A Simple Framework to Evaluate the Interactions between Evaporation and Shallow Mixing in the Marine Boundary Layer from Water Isotopic Measurements

We propose a framework to analyze the isotopic variations of water vapour in the Marine Boundary Layer (MBL) which aim at reproducing the influence of the evaporative flux, via equilibrium and kinetic fractionation processes. The framework consists of coupling the Craig and Gordon equation with a mixing model that allows to mix the evaporative flux with a dry term characteristic of free tropospheric or laterally advected air. Analyses in the different isotopic spaces (dD-q, d18O-q, d-excess-q and combined) allows to easily distinguish the moistening by surface evaporation and the drying by shallow convection. Using long-term surface isotopic records at Bermuda and in Iceland, the suitability of the model is demonstrated.