Examination of the parameters controlling the triple oxygen isotope composition of grass leaf water and phytoliths at a Mediterranean site: a model–data approach

Abstract. Triple oxygen isotopes (17O-excess) of water are useful to trace evaporation at the soil–plant–atmosphere interface. The 17O-excess plant silica, i.e., phytoliths, inherited from leaf water, was previously calibrated in growth chambers as a proxy atmospheric relative humidity (RH). Here, using model–data approach, we examine parameters that control triple isotope composition bulk grass and phytoliths natura, O3HP experimental platform located French Mediterranean area. A plot equipped measure for 1 year, all environmental physiological relevant modeling water. In particular, hydrogen vapor above measured continuously cavity ring-down spectrometer, temperature monitored scale an infrared (IR) radiometer. Grass leaves were collected different seasons year over 24 h period June. extracted by cryogenic vacuum distillation analyzed ratio mass spectrometry (IRMS). Phytoliths IR–laser fluorination–IRMS after chemical extraction. We showed traditional Craig–Gordon steady-state model modified reliably predicts during daytime but is sensitive uncertainties on leaf-to-air difference. Deviations steady state night well represented system predictable non-steady-state model. confirms applicability 17O-excessphyto vs. RH equation established previous chamber experiments. Further, it recorded average rather than daily RH, related low transpiration silicification night. This approach highlights utility improve understanding exchange natura experiment underlines proxy.