Measurement of organic carbon in polar snow samples

Glaciers provide a unique medium for the study of palaeoatmos-pheric chemistry1–3, particularly in polar glaciers where chemical records may extend for at least several hundred thousand years. Glaciochemical records from remote, high-latitude areas provide a regional- to global-scale integration of past atmospheric chemistry. These records yield information regarding climate change4–7, volcanic events8,9 and solar activity10, as well as the effect of human activities11,12. Although gaseous forms of organic carbon have been analysed in polar ice13,14, we present here the first measurements, to our knowledge, of organic carbon from polar firn samples. Our measurements are among the lowest reported for organic carbon in precipitation. The data indicate that dissolved organic carbon in Greenland snow has a seasonal deposition pattern, with higher concentrations observed in the winter/spring period. Although we are unable to establish the source of the organic carbon in Greenland snow, three possibilities are discussed