T. Thorsteinsson et al., CRYSTAL SIZE VARIATIONS IN EEMIAN-AGE ICE FROM THE GRIP ICE CORE, CENTRAL GREENLAND, Earth and planetary science letters, 131(3-4), 1995, pp. 381-394
Continuous measurements of ice crystal size have been carried out on a
n 80 m sequence between 2790 and 2870 m depth in the GRIP ice core fro
m Central Greenland. The ice in this interval is at present considered
to originate from the Eemian interglacial period. The record reveals
that the crystal size in ice older than 100,000 yr is highly dependent
on climatic conditions at the time of snowfall. This dependence shows
up as a strong correlation between delta(18)O values and crystal size
throughout the Eemian, as well as a negative correlation between crys
tal size and several soluble and insoluble impurities. Although high-r
esolution impurity records are available from selected parts of the Ee
mian ice, the study is not conclusive on which impurities are most eff
ective in slowing grain growth. It is shown that the normal grain-grow
th process, commonly observed in the upper few hundred metres of polar
ice sheets, does not yield grain sizes compatible with observed ones
at this depth in the ice sheet, even in those parts of the Eemian ice
where impurity drag effects are not present. Polygonization of crystal
s within the ice sheet and the nucleation and rapid growth of new grai
ns at relatively high temperatures in the lowest part probably play an
important role in producing the observed grain-size variations. The r
elevance of possible flow disturbances of the GRIP Eemian climatic rec
ord for the results presented is discussed briefly.