Articles | Volume 14, issue 5
Clim. Past, 14, 601–608, 2018
Clim. Past, 14, 601–608, 2018

Research article 03 May 2018

Research article | 03 May 2018

Particle shape accounts for instrumental discrepancy in ice core dust size distributions

Marius Folden Simonsen1, Llorenç Cremonesi2, Giovanni Baccolo4, Samuel Bosch1, Barbara Delmonte4, Tobias Erhardt3, Helle Astrid Kjær1, Marco Potenza2, Anders Svensson1, and Paul Vallelonga1 Marius Folden Simonsen et al.
  • 1Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • 2Department of Physics, University of Milan and National Institute for Nuclear Physics (INFN), Via Celoria 16, I20133 Milan, Italy
  • 3Climate and Environmental Physics, Physics Institute & Oeschger Centre for Climate Change Research, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
  • 4Department of Earth and Environmental Sciences, University Milano-Bicocca, Piazza della Scienza 1, I20126 Milan, Italy

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.

Short summary
Ice core dust size distributions are more often measured today by an Abakus laser sensor than by the more technically demanding but also very accurate Coulter counter. However, Abakus measurements consistently give larger particle sizes. We show here that this bias exists because the particles are flat and elongated. Correcting for this gives more accurate Abakus measurements. Furthermore, the shape of the particles can be extracted from a combination of Coulter counter and Abakus measurements.