A quantitative comparison of microfossil extraction methods from ice cores

Sandra O Brugger,W Tinner,O Heiri,E Gobet,M Schwikowski,M Sigl,C Schwörer,F R Schanz

doi:10.1017/jog.2018.31

Abstract

ABSTRACTMicrofossil records from ice archives allow vegetation, fire and land-use activity reconstructions on broad spatial scales. Samples typically contain low microfossil concentrations. Therefore, large ice volumes are often needed for palynology. Hence, it is crucial to extract maximum microfossil numbers through appropriate physical-chemical treatments. We compare six methods covering the main water reduction procedures: evaporation, filtration and centrifugation with snow samples. Adding a known number of Lycopodium marker spores prior to sample treatment and a second marker (Eucalyptus) after laboratory processing allows a quantitative microfossil loss assessment during pollen extraction. We applied the best-performing method (average loss of 22%) to high-alpine firn cores from Colle Gnifetti glacier for validation with a natural archive containing extremely low microfossil concentrations. We conclude that samples processed with different microfossil extraction protocols may give different results for pollen concentrations, percentages and ratios between different pollen types, especially if vesiculate conifer pollen is an important pollen assemblage component. We recommend a new evaporation-based method which delivers the smallest and least variable losses among the tested approaches. Since microfossil losses are inevitable during laboratory procedure, adding markers prior to sample processing is mandatory to achieve reliable microfossil concentration and influx estimates.

Highlights

A handful of microfossil records from ice cores and surface snow samples are available at present, probably because the records are difficult to retrieve and the concentrations of the target material are low
Our results clearly show that microfossil loss during pollen extraction from ice samples is inevitable (i.e. >20% of the Lycopodium marker is lost)
The BRUGGER extraction method is developed from existing evaporation-based water reducing methods (e.g. LIU protocol; Liu and others, 1998) with a newly invented step of freezing the tube bottom after centrifugation during the chemical treatment

Summary

Introduction

A handful of microfossil records from ice cores and surface snow samples are available at present (overview in Table 1), probably because the records are difficult to retrieve and the concentrations of the target material are low. In contrast to the more traditional archives of palynology (e.g. lakes and peat bogs), ice archives have specific advantages. They are well suited to address vegetation dynamics and land-use activities at subcontinental scales (Liu and others, 1998), since drilling sites on high-alpine glaciers are remote from microfossil sources and undesired local biases are absent. They do not suffer from fine-scale disturbances that may affect lakes or peatlands such as soil erosion and related reworking issues. Multiproxy climate and environmental evidence from the same cores (e.g. temperature reconstructions or chemical tracers for environmental variables; Eichler and others, 2011) contribute to assess past ecosystem dynamics

Methods

Results

Discussion

Conclusion