The isotopic composition of evaporating waters - review of the historical evolution leading up to the Craig-Gordon model.

Attempts to explain the variations in the abundance of heavy isotopic species of water throughout the hydrologic cycle solely by means of the classical equilibrium-fractionation processes could not be reconciled with measured abundances of the isotopic species in residues of "evaporation systems". Focusing on the evaporation of surface waters, the paper follows the evolution of the concepts during the 1950-ties and early 1960-ties leading up to the formulation of the Craig-Gordan Evaporation Model in 1965.

The Piracicaba River basin: isotope hydrology of a tropical river basin under anthropogenic stress.

The stable isotope content of samples of precipitation and of the river water throughout the Piracicaba basin in Brazil was measured over a two-year period. The isotope values of precipitation follow a consistent pattern of relatively depleted values of both deuterium and oxygen 18 during the rainy summers and enriched ones during the dry winters, with all values aligned slightly above the Global Meteoric Water Line. The isotopic composition of the river water throughout the basin shows a remarkable spatial coherence and much smaller scatter of data than those of the precipitation. The isotope composition of river water is close to that of the precipitation in the rainy season, however, with a consistent lower d-excess value by 1/1000-2/1000. This is attributed to evaporative water loss in the basin, in part an expression of the recycling of water due to the anthropogenic activity in the region. The more divergent values are recorded during high-water stages in the rivers. In many cases, the floods during the beginning of the rainy season are characterized by an enrichment of the heavy isotopes and lower d-excess values when compared to the precipitation, with the opposite situation later in the rainy season. This is interpreted as resulting from the watershed/riverflow interaction pattern, and it thus suggests that the isotope composition can monitor the hydrologic situation in the basin and its changes.

Making an honest measurement scale out of the oxygen isotope delta-values.

The differential measurement of the abundance of oxygen isotopes based on reference materials, such as VSMOW for the case of water, was used because the precision of the absolute mass-spectrometric determination of the abundance fell short of the differences to be measured. Since then these measurements have been much improved, so that a calibration scheme of the oxygen isotope abundance in water, carbonates, silica, phosphates, sulfates, nitrates and organic materials is suggested, based on an accredited primary standard of oxygen in air and using standard fluorination and O(2) to CO(2) conversion techniques.