Abstract

Paleoclimate proxy records have non-negligible uncertainties that arise from both the proxy measurement and the dating processes. Knowledge of the dating uncertainties is important for a rigorous propagation to further analyses; for example for identification and dating of stadial-interstadial transitions in Greenland ice core records during glacial intervals, for comparing the variability in different proxy archives, and for model-data comparisons in general. In this study we develop a statistical framework to quantify and propagate dating uncertainties in layer-counted proxy archives using the example of the Greenland Ice Core Chronology 2005 (GICC05). We express the number of layers per depth interval as the sum of a structured component that represents both underlying physical processes and biases in layer counting, described by a regression model, and a noise component that represents the fluctuations of the underlying physical processes, as well as unbiased counting errors. The age-depth relationship of the joint dating uncertainties can then be described by a multivariate Gaussian process from which realizations of the chronology can be sampled. We show how the effect of an unknown counting bias can be incorporated in our framework and present refined estimates of the occurrence times of Dansgaard-Oeschger events evidenced in Greenland ice cores together with a complete uncertainty quantification of these timings.

Highlights

  • The study of past climates is based on proxy measurements obtained from natural climate archives such as cave speleothems, 15 lake and ocean sediments, and ice cores

  • In this study we develop a 5 statistical framework to quantify and propagate dating uncertainties in layer-counted proxy archives using the example of the Greenland Ice Core Chronology 2005 (GICC05)

  • Using the example of the NGRIP ice core 25 (Andersen et al, 2004) and its associated chronology – the GICC05 (Vinther et al, 2006; Rasmussen et al, 2006; Andersen et al, 2006; Svensson et al, 2008), we present here a statistical approach to generate ensembles of age models that may in turn be used to propagate the age uncertainties to any subsequent analysis of the time series derived from the NGRIP record

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Summary

Introduction

The study of past climates is based on proxy measurements obtained from natural climate archives such as cave speleothems, 15 lake and ocean sediments, and ice cores. Using the example of the NGRIP ice core 25 (Andersen et al, 2004) and its associated chronology – the GICC05 (Vinther et al, 2006; Rasmussen et al, 2006; Andersen et al, 2006; Svensson et al, 2008) – , we present here a statistical approach to generate ensembles of age models that may in turn be used to propagate the age uncertainties to any subsequent analysis of the time series derived from the NGRIP record. An alternative Bayesian approach for quantifying the dating uncertainty of layer counted archives is presented in (Boers 50 et al, 2017), where the uncertainty is shifted from the time axis to the proxy value. This approach does not allow for generation of ensembles of chronologies as required for uncertainty propagation.

NGRIP ice core data
Age-depth model
Linear Regression
Noise structure
Simultaneous Bayesian modeling
Incorporating an unknown counting bias
Dating uncertainty of DO-events
Conclusions
Findings
420 Acknowledgements
Full Text
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