Clim. Past Discuss., 9, 6077-6123, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper is under review for the journal Climate of the Past (CP).
A probabilistic model of chronological errors in layer-counted climate proxies: applications to annually-banded coral archives
M. Comboul1, J. Emile-Geay1, M. N. Evans2, N. Mirnateghi1, K. M. Cobb3, and D. M. Thompson4
1Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California, 90089, USA
2Department of Geology, University of Maryland, College Park, Maryland, 20742, USA
3Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive Atlanta, Georgia, 30332, USA
4Department of Geosciences, University of Arizona, 1040 E. 4th Street Tucson, Arizona, 85721, USA

Abstract. The ability to precisely date climate proxies is central to the reconstruction of past climate variations. To a degree, all climate proxies are affected by age uncertainties, which are seldom quantified. This article proposes a probabilistic age model for proxies based on layer-counted chronologies, and explores its use for annually-banded coral archives. The model considers both missing and doubly-counted growth increments (represented as independent processes), accommodates various assumptions about error rates, and allows to quantify the impact of chronological uncertainties on different diagnostics of variability. In one dimension, we find that time uncertainties primarily affect high-frequency signals but also significantly bias the estimate of decadal signals. We further explore tuning to an independent, tree-ring based chronology as a way to identify an optimal age model. In the multivariate case, a synthetic pseudocoral network is used as testing ground to quantify uncertainties in the estimation of spatiotemporal patterns of variability. Even for small error rates, the amplitude of multidecadal variability is systematically overestimated at the expense of interannual variability (ENSO, in this case), artificially flattening its spectrum at periods longer than 10 yr. An approach to correct chronological errors in coherent multivariate records is presented and validated in idealized cases, though it is found difficult to apply in practice due to the large size of the solution space. We end with a discussion of possible extensions of this model and connections to existing strategies for modeling age uncertainties.

Citation: Comboul, M., Emile-Geay, J., Evans, M. N., Mirnateghi, N., Cobb, K. M., and Thompson, D. M.: A probabilistic model of chronological errors in layer-counted climate proxies: applications to annually-banded coral archives, Clim. Past Discuss., 9, 6077-6123, doi:10.5194/cpd-9-6077-2013, 2013.
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