30.12.17 Finally some science!
One good thing about working in Antarctica is: you don’t sit in front of the computer all the time. Instead, you start with some REAL tools. Here we are using a heavy wrecking bar and sledge hammer to set up a measuring transect, i.e. a line of bamboo poles, one 500m, one 100 long. I will take snow samples along the transects every day without drifting or blowing snow. In my trench I will do some measurements at the samples and at home they will be analysed in the laboratory.
At the other end of the spectrum, we are running a high-tech measuring device here, called Cavity Ring-Down Spectrometer, or shorter: Picarro (which is just the brand name). The Picarro continuously measures the so-called stable isotope ratio of the water vapor in the air.
What are stable isotopes? Isotopes are simply different types of molecules of the same element, which only have slightly different masses. In case of water vapour or snow (or ice), there are oxygen and hydrogen molecules. They are called stable isotopes in contrast to unstable (=radioactive) isotopes, and here we solely talk about water molecules.
Why do we want to measure them? If you are very interested in the details, you can look it up here:
To learn something about the past climate, one of the most successful methods is the study of ice cores in Greenland or Antarctica. Those cores are about 3000m long and 10cm in diameter and it takes several summer seasons to drill them. Then we can measure different things at the ice cores. For instance, there are air bubbles in the ice that give us information about the former constitution of the atmosphere, particularly about greenhouse gases. The oldest ice that was drilled so far is 800.000 years old! This means it covers 8 ice ages and 8 warm periods! We can also study the chemistry of the ice, e.g. we find volcanic ash from eruptions of volcanoes, which can be used for dating the cores. And then we can look at the ice itself and this gives us information about the air temperature in former climates. And here we need the stable isotopes: We measure the ratio of the different isotopes in the ice core, and this ratio depends in a complex way on the
temperature. The ice in Antarctica, like in any other glacier, is not simply frozen water, like lake ice or sea ice, but it was formed from snow. The snow is compressed under its own weight and gets denser and denser until it becomes ice. This means it is nothing else but former precipitation. Thus, to derive the correct temperature from the stable isotope ratio, we have to understand all atmospheric processes that were involved until the snow fell and also what happened afterwards in the snowpack. More recently, it was found that even in periods without snowfall, the stable isotope ratios of the snow cover changes, following changes in the atmosphere. Here the Picarro comes into the game: we measure the stable isotope ratio of the water vapor in the air above the snow and compare it to that of the snow samples I take. To understand the relationship between the snowpack and the air above it, we use all the meteorological data that are being measured here at Neumayer Station, including upper air data from radiosondes. Thus we have a wealth of data that we can use for process studies and then hopefully apply the results to the interpretation of the deep ice cores in order to get a more exact paleotemperature.