Continuous record of microparticle concentration and size distribution in the central Greenland NGRIP ice core during the last glacial period

[1] A novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the NGRIP ice core, covering continuously the period approximately from 9.5-100 kyr before present; measurements were at 1.65 m depth resolution, corresponding to approximately 35-200 yr. Particle concentration increased by a factor of 100 in the Last Glacial Maximum (LGM) compared to the Preboreal, and sharp variations of concentration occurred synchronously with rapid changes in the delta(18)O temperature proxy. The lognormal mode mu of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods. We find mu approximate to 1.7 mum diameter during LGM and mu approximate to1.3 mum during the Preboreal. On timescales below several 100 years mu and the particle concentration exhibit a certain degree of independence present especially during warm periods, when m generally is more variable. Using highly simplifying considerations for atmospheric transport and deposition of particles we infer that (1) the observed changes of m in the ice largely reflect changes in the size of airborne particles above the ice sheet and (2) changes of mu are indicative of changes in long range atmospheric transport time. From the observed size changes we estimate shorter transit times by roughly 25% during LGM compared to the Preboreal. The associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude.