Stable isotope stacks from GRIP and GISP ice cores

Recent efforts to link the isotopic composition of snow in Greenland with meteorological and climatic parameters have indicated that relatively local information such as observed annual temperatures from coastal Greenland sites, as well as more synoptic scale features such as the North Atlantic Oscillation (NAO) and the temperature seesaw between Jakobshaven, Greenland, and Oslo, Norway, are significantly correlated with d18O and dD values from the past few hundred years measured in ice cores. In this study we review those efforts and then use a new record of isotope values from the Greenland Ice Sheet Project 2 and Greenland Ice Core Project sites at Summit, Greenland, to compare with meteorological and climatic parameters. This new record consists of six individual annually resolved isotopic records which have been average to produce a Summit stacked isotope record. The stacked record is significantly correlated with local Greenland temperatures over the past century (r=0.471), as well as a number of other records including temperatures and pressures from specific locations as well as temperature and pressure patterns such as the temperature seesaw and the North Atlantic Oscillation. A multiple linear regression of the stacked isotope record with a number of meteorological and climatic parameters in the North Atlantic region reveals that five variables contribute significantly to the variance in the isotope record: winter NAO, solar irradiance (as recorded by sunspot numbers), average Greenland coastal temperature, sea surface temperature in the moisture source region for Summit (30°-20°N), and the annual temperature seesaw between Jakobshaven and Oslo. Combined, these variables yield a correlation coefficient of r=0.71, explaining half of the variance in the stacked isotope record.

Crystal size variations in Eemian-age ice from the GRIP ice core, Central Greenland

Continuous measurements of ice crystal size have been carried out on an 80 m sequence between 2790 and 2870 m depth in the GRIP ice core from Central Greenland. The ice in this interval is at present considered to orginate 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 ?18O values and crystal size throughout the Eemian, as well as a negative correlation between crystal size and several soluble and insoluble impurities. Although high-resolution impurity records are available from selected parts of the Eemian ice, the study is not conclusive on which impurities are most effective in slowing grain growth. It is shown that the normal grain-growth 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 crystals within the ice sheet and the nucleation and rapid growth of new grains at relatively high temperatures in the lowest part probably play an important role in producing the observed grain-size variations. The relevance of possible flow disturbances of the GRIP Eemian climatic record for the results presented is discussed briefly.