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The Klotz Abakus laser sensor and the Coulter counter are both used for measuring the size distribution of insoluble mineral dust particles in ice cores. While the Coulter counter measures particle volume accurately, the equivalent Abakus instrument measurement deviates substantially from the Coulter counter. We show that the difference between the Abakus and the Coulter counter measurements is mainly caused by the irregular shape of dust particles in ice core samples. The irregular shape means that a new calibration routine based on standard spheres is necessary for obtaining fully comparable data. This new calibration routine gives an increased accuracy to Abakus measurements, which may improve future ice core record intercomparisons. We derived an analytical model for extracting the aspect ratio of dust particles from the difference between Abakus and Coulter counter data. For verification, we measured the aspect ratio of the same samples directly using a single-particle extinction and scattering instrument. The results demonstrate that the model is accurate enough to discern between samples of aspect ratio 0.3 and 0.4 using only the comparison of Abakus and Coulter counter data.

Atmospheric dust is an active component of the climate system. Paleo dust records fromthe early Holocene and Eemian, which were both a few degrees warmer than today, are usedto constrain models of a future warmer climate. Ice core records provide a strong tie pointfor paleo dust models, as they have a high temporal resolution and are representative of alarge geographical area. However no insoluble dust record from Greenland of the Holoceneand Eemian has so far been published. This is partly due to the low dust concentrationin the ice, which demands high accuracy from the instruments.Long ice core dust concentration and size distribution records are often measuredby Abakus laser sensor. Abakus measurements deviate from measurements by the moreaccurate Coulter Counter, and the discrepancy can not be solved by a simple calibration.In this thesis it is shown that the discrepancy between the Coulter Counter and the Abakusis due to the non-spherical shape of the particles. The Abakus is strongly inuenced by Miescattering when measuring standard polystyrene spheres, while the Mie scattering eectscancel out for real dust particles due to their variable shape, as shown by AmsterdamDiscrete Dipole Approximation simulations. Furthermore, the Abakus assigns a largersize to the particles than the Coulter Counter, since the particles are elongated. A SingleParticle Extinction and Scattering Instrument (SPES) was used to measure an aspect ratioof 0:390:03 for local east Greenlandic dust and 0:330:03 for remote Asian dust in theeast Greenlandic RECAP ice core. The aspect ratio derived from the discrepancy betweenthe Coulter Counter and Abakus agrees with the SPES results, and local and remote dustcan be easily discerned. If the aspect ratio is known, the Abakus can be calibrated to theCoulter Counter, so it gives accurate concentrations and size distributions.The RECAP ice core was drilled in 2015 on the Renland ice cap by the East Greenlandcoast. Its dust record has been measured