The size distribution of microparticles from selected segments of the Greenland Ice Core Project ice core representing different climatic periods.

Journal of Geophysical Research, Vol. 102, No. C12, p. 26,755-26,763, 1997

J.P. Steffensen
Departement of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen.

The sice distribution of insoluble microparticles (dust) in the particle size 0.4-6.0 µm radius has been measured in more than 1400 samples from the Greenland Ice Core Project (GRIP) deep ice core from Summit, Greenland. The samples were taken from ice core segments representing 32 climatic periods including ice from the Eem interglacial and ice from below the Eemian ice. The mean dust volume distributions from the climatic periods are compared, and the relationship of total dust mass to the concentration of Ca++ and to the stable icotopic composition (δ18O) is investigated. The dust volume distribution are found to be lognormal in the size interval 0.4-2.0 µm with nearly identical shapes. Changes of the lognormal part of the volume distributions are found to be connected to the total dust mass in a systematic way. The total dust mass is correlated to the Ca++ concentration, and data do not show any enrichment in Ca++ from exposed continental shelved due to lower sea levels during the last glacial maximum. The total dust mass is strongly connecterd to δ18O. The volume distribution of the particles in the size interval 2.0-6.0 µm is found to be almost the same in most periods. The exceptions are the "cold" periods in the last part of the last glacial period, where the volume of these particles is higher than in most periods, and the periods from the Eemian and just above the Eemian where the volume of these particles is lower. The volume distributions of both the Eemian "warm" period and the "cold" Eemian events are different from the distributions in ice from both below and above the Eemian ice. Climate changes appear to have modified the processes of production, transport, modification, and deposition of the dust aerosol in the same way over the last 120,000 years or more.