Variations of 17O/16O and 18O/16O in meteoric waters

The variations of delta O-17 and delta O-18 in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle. In order to close significant information gaps in the present distribution of delta O-17 and delta O-18 of meteoric water, we have run precise measurements, with respect to VSMOW, on samples distributed globally from low to high latitudes. Based on the new and existing data, we present the Global Meteoric Water Line (GMWL) for delta O-17 and delta O-18 as: In(delta O-17 + 1) = 0.528 In(delta O-18 + 1) + 0.000033 (R-2 = 0.99999) In addition to meteoric water, we carried out the first measurements of seawater from the Pacific and Atlantic oceans with respect to VSMOW. The obtained results show that the slope of the trend line In(delta O-17 + 1) vs. In(delta O-18 + 1) of seawater samples is 0.528, the same as for meteoric water, but the regression intercept is -5 per meg. Thus, the positive intercept in the GMWL indicates an excess of O-17 in meteoric waters with respect to the ocean. An excess (or depletion) of O-17 in water is defined as: O-17-excess = In(delta O-17 + 1) - 0.528(delta O-18 + 1) Most meteoric water samples have positive O-17-excess of varying magnitudes with an average of 37 per meg with respect to VSMOW. We explain how these positive values originate from evaporation of sea water into marine air, which is undersaturated in water vapor, and how subsequent increase of O-17-excess occurs when atmospheric vapor condenses to form liquid and solid precipitation. We also clarify the effect of excessive evaporation on O-17-excess. Finally, based on the new results on O-17-excess of seawater we recalculated the relationship of delta O-17 vs. delta O-18 in vapor diffusion in air as (18)alpha(diff) = 1.0096. (C) 2010 Elsevier Ltd. All rights reserved.