18.104.22.168. Physical and chemical characteristics of ice cores
The occurrence of melt features in the upper layers of ice cores are of particular palaeoclimatic significance. Such features include horizontal ice lenses and vertical ice glands which have resulted from the refreezing of percolating water (Langway, 1970; Koerner, 1977a). They can be identified by their deficiency in air bubbles. The relative frequency of melt phenomena may be interpreted as an index of maximum summer temperatures or of summer warmth in general (Koerner, 1977b). Other physical features of ices cores which offer information to the palaeoclimatologist include variations in crystal size, air bubble fabric and crystallographic axis orientation (Langway, 1970).
Another important component of ice cores which is of palaeoclimatic significance is the atmospheric gas content, as the air pores are closed off during the densification of firn to ice (Raynaud & Lorius, 1973). Considerable research effort has been devoted to the analysis of carbon dioxide concentrations of air bubbles trapped in ice cores. It will be seen in chapter 5 that variations in atmospheric carbon dioxide may have played an important role in the glacial-interglacial climatic variations during the Quaternary.
Finally, variations of particulate matter, particularly calcium, aluminium, silicon and certain atmospheric aerosols can also be used as proxy palaeoclimatic indicators (Koerner, 1977b; Petit et al., 1981).