Continental-scale patterns in modern wood cellulose δ18O: Implications for interpreting paleo-wood cellulose δ18O

Abstract The isotopic composition of ancient wood may be a useful archive of some climatic or geochemical conditions of the past, but presently there are many uncertainties that constrain such interpretations. We sampled naturally growing, predominantly native trees in forested regions of North America and the Caribbean to evaluate the strength of the relationships among cellulose δ 18 O (δ 18 O cel ), relative humidity (RH), precipitation δ 18 O (δ 18 O ppt ), and mean annual temperature (MAT) at the continental scale, and the general range of variability in δ 18 O cel associated with site hydrologic conditions and species differences. We found up to 4‰ differences among different species growing at the same site, that conifer cellulose at a site is more enriched than angiosperm cellulose by 1.5‰ ( p 18 O cel . At the continental scale, δ 18 O cel was strongly influenced by modeled δ 18 O ppt ( R 2  = 0.80, p min ) combined with δ 18 O ppt explained more of the variability ( R 2  = 0.93, p 18 O cel across North American and Caribbean forests. MAT and δ 18 O cel were also strongly correlated across North America ( R  = 0.91 and 0.95, p 18 O ppt and δ 18 O cel is not constant (varying from 35–44‰) and is inversely correlated with δ 18 O ppt . The relationships among δ 18 O ppt , RH min , δ 18 O cel , and MAT established for North America and the Caribbean applied reasonably well when δ 18 O cel was used to estimate MAT and δ 18 O ppt in Asia, Europe, and South America, but there were important exceptions. The most accurate predictions of MAT and δ 18 O ppt from δ 18 O cel require RH min . Predictions of δ 18 O ppt and MAT made from δ 18 O cel alone produced errors of up to 8‰ and 16 °C, respectively.