Articles | Volume 11, issue 2
Research article
13 Apr 2017
Research article |  | 13 Apr 2017

Linking pollen deposition and snow accumulation on the Alto dell'Ortles glacier (South Tyrol, Italy) for sub-seasonal dating of a firn temperate core

Daniela Festi, Luca Carturan, Werner Kofler, Giancarlo dalla Fontana, Fabrizio de Blasi, Federico Cazorzi, Edith Bucher, Volkmar Mair, Paolo Gabrielli, and Klaus Oeggl

Abstract. Dating of ice cores from temperate non-polar glaciers is challenging and often problematic. However, a proper timescale is essential for a correct interpretation of the proxies measured in the cores. Here, we introduce a new method developed to obtain a sub-seasonal timescale relying on statistically measured similarities between pollen spectra obtained from core samples and daily airborne pollen monitoring samples collected in the same area. This approach was developed on a 10 m core retrieved from the temperate-firn portion of Alto dell'Ortles glacier (Eastern Italian Alps), for which a 5-year annual/seasonal timescale already exists. The aim was to considerably improve this timescale, reaching the highest possible temporal resolution and testing the efficiency and limits of pollen as a chronological tool. A test of the new timescale was performed by comparing our results to the output (date of layer formation) of the mass balance model EISModel, during the period encompassed by the timescale. The correspondence of the results supports the new sub-seasonal timescale based on pollen analysis. This comparison also allows us to draw important conclusions on the post-depositional effects of meltwater percolation on the pollen content of the firn core as well as on the climatic interpretation of the pollen signal.

Short summary
We propose a sub-seasonal timescale based on pollen analyses for a Mt. Ortles firn core. The method can be applied to all types of glaciers, provided the proximity of the pollen source and a negligible time lag between pollen production and its deposition on the glacier. By combining pollen dating with a mass balance model we found evidence that pollen grains are resilient to downward transport by percolating water and that pollen shows a high potential for inferring past climatic conditions.