17 May 2022
17 May 2022
Status: this preprint is currently under review for the journal CP.

Non-spherical microparticle shape in Antarctica during the last glacial period affects dust volume-related metrics

Aaron Chesler1,2,a, Dominic Winski1,2, Karl Kreutz1,2, Bess Koffman3, Erich Osterberg4, David Ferris4, Zayta Thundercloud4, Joseph Mohan1,5, Jihong Cole-Dai6, Mark Wells7, Michael Handley1, Aaron Putnam2, Katherine Anderson4, and Natalie Harmon2 Aaron Chesler et al.
  • 1Climate Change Institute, University of Maine, Orono, Maine, 04469, USA
  • 2School of Earth and Climate Sciences, University of Maine, Orono, Maine, 04469, USA
  • 3Department of Geology, Colby College, Waterville, Maine, 04903, USA
  • 4Department of Earth Science, Dartmouth College, Hanover, New Hampshire, 03755, USA
  • 5Ecology and Environmental Sciences, University of Maine, Orono, Maine, 04469, USA
  • 6Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota, 57007
  • 7School of Marine Sciences, University of Maine, Orono, Maine, 04469, USA
  • anow at: Environmental Studies Program, Goucher College, Towson, Maryland, 21204, USA

Abstract. Knowledge of microparticle geometry is essential for accurate calculation of ice core volume-related dust metrics (mass, flux, and particle size distributions) and subsequent paleoclimate interpretations, yet particle shape data remain sparse in Antarctica. Here we present 41 discrete particle shape measurements, volume calculations, and calibrated continuous particle timeseries spanning 50 – 10 ka from the South Pole Ice Core (SPC14) to assess particle shape characteristics and variability. We used FlowCAM, a dynamic particle imaging instrument, to measure aspect ratios (width divided by length) of microparticles. We then compared those results to Coulter Counter measurements on the same set of samples as well as high-resolution laser-based (Abakus) data collected from the SPC14 core during continuous flow analysis. The 41 discrete samples (~490 years per sample in the Last Glacial Maximum; LGM) were collected during three periods of rapid global climate reorganization: Heinrich Stadial 1 (18 – 16 ka, n = 6), the LGM (27 – 18 ka, n = 19), and during Heinrich Stadial 4 (42 - 36 ka) and Heinrich Stadial 5 (50 – 46 ka, n = 16). Using FlowCAM measurements, we calculated different particle size distributions (PSDs) for spherical and ellipsoidal volume estimates. Our calculated volumes were then compared to published Abakus calibration techniques. We found that Abakus-derived PSDs calculated assuming ellipsoidal, rather than spherical, particle shapes provide a more accurate representation of PSDs measured by Coulter Counter, reducing Abakus-to-Coulter Counter flux and mass ratios from 1.82 (spherical assumption) to 0.79 and 1.20 (ellipsoidal assumptions; 1 being a perfect match). Coarser particles (>5.0 µm diameter) show greater variation in measured aspect ratios than finer particles (<5.0 µm). While fine particle volumes can be accurately estimated using the spherical assumption, applying the same assumption to coarse particles has a large effect on inferred particle volumes. Temporally, coarse and fine particle aspect ratios do not significantly change within or among the three time periods (p-value > 0.05), suggesting that long range transport of dust is likely dominated by clay minerals and other elongated minerals.

Aaron Chesler et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-36', Anonymous Referee #1, 19 Jun 2022
    • AC1: 'Reply on RC1', Aaron Chesler, 19 Aug 2022
  • RC2: 'Comment on cp-2022-36', Anonymous Referee #2, 08 Jul 2022
    • AC2: 'Reply on RC2', Aaron Chesler, 19 Aug 2022

Aaron Chesler et al.

Data sets

South Pole (SPC14) microparticle concentration, mass concentration, flux, particle-size-distribution mode, and aspect ratio measurements Karl Kreutz

Aaron Chesler et al.


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Short summary
Ice core microparticle data typically use geometry assumptions to calculate particle mass and flux. We use dynamic particle imaging, a novel technique for ice core dust analyses, combined with traditional laser particle counting and coulter counter techniques to assess particle shape in the South Pole Ice Core (SPC14) spanning 50 – 10 ka. Our results suggest that particles are dominantly ellipsoidal in shape and that spherical assumptions overestimate particle mass and flux.