Scaling Properties of Climate Variability as Reconstructed from Different Paleo-Indicators : an Analysis of Holocene Time Series Based on Haar Fluctuations

Holocene climate changes in Arctic and subarctic areas were investigated usingtime series resulting from the analyses of different biological indicators in marine(dinocysts, foraminifers, alkenones) and lake (pollen, chironomids, diatoms)sediment cores (see compilation by Sundqvist et al. Climate of the Past, 2014).These indicators were used to reconstruct climate-related parameters such astemperatures, precipitation, salinity and/or sea-ice cover. Dinocyst, foraminifer and pollen series were usually calibrated with the Modern Analogue Technique (MAT) whereas those from chironomids and diatoms mainly used the Weighted Average Partial Least Square (WAPLS) calibration approach. Hence, the available times series used to document longterm climate changes are heterogeneous since they are based on different indicatorsand different reconstruction methods.In order to document the climate variability captured by the time series, we haveanalyzed the scaling behavior of Holocene records (last 12,000 years) by the meanof the Haar fluctuations (for a given time interval, these are simply the differencesbetween the means of the first and second halves of the interval). Over variousranges of time scale, they can be characterized by exponents H (e.g. [Lovejoy andSchertzer, 2012]). When H<0, fluctuations tend to cancel, the series appears"stable", averaging fluctuations over longer and longer intervals typically yieldssmaller values. When H>0 on the contrary, fluctuations tend to grow with larger timeintervals as the series "wanders" like a drunkard's walk, i.e. it appears "unstable". Weshow how to perform the analyses in a robust fashion, avoiding biases due toirregular sampling and/or variable temporal resolutions. On this basis, wewere able to evaluate whether the signals of different paleo-indicators for thesame location converge at low frequency, or whether they diverge. Even whenconsidering the same core, different indicators sometimes yield diverging signals. Thissuggests variations which could be due to methods of reconstruction or to theclimatic signal recorded by the indicators. Despite divergences in some of the regionalrecords, results consistently show that signals from marine cores tend to bemore stable than those from continental environments.