to interpret the recorded climate signal more reliably.
doi:10.5194/cp-2017-93 fatcat:qpby7p2fzbd7zcftdjn4a3lgti