11 Mar 2022
11 Mar 2022
Status: this preprint is currently under review for the journal CP.

Multimillennial synchronization of low and polar latitude ice cores by matching a time constrained Alpine record with an accurate Arctic chronology

Paolo Gabrielli1,2, Theo Manuel Jenk3,4, Michele Bertó5, Giuliano Dreossi6, Daniela Festi7, Werner Kofler7, Mai Winstrup8, Klaus Oeggl7, Margit Schwikowski3,4,9, Barbara Stenni5, and Carlo Barbante5,6 Paolo Gabrielli et al.
  • 1Byrd Polar and Climate Research Center, The Ohio State University, Columbus, 43210, USA
  • 2School of Earth Sciences, The Ohio State University, 275 Mendenhall Laboratory, Columbus, 43210, USA
  • 3Laboratory of Environmental Chemistry, Paul Scherrer Institut, 5232, Villigen PSI, Switzerland
  • 4Oeschger Centre for Climate Change Research, University of Bern, CH-3012 Bern, Switzerland
  • 5Department of Environmental Sciences, Informatics and Statistics, Ca’ Foscari University of Venice, Venice-Mestre, 30170, Italy
  • 6Institute of Polar Sciences-CNR, Venice-Mestre, 30170, Italy
  • 7Institute for Botany, University of Innsbruck, Innsbruck, 6020, Austria
  • 8DTU Space, Technical University of Denmark, Kongens Lyngby, Denmark
  • 9Department of Chemistry and Biochemistry, University of Bern, CH-3012 Bern, Switzerland

Abstract. We present a novel application of empirical methodologies that significantly reduce the chronological uncertainty of a low latitude-high altitude Alpine ice core record obtained in 2011 from the glacier Alto dell’Ortles (3859 m, Eastern Alps, Italy). A preliminary absolute timescale based on a peak in 3H activity, and 210Pb and 14C analyses on carbonaceous particles and organic remains provided evidence of one of the oldest Alpine ice core records spanning the last ~7000 years, back to the last Northern Hemisphere Climatic Optimum. Here we combine three empirical methods that provide an additional number of time markers that corroborate the multimillennial nature of the Alto dell’Ortles ice cores while significantly decreasing the uncertainty of the chronology. First, 14C analysis of an additional organic fragment (a charred spruce needle) discovered next to the basal ice provides an age (232 ± 126 BCE) which agrees with previous 14C dates in the oldest part of the record. Second, a new millennial-scale high resolution atmospheric Pb depositional record was used to synchronize the Alto dell’Ortles cores with an accurately-dated (±5 years) Pb record from an array of Arctic ice cores during the ~200 BCE to ~1900 CE time period. This match resulted in a shift of the initial Alto dell’Ortles timescale ~200 years earlier, but still within the initial time uncertainty. Third, novel seasonally resolved pollen records from the upper firn/ice portion of the Alto dell’Ortles cores were combined with δ18O and dust annual variations to refine the dating for the 20th century by means of an automatic algorithm (Straticounter; between 2011 and 1927 CE) and visual counting (1926–1900 CE). The time markers obtained by these three methods were combined in a continuous timescale by running a Montecarlo based fit (COPRA model). This Alto dell’Ortles revised chronology shows a significantly reduced uncertainty, between ±1 and ±4 years after 1927 CE, and between a maximum of ±100 years to a minimum of ±5 years between 1927 CE and 200 BCE by conservative estimates. An investigation of the revised chronology by means of a simple 1-D flow model suggests that non-steady-state conditions (e.g., changes in past snow accumulation rate) need to be considered to provide a full physical explanation of the age-depth relationship obtained. The new revised chronology will allow the constraint of the Holocene climatic and environmental histories emerging from this high-altitude glacial archive of Central Europe. The novel methodologies may also be adopted to build or improve the chronologies of other ice cores extracted from-low latitude/high-altitude glaciers that typically suffer from larger dating uncertainties compared with well dated polar records.

Paolo Gabrielli et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-20', Joseph R. McConnell, 04 Apr 2022
  • RC2: 'Comment on cp-2022-20', Anonymous Referee #2, 16 Apr 2022

Paolo Gabrielli et al.

Paolo Gabrielli et al.


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Short summary
We present a methodology that reduces the chronological uncertainty of an Alpine ice core record from the glacier Alto dell’Ortles, Italy. This chronology will allow the constraint of the Holocene climatic and environmental histories emerging from this archive of Central Europe. This method will allow to obtain accurate chronologies also from other ice cores from-low latitude/high-altitude glaciers that typically suffer from larger dating uncertainties compared with well dated polar records.