Scientific Methods

Ice Core Sampling

Greenland and Antarctica are covered with thick layers of ice. Trapped in that ice are bubbles of the ancient atmosphere. The analysis of the isotopic composition of these bubbles is the key to reconstruct the climate of the past.

Isotopes and their role in climate reconstruction

What are isotopes?
Every element of the periodic table has a distinct amount of protons in the atomic core that is unique. Hydrogen has one proton, carbon six and oxygen eight. Protons are positively charged and repel each other. The other major component of an atomic core are neutrons, that help the core to stick together. An atomic core can have different amounts of neutrons and still be the same element. That means one element can have different isotopes. Hydrogen occurs naturally with one, two and three neutrons. 99.98% of hydrogen have one neutron. Hydrogen with two neutrons is called Deuterium and makes up 0.02% of the hydrogen, while Tritium (hydrogen with three neutrons) is radioactive and decays with a half-life of around 12 years and is because of that very rare. Oxygen has three stable isotopes 16O (eight protons and eight neutrons), 17O (8p, 9n) and 18O (8p, 10n), with 16O being the most abundant (99.76%).

The role of isotopes
Every neutron has a weight of around 1.67 * 10-27 kg, which is very little but it matters. 16O is the lightest and 18O the heaviest of the stable isotopes of oxygen. Water – H2O consists of to atoms of hydrogen and one atom of oxygen. Regarding to the abundances of the different isotopes of hydrogen and oxygen most of the water is made of 1H-16O-1H, but there is some water that is consists of 17O or 18O. These water molecules are more difficult evaporate, because they are heavier. But eventually they are evaporated as well. When clouds of water-vapour with the different isotopic compositions start to form raindrops the heavy water molecules are the first ones that precipitate. Scientists compare the amount of 18O and 16O in the water molecules of a sample with a standard.