Highly Resolved Paleoclimatic Aerosol Records: Continuous Flow Analysis and the Potential of Flow Cytometry for the Characterisation of Aeolian Dust in Polar Ice Cores

Research output: Book/ReportPh.D. thesisResearch

  • Ernesto Kettner
In ice cores a plethora of proxies for paleoclimatic conditions is archived. Air trapped in the ice during firnification allows for direct measurements of the concentrations and isotope ratios of paleoatmospheric gases while, the isotopic composition of the ice matrix itself is related to paleotemperatures. Impurities in the matrix are comprised of particulate and soluble aerosols, each carrying information on its source’s activitiy and|or proximity. Opposed to gases and water isotopes, the seasonality of many aerosols is not smoothed out in the firn column so that large concentration gradients with frequently changing signs are preserved. Therefore, these aerosol records can be used for dating by annual layer counting. However, with increasing depth the annual layer thicknesses decreases due to pressure and ice flow and accurate dating is possible only as long as the rapid variations can be resolved experimentally.

Over the last decades Continuous Flow Analysis (CFA) has become a well-established technique for aerosol quantification. In CFA, a piece of core is melted continuously and the melt water is analysed for an array of chemical impurities. When designing a CFA system, a trilemma between high sample throughput, high resolution and a large number of detected species is encountered.

In this experimental work, subsequent to contributing to the construction of a CFA system optimised for high resolution, possibilities for the improvement of the insoluble aerosol records’ quality were investigated. Whereas soluble aerosols can be analysed for concentration changes only, insoluble aeolian dust can reveal additional information on its atmospheric residence time via changes in the mean grain sizes.

Volumes of particulate matter in ice cores are most reliably determined with Coulter counters, but since a Coulter counter performs measurements on discrete samples, it cannot be connected to a CFA system. Attenuation sensors, on the other hand, can be integrated into a CFA set-up, but are known to yield poor dust size records.

The dilemma between high quality sizing and high depth resolution was found impossible to circumvent by employing a third detection technique - laser scattering. Reliable information on size changes, even relative ones, cannot be obtained using optical methods. It is therefore proposed to focus further efforts on electrical measurements, making use of the advancements made over the past decade in impedance cytometry.
Original languageEnglish
PublisherThe Niels Bohr Institute, Faculty of Science, University of Copenhagen
Number of pages178
Publication statusPublished - 2013

ID: 98446712