Constraining ocean diffusivity from the 8.2 ka event |
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Authors: | Alexander Lorenz Hermann Held Eva Bauer Thomas Schneider von Deimling |
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Institution: | (1) Potsdam Institute for Climate Impact Research (PIK), P.O. Box 60 12 03, 14412 Potsdam, Germany |
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Abstract: | Greenland ice-core data containing the 8.2 ka event are utilized by a model-data intercomparison within the Earth system model
of intermediate complexity, CLIMBER-2.3 to investigate their potential for constraining the range of uncertain ocean diffusivity
properties. Within a stochastic version of the model (Bauer et al. in Paleoceanography 19:PA3014, 2004) it has been possible to mimic the pronounced cooling of the 8.2 ka event with relatively good accuracy considering the timing
of the event in comparison to other modelling exercises. When statistically inferring from the 8.2 ka event on diffusivity
the technical difficulty arises to establish the related likelihood numerically per realisation of the uncertain model parameters:
while mainstream uncertainty analyses can assume a quasi-Gaussian shape of likelihood, with weather fluctuating around a long
term mean, the 8.2 ka event as a highly nonlinear effect precludes such an a priori assumption. As a result of this study
the Bayesian Analysis leads to a sharp single-mode likelihood for ocean diffusivity parameters within CLIMBER-2.3. Depending
on the prior distribution this likelihood leads to a reduction of uncertainty in ocean diffusivity parameters (e.g. for flat
prior uncertainty in the vertical ocean diffusivity parameter is reduced by factor 2). These results highlight the potential
of paleo data to constrain uncertain system properties and strongly suggest to make further steps with more complex models
and richer data sets to harvest this potential. |
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