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Oxygen isotopes in tree rings (delta O-18(TR)) 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 in delta O-18(TR) of two temperature-sensitive species of relevant palaeoclimatological interest (Picea mariana and Nothofagus pumilio) and growing at cold high latitudes in North and South America. In this first modelling study on delta O-18(TR) values in both northeastern Canada (53.86 degrees N) and western Argentina (41.10 degrees S), we specifically aim at (1) evaluating the predictive skill of MAIDENiso to simulate delta O-18(TR) values, (2) identifying the physical processes controlling delta O-18(TR) 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 delta O-18(TR) of precipitation (delta O-18(P)) may need to be improved in the future, the resulting daily delta O-18(P) values adequately reproduce observed (from weather stations) and simulated (by global circulation model) delta O-18(P) series. The delta O-18(TR) values of the two species are correctly simulated using the delta O-18(P) estimation as MAIDENiso input, although some offset in mean delta O-18(TR) levels is observed for the South American site. For both species, the variability in delta O-18(TR) series is primarily linked to the effect of temperature on isotopic enrichment of the leaf 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 delta O-18(TR) values is necessary to interpret the recorded climate signal more reliably

climate of the past

Modelling tree ring cellulose &amp;lt;i&amp;gt;δ&amp;lt;/i&amp;gt;&amp;lt;sup&amp;gt;18&amp;lt;/sup&amp;gt;O variations in two temperature-sensitive tree species from North and South America