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OC3 - High resolution dust measurements in ice cores
Hubertus Fischer, Anna Wegner, Katrin Wolff
Mineral dust in Greenland ice cores exhibits systematic variations of size distribution and particle concentration changes. The concentration of dust is low during warm periods while cold phases correspond to high particle concentration. The lowest dust concentration (insoluble particle mass concentration C_M = 70 µg/kg) has been found for the Preboreal (~11 500 - 10 000 years before present, BP) and the highest (C_M = 8000 µg/kg) for the Last Glacial Maximum as determined in an earlier study by Ruth et al. (2003). Variations by a factor of 8 of C_M were encountered across the rapid Dansgaard/Oeschger transitions. Regarding the size distribution, larger particles were found during colder climates and vice versa. Values for the modal value of the size distribution µ are around 1.3 µm in the Preboreal and around 1.7 µm during the Last Glacial Maximum. The variability of dust concentrations in Greenlandic ice cores is due to changes both during transport and in the dust sources which have been identified as the East Asian deserts.
Further investigations regarding a higher resolution of dust deposition are in progress. The aim of the project is to study the dust deposition at seasonal-to-interannual resolution using dust concentration and size measurements on selected time slices in the North-GRIP ice core covering the period approximately from 50 000 yr BP until 2000 yr BP. The goal is to reconstruct seasonal transport trajectories of mineral dust from the source region to Greenland and to analyse seasonal changes in the transport strength.
A method to achieve very high resolution data was already developed by Wegner (2008) for measurements in an Antarctic ice core, which show seasonal variability in dust concentration and size (see Fig. 1 for an example). For the measurements in the Greenland ice cores, the method will be further developed during this project.
References:
Ruth et al. (2003): Continuous record of microparticle concentration and size distribution in the central Greenland NGRIP ice core during the last glacial period, J. Geophys. Res., 108.
Wegner, A. (2008): Sources and Transport Characteristics of Mineral Dust in Dronning Maud Land, Antarctica, Ph. D. Thesis, University of Bremen.
Figure 1: Dust in the EDML1083 ice core section. Dust mass concentration measured by Coulter Counter (red line) and modal values of the log-normal distribution fitted to the mass distribution (blue line). The profile taken from the last Glacial (~26 000 yr BP) shows a clear seasonality with dust mass and size in phase.