C01_06

Ultra-small AMS ¹⁴C sample analysis to reconstruct changes in the water availability of the Atacama Desert

Gwozdz M¹, Heinze S¹, Hackenberg G¹, Herb S¹, Stolz A¹, Dewald A¹, Jaeschke A², Rethemeyer J², Schiffer M¹

¹Institute for Nuclear Physics, University of Cologne, Cologne, Germany, ²Institute for Geology and Mineralog, University of Cologne, Cologne, Germany

Traces of plant and microbial life preserved in the hyper-arid soils of the Atacama Desert show a strong dependency on water availability, which is the main controlling factor determining the presence of life. The ultra-small soil samples with 1-20 µg carbon content will be used to reconstruct changes in the water availability. Ultra-small AMS ¹⁴C sample analysis will be applied for determining ages of organic compounds isolated from the desert soils.

The coupling of an isotope ratio mass spectrometer (irMS) to the AMS system will allow online-analysis of ¹⁴C, δ¹³C, and δ¹⁵N of ultra-small samples. δ¹³C values will be used for correction of fractionation in the AMS system, to increase the measurement accuracy and finally, to solve dating problems in different archives of the desert, e.g. sediments from clay pans, phytoliths and lipid bio markers like plant wax lipids.

For the analysis of ultra-small soil samples from the Atacama desert, gas ion source AMS ¹⁴C analysis is applied, due to the achieved reliable results for samples with 2.5-50 µg carbon content and ages higher than 25,000 yr BP. The CO₂ from the sample combustion in an elemental analyzer (EA), which oxidizes solid samples under a constant Helium flow, is split and a small quota is directed towards the irMS, whereas the rest is directed to the AMS ion source by the gas injection system (GIS). While δ¹³C, and δ¹⁵N can be measured with the irMS, the ¹⁴C content is simultaneously measured with the AMS system.