Abstract
Abstract. 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.
Highlights
Ice cores from Greenland contain a record of climate proxies over the last 120 000 years
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
We have found that Greenland ice core dust is dominated by oblate particles of aspect ratio 0.3–0.4, which is significantly different from the aspect ratio of 1 of the polystyrene standard spheres used for calibration
Summary
Ice cores from Greenland contain a record of climate proxies over the last 120 000 years One of those proxies is mineral dust in the size range 0.5–100 μm. The dust has several properties that provide useful information of the past: concentration, size distribution, morphology and chemical and isotopic composition. These measurements have revealed that the dust in ice cores come from central Asia during both the Holocene and the last glacial period (Biscaye et al, 1997). The Coulter counter technique has been used to measure concentration and size distribution It works by measuring the electrical impedance over an orifice through which a sample flows. The Coulter counter has the disadvantage that it applies only to discrete samples and has not been combined with continuous flow analysis (CFA) systems
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