Penchenat T., Vimeux Françoise, Daux V., CattaniO., Viale M., Villalba R., Srur A., Outrequin C. (2020). Isotopic equilibrium between precipitation and water vapor in northern Patagonia and its consequences on delta 18O cellulose estimate. Journal of Geophysical Research : Biogeosciences, 125 (3), e2019JG005418 [18 p.]. ISSN 2169-8953.
Titre du document
Isotopic equilibrium between precipitation and water vapor in northern Patagonia and its consequences on delta 18O cellulose estimate
Penchenat T., Vimeux Françoise, Daux V., CattaniO., Viale M., Villalba R., Srur A., Outrequin C.
Source
Journal of Geophysical Research : Biogeosciences, 2020,
125 (3), e2019JG005418 [18 p.] ISSN 2169-8953
Modeling work of the isotopic composition of tree ring cellulose (delta 18O cell) relies on the isotopic equilibrium assumption between atmospheric water vapor and tree source water, frequently assimilated to integrated precipitation. Here, we explore the veracity of this assumption based on observations collected during a field campaign in Río Negro province (Argentina) in February-March 2017. We examine how the observed isotopic composition of water vapor deviates from equilibrium with precipitation. This deviation, named isotopic disequilibrium (delta 18Ovap_eq), is low (between-2.0/00and 4.1/00) and a significant relationship is observed between the isotopic composition of water vapor and its expected value at equilibrium. Negative delta 18O vap_eq can be explained by evaporation of small raindrops (from 1% to 5% ofinitial droplet mass). Positive delta18O vap_eq can result from vegetation transpiration with transpired water accounting for 14% to 29% to ambient water vapor. The low delta18O vap_eq at the study site may be due to the high level of relative humidity (from 70% to 96%) favoring isotopic diffusive exchanges between the two water phases and thus promoting the isotopic equilibrium. We examine the impact of the isotopic equilibrium assumption on the calculation of delta 18O cell. A perfect agreement is shown between observed and calculated delta18O cell provided that the isotopic composition of source water is significantly higher than the expected averaged isotopic composition of precipitation over the tree growing period.
Plan de classement
Analyse, évolution des climats [021CLIMAT01]
;
Climatologie / Météorologie [032CLIMET]
;
Etude du bilan d'énergie des surfaces naturelles ou cultivées / mesure des flux de chaleur et de vapeur d'eau [072BCLIGE02]
