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Rights: Thin Ice/University of Waikato
Published 11 April 2017

Dr Nancy Bertler explains how ice cores are sampled for chemical and isotopic analyses for past temperature, wind, sea ice extent, snow source and other variables.


Dr Nancy Bertler

Everything that you see on a periodic table, everything that’s in the atmosphere, everything that’s being breathed or evaporated out of the oceans, dust that comes off the continents, we find literally everything in the ice.

This is our core. I’m working on this one. So I’m loading the next Antarctic core onto the melter now. It’s not the easiest of jobs, it’s a little bit fiddly.

It melts the ice core layer by layer, back through time, and as the water is produced, it is pumped by these pumps into these various tubes, and this allows us to do analysis on all sorts of things that are contained in these ice cores.

Some of the elements that we measure, we measure in parts per quadrillion, and to visualise that or to get a feel for what that actually means is we are looking for a second in 33 million years. We see traces of nuclear bomb testing. So we are looking for dust as an indicator of wind strength. We are looking for properties of the water that tell us about the temperature, where this air mass may have come from that precipitated the snow. You could almost say we are taking the DNA of the atmosphere.

In the ice cores, there are little bubbles, and those bubbles contain a real sample of the atmosphere through time. We can release that air and measure the greenhouse gases, and so by studying how much of these various components are in the ice, we get a feel for what climate was like at the time when the snow fell.

If you take all these records together from across the continent, there are some very strong messages that stand out, and these are really that the last 50–150 years were vastly different from the last 1,000 or 10,000 years. For example, we look at the hydrogen, oxygen, the stable isotopes of water, which gives us a very good indication of temperature at the continent, and it has increased over the last 50 years or 150 years.

So if we view something like CO2, it has remained at pretty much 280 ppm over the last 1,000 or 10,000 years. Right now, we are already 386 I think.

We look at things like methyl sulfonate. This is produced by bacteria that lives in the sea ice, and therefore we measure their productivity in the ice cores, and it tells us sea ice has changed.

If we look, for example, at certain chemistry in the ice core, for example, the marine elements from the ocean, we can see that these westerly winds that circumnavigate the Antarctic have intensified and came closer to Antarctica.

If Antarctica is changing, it will have very fundamental consequences for the rest of the planet – like sea level, productivity of the oceans, the heat budget of the globe, zone tracks, wave patterns, things that we don’t even know yet how they will be impacted by these changes.


This video is an extract from Thin Ice – The Inside Story of Climate Science, a David Sington/Simon Lamb film.

The full documentary film is available by emailing The link for streaming is available free of charge. The DVD is also available to New Zealand schools for $20 to cover costs.

© Thin Ice/University of Waikato