1 Ice and Climate, The Niels Bohr Institute, Faculty of Science, Københavns Universitet2 Astrophysics and Planetary Science, The Niels Bohr Institute, Faculty of Science, Københavns Universitet3 Ice and Climate, The Niels Bohr Institute, Faculty of Science, Københavns Universitet4 Astrophysics and Planetary Science, The Niels Bohr Institute, Faculty of Science, Københavns Universitet
Experimental investigations and implications for stable water isotope studies
RATIONALE: The equilibrium fractionation factors govern the relative change in the isotopic composition during phase transitions of water. The commonly used results, which were published more than 40 years ago, are limited to a minimum temperature of -33 degrees C. This limits the reliability in cold regions. With recent instrumental developments it is now possible to test the accuracy of the earlier results as well as extend the temperature range. METHODS: Novel measurements were made of the ice-vapor equilibrium fractionation factor between 0 degrees C and -40 degrees C, from a unique experimental setup using both a Picarro cavity ringdown spectrometer and a TC/EA IRMS system. Using both systems allows for continuous monitoring of the equilibrium state of the system as well as testing for reproducibility. RESULTS: The results of the experiments show fractionation factors for H-2 and O-18 values, with a temperature dependency in accordance with theory for equilibrium fractionation. We obtain the following expressions for the temperature dependency of the fractionation coefficients: ln(alpha(delta 2H)) = 0.2133 - 203.10/T + 48888/T-2 ln(alpha(delta 18O)) = 0.0831 - 49.192/T + 8312.5/T2 Compared with previous experimental work, a significantly larger for H-2 is obtained while, for O-18, is larger for temperatures below -20 degrees C and slightly lower for temperatures above this. CONCLUSIONS: Using the new values for alpha, a Rayleigh distillation model shows significant changes in both magnitude and shape of an annual deuterium excess signal in Greenland. This emphasizes the importance of a well-defined value of for accurate studies of the processes in the hydrological cycle and underlines the significance of the differences between the results of this work and earlier work. Copyright (c) 2013 John Wiley & Sons, Ltd.
Rapid Communications in Mass Spectrometry, 2013, Vol 27, Issue 19, p. 2149-2158