Samara Willcocks, of Balclutha Primary School, asks :-

What is in the bubbles in iceblocks?

Kate Sinclair, a glaciologist at GNS Science, responded.

The New Zealand Ice Core Program, which is based at GNS Science, obtains and studies ice cores from the Ross Sea Region in Antarctica. The analysis of trapped air bubbles in ice is one of the most interesting aspects of our work. This part of the work is carried out by GNS Science's National Isotope Centre.

The bubbles in ice blocks in your freezer contain a tiny sample of air, which is made up of mostly nitrogen and oxygen, with smaller amounts of argon, and greenhouse gases such as carbon dioxide, methane and nitrous oxide. In a similar way, the bubbles in glacier ice trap small amounts of air that can tell us a lot about how earth’s climate has changed over time.

As snow falls on a glacier or ice sheet it is buried and becomes compressed by the weight of new snowfall above. It then begins a slow transformation to hard glacier ice. About 40 metres below the surface, true glacier ice forms and tiny air bubbles are sealed into the ice. This air gives us a picture of what the earth’s atmosphere was like at the time when the bubbles were trapped within the ice.

Extracting these bubbles and analysing the gases that are trapped in the ice is not easy. Firstly, we need to drill an ice core to recover a climate record. These cores are drilled vertically into the ice and are pulled out metre-by-metre and shipped to New Zealand. We then carefully extract the air that is trapped in each section of ice core and measure the gases in each sample. We are mostly interested in the greenhouse gases because they play an important role in controlling the temperature of the earth. By measuring the concentration of these gases, we can then get a very good idea of how these gases have changed over time, and how these changes have affected the climate of the planet.