How will your lab test these isotopic ratios?
Either oxygen or deuterium isotopes can be analyzed to find temperature data from an ice core, but oxygen isotopes are generally more common. To find ¹⁸O/¹⁶O ratios, you cut away a sample from the ice core at a certain depth. You then melt down the sample at room temperature and place the resulting water in a vial. You add pure carbon dioxide with a known isotopic ratio to the vial, which you then maintain at 40°C for five hours. This allows oxygen-18 isotopes to transfer from the water to the carbon dioxide in a process called equilibration, as illustrated in the following equation.

Following equilibration, the ¹⁸O isotopes have been transferred from the water to carbon dioxide, giving CO₂ the original isotopic ratio of the water from the ice core. Finally, you can run the CO₂ through a mass spectrometer and determine the ¹⁸O/¹⁶O ratio of the sample from the ratio of the intensities of peaks 44 and 46. An equation can then be used to relate this to the original atmospheric temperature at the time that the ice formed. These equations vary depending on location, as the relationship between isotopic abundance and temperature is slightly different in each climate.