{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,30]],"date-time":"2026-04-30T03:41:00Z","timestamp":1777520460865,"version":"3.51.4"},"reference-count":41,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2018,12,5]],"date-time":"2018-12-05T00:00:00Z","timestamp":1543968000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100000001","name":"National Science Foundation","doi-asserted-by":"publisher","award":["1807478"],"award-info":[{"award-number":["1807478"]}],"id":[{"id":"10.13039\/100000001","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>Permutation entropy techniques can be useful for identifying anomalies in paleoclimate data records, including noise, outliers, and post-processing issues. We demonstrate this using weighted and unweighted permutation entropy with water-isotope records containing data from a deep polar ice core. In one region of these isotope records, our previous calculations (See Garland et al. 2018) revealed an abrupt change in the complexity of the traces: specifically, in the amount of new information that appeared at every time step. We conjectured that this effect was due to noise introduced by an older laboratory instrument. In this paper, we validate that conjecture by reanalyzing a section of the ice core using a more advanced version of the laboratory instrument. The anomalous noise levels are absent from the permutation entropy traces of the new data. In other sections of the core, we show that permutation entropy techniques can be used to identify anomalies in the data that are not associated with climatic or glaciological processes, but rather effects occurring during field work, laboratory analysis, or data post-processing. These examples make it clear that permutation entropy is a useful forensic tool for identifying sections of data that require targeted reanalysis\u2014and can even be useful for guiding that analysis.<\/jats:p>","DOI":"10.3390\/e20120931","type":"journal-article","created":{"date-parts":[[2018,12,5]],"date-time":"2018-12-05T12:22:00Z","timestamp":1544012520000},"page":"931","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":33,"title":["Anomaly Detection in Paleoclimate Records Using Permutation Entropy"],"prefix":"10.3390","volume":"20","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-6724-2755","authenticated-orcid":false,"given":"Joshua","family":"Garland","sequence":"first","affiliation":[{"name":"Santa Fe Institute, 1399 Hyde Park Rd., Santa Fe, NM 87501, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1871-2105","authenticated-orcid":false,"given":"Tyler R.","family":"Jones","sequence":"additional","affiliation":[{"name":"Institute for Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8813-6524","authenticated-orcid":false,"given":"Michael","family":"Neuder","sequence":"additional","affiliation":[{"name":"Department of Computer Science, University of Colorado Boulder, Boulder, CO 80309, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8105-585X","authenticated-orcid":false,"given":"Valerie","family":"Morris","sequence":"additional","affiliation":[{"name":"Institute for Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6041-4684","authenticated-orcid":false,"given":"James W. C.","family":"White","sequence":"additional","affiliation":[{"name":"Institute for Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO 80309, USA"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4567-2543","authenticated-orcid":false,"given":"Elizabeth","family":"Bradley","sequence":"additional","affiliation":[{"name":"Santa Fe Institute, 1399 Hyde Park Rd., Santa Fe, NM 87501, USA"},{"name":"Department of Computer Science, University of Colorado Boulder, Boulder, CO 80309, USA"}]}],"member":"1968","published-online":{"date-parts":[[2018,12,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"617","DOI":"10.5194\/amt-10-617-2017","article-title":"Improved methodologies for continuous-flow analysis of stable water isotopes in ice cores","volume":"10","author":"Jones","year":"2017","journal-title":"Atmos. Meas. Tech."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"137","DOI":"10.3189\/2014AoG68A016","article-title":"The 1500 m South Pole ice core: Recovering a 40 ka environmental record","volume":"55","author":"Casey","year":"2014","journal-title":"Ann. Glaciol."},{"key":"ref_3","unstructured":"(2018, December 04). East Greenland Ice Core Project. Available online: https:\/\/eastgrip.org\/."},{"key":"ref_4","unstructured":"There are some replicate data available from shallow snow pits [5] or closely drilled shallow ice cores [6]."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1565","DOI":"10.5194\/cp-12-1565-2016","article-title":"Regional climate signal vs. local noise: A two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land","volume":"12","author":"Kipfstuhl","year":"2016","journal-title":"Clim. 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By contrast, solid diffusion is extremely slow, but over very long time periods\u2014tens of thousands of years\u2014can have substantial effects. Mixing and diffusion also occur in the CRDS-CFA system [1], but these effects are small compared to firn and solid-ice diffusion."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"290","DOI":"10.1002\/2016JF003938","article-title":"Water isotope diffusion in the WAIS Divide ice core during the Holocene and last glacial","volume":"122","author":"Jones","year":"2017","journal-title":"J. Geophysci. Res. Earth Surf."},{"key":"ref_23","unstructured":"This spacing is also affected by changes in yearly snow accumulation, obviously. 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Glaciol."},{"key":"ref_41","unstructured":"Indeed, the frequency shift may magnify the impact of noise on that calculation."}],"container-title":["Entropy"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1099-4300\/20\/12\/931\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T15:31:25Z","timestamp":1760196685000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1099-4300\/20\/12\/931"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,12,5]]},"references-count":41,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2018,12]]}},"alternative-id":["e20120931"],"URL":"https:\/\/doi.org\/10.3390\/e20120931","relation":{},"ISSN":["1099-4300"],"issn-type":[{"value":"1099-4300","type":"electronic"}],"subject":[],"published":{"date-parts":[[2018,12,5]]}}}