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

A novel laser microparticle detector used in conjunctionwith continuous sample melting has provided a more than 1500 mlong record of particle concentration and size distribution of theNGRIP ice core, covering continuously the period approx. from9.5-100kyr before present; measurements were at 1.65 m depthresolution, corresponding to approx. 35-200yr. Particleconcentration increased by a factor of 100 in the Last GlacialMaximum (LGM) compared to the Preboreal, and sharp variations ofconcentration occurred synchronously with rapid changes in thed18O temperature proxy. The lognormal mode μ of thevolume distribution shows clear systematic variations with smallermodes during warmer climates and coarser modes during colderperiods. We find μ ~ 1.7 μm diameter during LGM andμ ~ 1.3 μm during the Preboreal. On timescales belowseveral 100 years μ and the particle concentration exhibit acertain degree of independence present especially during warmperiods, when μ was also more variable. Using highlysimplifying considerations for the atmospheric transport anddeposition of particles we infer that (i) the observed changes ofμ in the ice largely reflect changes in the size of airborneparticles above the ice sheet and (ii) changes of μ areindicative of changes in long range atmospheric transport time.From the observed size changes we estimate shorter transit timesby roughly 25% during LGM compared to the Preboreal. Theassociated particle concentration increase from more efficientlong range transport is estimated to less than one order ofmagnitude.