18O16Ostandard

The 18O16O standard, also known as VSMOW (Vienna Standard Mean Ocean Water), is a reference material used for isotopic analysis of water. Specifically, it refers to the ratio of oxygen-18 (18O) to oxygen-16 (16O) isotopes within a sample of water. This ratio is a critical parameter in various scientific fields.

VSMOW was established to provide a consistent and reproducible baseline for measuring variations in the isotopic composition of natural waters. These variations are primarily driven by physical processes like evaporation and precipitation, which fractionate isotopes differently. For instance, lighter isotopes like 16O tend to evaporate more readily, leaving behind water with a slightly enriched 18O/16O ratio.

The 18O/16O ratio in VSMOW is defined as exactly 0.0020052. All other water samples are then compared to this standard, and their isotopic composition is expressed as a delta value (δ) in per mil (‰). A positive delta value indicates that the sample is enriched in 18O relative to VSMOW, while a negative delta value signifies depletion. This allows scientists to accurately track water sources, study past climate conditions, understand hydrological cycles, and investigate various environmental processes.