Master´s thesis defense by Niels Ole Ørum – Københavns Universitet

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Master´s thesis defense by Niels Ole Ørum

Title: "Evaporation from a body of water"

Abstract: Kinetic fractionation of water isotopologues during evaporation from the ocean provides an important climate signal, potentially yielding information of the moisture sources for water trapped in ice cores. The parameters controlling kinetic fractionation are currently uncertain. This thesis specifically attempts to estimate the effect of wind speed. The availability of Cavity Ring-Down Spectroscopy(CRDS) analysers has made the measurements of isotopologues in water vapour simpler and faster than the previous method of cryotrapping, allowing for many measurements to be done in a short time. To estimate the effect of wind speed, a wind tunnel was constructed, in which dry air was blown over a basin of liquid water and the isotopic ratio of the air stream was measured as it gradually saturated. The resulting data was compared to a model based on the work of Craig and Gordon [1965] and the ratio of profile coefficients were fitted to observations and used as a measure of kinetic fractionation. Estimation of the goodness of fit resulting in the model-data comparison suggested a poor fit for all but one measurements series. This measurement series yielded the ratio: Γ (1H216O)/ Γ (HD16O) =0.9750±0.0011. This value compares well to the work of Merlivat [1978], but conflicts with that of Cappa et al. [2003]. The effect of wind speed on kinetic fractionation during evaporation was ultimately not established.

Supervisors:
Bo Møllesøe Vinther
Hans Christian Steen-Larsen

Censor:
Kerim Nisancioglu