Preprints
https://doi.org/10.5194/bg-2021-119
https://doi.org/10.5194/bg-2021-119

  21 May 2021

21 May 2021

Review status: this preprint is currently under review for the journal BG.

Evaluating the dendroclimatological potential of blue intensity on multiple conifer species from Australasia

Rob Wilson1,5, Kathy Allen2, Patrick Baker2, Sarah Blake3, Gretel Boswijk4, Brendan Buckley5, Edward Cook5, Rosanne D'Arrigo5, Dan Druckenbrod6, Anthony Fowler4, Margaux Grandjean1, Paul Krusic7, and Jonathan Palmer3 Rob Wilson et al.
  • 1School of Earth & Environmental Sciences, University of St. Andrews, UK
  • 2School of Ecosystem and Forest Sciences, University of Melbourne, 500 Yarra Boulevard, Richmond 3121, Australia
  • 3School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia
  • 4Tree-Ring Laboratory, School of Environment, The University of Auckland, Private Bag 92019, Auckland, New Zealand
  • 5Lamont-Doherty Earth Observatory, Palisades, New York 10964, USA
  • 6Department of Geological, Environmental, and Marine Sciences, Rider University, 2083 Lawrenceville Rd, Lawrenceville, NJ, 08648, USA
  • 7Department of Geography, University of Cambridge, Cambridge, UK

Abstract. We evaluate a range of blue intensity (BI) tree-ring parameters in eight conifer species (12 sites) from Tasmania and New Zealand for their dendroclimatic potential, and as surrogate wood anatomical proxies. Using a dataset of ca. 10–15 trees per site, we measured earlywood maximum blue reflectance intensity (EWB), latewood minimum blue reflectance intensity (LWB) and the associated delta blue intensity (DB) parameter for dendrochronological analysis. No resin extraction was performed, impacting low frequency trends. Therefore, we focused only on the high frequency signal by detrending all tree-ring and climate data using a 20-year cubic smoothing spline. All BI parameters express low relative variance and weak signal strength compared to ring-width. Correlation analysis and principal component regression experiments identified a weak and variable climate response for most ring-width chronologies. However, for most sites, the EWB data, despite weak signal strength, expressed strong calibrations with summer temperatures. Significant correlations for LWB were also noted, but the sign of the relationship for most species is opposite to that reported for all conifer species in the Northern Hemisphere. DB performed well for the Tasmanian sites but explained minimal temperature variance in New Zealand. Using the full multi-species/parameter network, excellent summer temperature calibration was identified for both Tasmania and New Zealand ranging from 52 % to 78 % explained variance, with equally robust independent validation (Coefficient of Efficiency = 0.41 to 0.77). Comparison of the Tasmanian BI reconstruction with a wood anatomical reconstruction shows that these parameters record essentially the same strong high frequency summer temperature signal. Despite these excellent results, a substantial challenge exists with the capture of potential secular scale climate trends. Although DB, band-pass and other signal processing methods may help with this issue, substantially more experimentation is needed in conjunction with comparative analysis with ring density and quantitative WA measurements.

Rob Wilson et al.

Status: open (until 04 Jul 2021)

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Rob Wilson et al.

Rob Wilson et al.

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Short summary
We explore Blue Intensity (BI) – a low-cost method for measuring ring density – to enhance palaeoclimatology in Australasia. Calibration experiments, using several conifer species from Tasmania and New Zealand, model 50–80 % of the summer temperature variance. The implications of these results have profound consequences for high-resolution paleoclimatology in Australasia, as the speed and cheapness of BI generation could lead to a step change in our understanding of past climate in the region.
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