Abstract
The continuous development of new proxies as well as a refinement of existing tools are key to advances in paleoclimate research and improvements in the accuracy of existing climate reconstructions. Herein, we build on recent methodological progress in dendroanatomy – the analyses of wood anatomical parameters in dated tree rings – and introduce the longest (1585–2014 CE) dendroanatomical dataset currently developed for North America. We explore the potential of dendroanatomy of high-elevation Engelmann spruce (Picea engelmannii) as a proxy of past temperatures by measuring anatomical cell dimensions of 15 living trees from the Columbia Icefield area. There, X-ray maximum latewood density (MXD) and its blue intensity counterpart (MXBI) have previously been measured, which allows comparing the different parameters. Our findings highlight anatomical MXD and maximum radial cell wall thickness as the two most promising wood anatomical proxy parameters for past temperatures, each explaining 46 % and 49 %, respectively, of instrumental, high-pass filtered, July–August maximum temperatures over the 1901–1994 period. While both parameters display comparable climatic imprinting at higher frequencies to X-ray derived MXD, the anatomical dataset distinguishes itself from its predecessors by providing the most temporally stable warm-season temperature signal. For the long-term secular trends, discrepancies between anatomical MXD and maximum radial cell wall thickness chronologies were observed, where the former more closely follow the long-term variations of the X-ray based MXD. Further studies, including samples from more diverse age cohorts and the adaptation of RCS-based standardizations, are needed to disentangle the ontogenetic and climatic components of long-term signals stored in the wood anatomical traits and to more comprehensively evaluate the potential contribution of this new dataset to paleoclimate research.
Highlights
Tree rings form the backbone of high-resolution palaeoclimatology of the Common Era by providing precisely dated, annually resolved, spatially widespread and accessible archives of climate proxy data
Standardized tree-ring parameter chronologies were assessed for their relationship to regional monthly mean (Tmean) and maximum (Tmax) temperatures, by correlation against the monthly 0.5° x 0.5° gridded CRU TS v4.03 dataset (Harris et al 2020) for the grid point average bounded by the latitude/longitude coordinates 48.25-55.75° N/113.75-123.25° W
The RBAR and Expressed Population Signal (EPS) values for MXBI slightly decrease if computed only on the 15 trees that have been pre-selected for the dendroanatomical analysis
Summary
Tree rings form the backbone of high-resolution palaeoclimatology of the Common Era by providing precisely dated, annually resolved, spatially widespread and accessible archives of climate proxy data. Tree-ring archives make up more than half of all publicly available temperature proxy records and are greatly influential in multi-proxy hemisphericscale temperature reconstructions (PAGES 2k Consortium 2017). They are vital for spatially explicit mapping of important climate periods (e.g., PAGES 2k Consortium 2013), and the study of temporally distinct cooling events caused by volcanic eruptions (e.g., Schneider et al.2015; Stoffel et al 2015; Wilson et al 2016). Ring width may exhibit amplified low-frequency signals (von Storch et al 2004) resulting from lagged growth processes in response to climate (Esper et al 2015) or non-climatic processes (Rydval et al 2015). Björklund et al (2019) showed that increasingly lower resolution of MXD data could result in an increased artificial similarity to the climate response of ring width, and that several of the issues facing ring width as a climate proxy may represent non-negligible constraints on the MXD parameter
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