Eventually they are isolated from exchange with the atmosphere, thus preserving a sample of air from a time gone past. Ice sheets can be a few kilometers thick and can contain ice that fell as snow over 100,000 years ago. By drilling through the ice and collecting a core, we sample the record of Earth's changing atmosphere. Left to right are Joey Tsai, Dr. Albert, Nancy Cloud and Sandy. The project I worked on examined how various chemical components of the atmosphere become a part of the snow and firn.
Some atmospheric components are more active chemically than others.
This difference in activity causes the various components to be incorporated into and move through the snow at different rates. We also are looking at how energy from sunlight hitting the snow and firn affects the behavior of chemical species. We need to know just how the various chemical species behave so that we can make the best possible interpretation of ice core data. One issue scientists need to deal with is what length of time is represented by an air bubble trapped in the ice. Because it takes a while for these pockets of air to be sealed off from the atmosphere by accumulation of snow above them, data from a chemical species that is known to not move far in snow and firn can be used to create a much more detailed picture of past atmospheres than data from chemical species that commonly migrate long distances.