Constraining the age of Lateglacial and early Holocene pollen zones and tephra horizons in southern Sweden with Bayesian probability methods

• Published in: Journal of Quaternary Science
• Main Authors: Wohlfarth, B., Blaauw, M., Davies, S. M., Andersson, M., Wastegård, S., Hormes, A., Possnert, G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2006
• Subjects: Askja; ice core
• Online Access: http://dx.doi.org/10.1002/jqs.996; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjqs.996; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jqs.996

Abstract The sediment sequence from Hässeldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hässeldalen Tephra and the 10‐ka Askja Tephra. Twenty‐eight high‐resolution 14 C measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono‐ and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hässeldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and ‘realistic’ age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hässeldala port are large and calendar year estimates differ according to the assumptions of the age‐model. Not only do these results provide a cautionary note for over‐dependence on one age‐model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age–depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons. Copyright © 2006 John ...