Abstract
ABSTRACTHolocene temperature proxy records are commonly used in quantitative synthesis and model‐data comparisons. However, comparing correlations between time series from records collected in proximity to one another with the expected correlations based on climate model simulations indicates either regional or noisy climate signals in Holocene temperature proxy records. In this study, we evaluate the consistency of spatial correlations present in Holocene proxy records with those found in data from the Last Glacial Maximum (LGM). Specifically, we predict correlations expected in LGM proxy records if the only difference to Holocene correlations would be due to more time uncertainty and more climate variability in the LGM. We compare this simple prediction to the actual correlation structure in the LGM proxy records. We found that time series data of ice‐core stable isotope records and planktonic foraminifera Mg/Ca ratios were consistent between the Holocene and LGM periods, while time series of Uk'37 proxy records were not as we found no correlation between nearby LGM records. Our results support the finding of highly regional or noisy marine proxy records in the compilation analysed here and suggest the need for further studies on the role of climate proxies and the processes of climate signal recording and preservation.
Highlights
Palaeoclimate proxy records are invaluable for understanding past climate
As the Holocene is a climate state that is relatively stable, we extend previous investigations of the spatial correlation structure of proxy records (Reschke et al, 2019a), i.e. the similarity of proxy time series depending on the separation distance of sites, to a different climate state with a higher variability in the temperature proxy data: the Last Glacial Maximum (LGM)
To test the current understanding of proxy signals by testing the consistency of the spatial correlation structure of temperature proxy records for different climate states, we predict the spatial correlation expected for LGM proxy records based on the Holocene spatial correlations assuming that the correlation differences are caused only by a different amount of climate variability and time uncertainty between both climate states
Summary
Palaeoclimate proxy records are invaluable for understanding past climate. limited in spatial coverage and affected by uncertainties (e.g. Breitenbach et al, 2012; Lohmann et al, 2013), proxy records are increasingly used in model‐ data comparisons (e.g. Lohmann et al, 2013; Laepple and Huybers, 2014; Marsicek et al, 2018) and quantitative syntheses (e.g. Gajewski, 2015; Harbert and Nixon, 2018; Luoto et al, 2018). Reschke et al (2019a) empirically estimated signal‐to‐noise ratios in compilations of temperature proxy data from the Holocene by comparing the correlations in time series from sites that are in close spatial proximity to one another to those obtained from climate model‐derived time series from the same proxy sites and time period. They found an unexpectedly low correlation among neighbouring proxy sites in contrast to a strong correlation predicted by climate models, indicating either noisy proxy records or climate variations that vary on spatial scales that are too small to be captured by the relatively large‐scale climate models
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