Anomaly Detection in Paleoclimate Records using Information Theory
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The Shannon entropy rate can be useful in identifying anomalies in high-resolution paleoclimate data records, including noise, outliers, and post-processing issues. We demonstrate this using calculations of weighted permutation entropy (WPE) on water-isotope records in a deep polar ice core. In one region of the isotope records, WPE calculations revealed a significant jump in the amount of new information present in the time series at each point. We conjectured that this effect was due to noise introduced by an older laboratory instrument. In this paper, we validate that conjecture by re-analyzing a section of the ice core using a more-advanced version of the laboratory instrument. The anomalous noise levels are absent from the WPE trace of the new data. In other sections of the core, we show that WPE can be used to identify anomalies in the raw data that are not associated with climatic or glaciological processes, but rather effects occurring during ice sampling, analysis, or data post-processing. These examples make it clear that WPE is a useful forensic tool for identifying sections of data that requires targeted re-analysis, or even a wholly new data set.
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