Oxygen isotopic ratios in the dating of ice cores
Oxygen isotope ratio cycles are cyclical variations in the ratio of the abundance of oxygen with an atomic mass of 18 to the abundance of oxygen with an atomic mass of 16 present in some substances, such as polar ice or calcite in ocean core samples, measured with the isotope fractionation.
The ratio is linked to water temperature of ancient oceans, which in turn reflects ancient climates.
Drilling a vertical hole through this ice involves a serious effort involving many scientists and technicians, and usually involves a static field camp for a prolonged period of time.
All of these isotopes are termed 'stable' because they do not undergo radioactive decay.
Robert Mulvaney, a glaciologist with the British Antarctic Survey, explains.
The cornerstone of the success achieved by ice core scientists reconstructing climate change over many thousands of years is the ability to measure past changes in both atmospheric greenhouse gas concentrations and temperature.
Using sensitive mass spectrometers, researchers are able to measure the ratio of the isotopes of both oxygen and hydrogen in samples taken from ice cores, and compare the result with the isotopic ratio of an average ocean water standard known as SMOW (Standard Mean Ocean Water).
The water molecules in ice cores are always depleted in the heavier isotopes (that is, the isotopes with the larger number of neutrons) and the difference compared to the standard is expressed as either O and D during cold periods than there is in warm. Simply put, it takes more energy to evaporate the water molecules containing a heavy isotope from the surface of the ocean, and, as the moist air is transported polewards and cools, the water molecules containing heavier isotopes are preferentially lost in precipitation.
They allow us to go back in time and to sample accumulation, air temperature and air chemistry from another time.