Discussion article about a new vegetation proxy in speleothems and cave drip water published

Quest members from Mainz have published an article about the analysis of lignin oxidation products as vegetation proxies in speleothem and cave drip water samples in the discussion part of Biogeosciences. They developed a sensitive method to analyse the lignin composition of organic traces contained in speleothems. Lignin is a main constituent of woody plants and its composition contains information about the type of vegetation. This method offers new possibilities to reconstruct the vegetation of past millenia since it combines the advantages of lignin analysis as a highly specific vegetation biomarker with the benefits of speleothems as unique terrestrial climate archives.

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Novel numerical method to analyse multivariate proxy records

Members of the QUEST team have published a new approach for analysing multivariate proxy records with recurrence networks. The idea is to first consider each proxy separately as a recurrence network, then combine them as layers of a multiplex network, and derive a similarity measure from this resulting multiplex recurrence network. This approach can be used to reveal periods of converging dynamics or very disperse variability, as demonstrated on an example of palaeo vegetation development during the last 16 ka in East Asia.

Multiplex recurrence network

Multiplex recurrence network

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New study on short time series published

The “inner composition alignment approach” (IOTA) has been suggested in the past for detecting interdependencies between short time series. QUEST members have now published a new study with a modification of this approach (called mIOTA). The new extension overcomes the drawbacks that IOTA is unable to distinguish between positive and negative correlations, and that the null distribution for IOTA is biased towards higher values. Although the new method cannot detect the direction of the interdependencies (unlike IOTA), it outperforms standard tools for detecting interdependencies (Pearson correlation, Spearman correlation, Kendall’s τ). The method is used to derive econo-climatic networks of interdependencies between economic indicators and climatic variability for Sub-Saharan Africa and South Asia including India.

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Important step forward to recurrence analysis of data with uncertainties

In a new publication we propose a novel approach for analysing data with uncertainties, which is typical, e.g., in palaeoclimate observations. A time series of single values is replaced by a time series of probabilities; the binary matrix representation of recurrences is then replaced by  a matrix of probability values, which represent that a recurrence at a certain time appears. This approach is the base for a novel transition test, applying concepts from recurrence and complex network analysis. We demonstrate the potentials on examples from present-day climate (ENSO), palaeoclimate (Indian summer monsoon), and stock markets.

probability series

Time series of probability distributions of proxy values, allowing for uncertainty analysis.

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