30 Aug 2022
30 Aug 2022
Status: this preprint is currently under review for the journal GChron.

Bayesian age-depth modelling applied to varve and radiometric dating to optimize the transfer of an existing high-resolution chronology to a new composite sediment profile from Holzmaar (West-Eifel Volcanic Field, Germany)

Stella Birlo1, Wojciech Tylmann2, and Bernd Zolitschka1 Stella Birlo et al.
  • 1University of Bremen, Institute of Geography, GEOPOLAR, Bremen, Germany
  • 2University of Gdańsk, Faculty of Oceanography and Geography, Gdańsk, Poland

Abstract. This study gives an overview of different varve integration methods with Bacon. These techniques will become important for the future as technologies evolve with more sites being revisited for the application of new and high-resolution scanning methods. Thus, the transfer of existing chronologies will become necessary, because the recounting of varves will be too time consuming and expensive to be funded.

We introduce new sediment cores from Holzmaar (West-Eifel Volcanic Field, Germany), a volcanic maar lake with a well-studied varved record. Four different age-depth models (A-D) have been calculated for the new composite sediment profile (HZM19) using Bayesian statistics with Bacon. All models incorporate new Pb-210 and Cs-137 dates for the top of the record, the latest calibration curve (IntCal20) for radiocarbon ages as well as the new age estimation for the Laacher See Tephra. Model A is based on previously published radiocarbon measurements only, while Models B-D integrate the previously published varve chronology (VT-99) with different approaches. Model B rests upon radiocarbon data, while parameter settings are obtained from sedimentation rates derived from VT-99. Model C is based on radiocarbon dates and on VT-99 as several normal-distributed tie-points, while Model D is segmented into four sections: Sections 1 and 3 are based on VT-99 only, whereas Sections 2 and 4 rely on Bacon age-depth models including additional information from VT-99. In terms of accuracy, the parameter-based integration Model B shows little improvement over the non-integrated approach, whereas the tie point-based integration Model C reflects the complex accumulation history of Holzmaar much better. Only the segmented and parameter-based age-integration approach of Model D adapts and improves VT-99 by replacing sections of higher counting errors with Bayesian modelling of radiocarbon ages and thus efficiently makes available the best possible and precise age-depth model for HZM19. This approach will value all ongoing and high-resolution investigations for a better understanding of decadal-scale Holocene environmental and climatic variations.

Stella Birlo et al.

Status: open (until 15 Oct 2022)

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Stella Birlo et al.

Stella Birlo et al.


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Short summary
Sediment cores from volcanic lake Holzmaar provide a very precise chronology based on tree ring-like annual laminations or varves. We statistically combine this varve chronology with radiometric dating and tested three different methods to upgrade the age-depth model. However, only one of the three methods tested improved the dating accuracy considerably. With this work, an overview of different age-integration methods is discussed and made available for increased future demands.