Chemical destaining and the delta correction for blue intensity measurements of stained lake subfossil trees

Feng Wang,Gwenaëlle Chaillou,Shulong Yu,Dominique Arseneault,Lily Wang,Steeven Ouellet,Ann Delwaide,Étienne Boucher

doi:10.5194/bg-17-4559-2020

Abstract

Abstract. The stain of wood samples from lake subfossil trees (LSTs) is challenging the wide application of the blue intensity (BI) technique for millennial dendroclimatic reconstructions. In this study, we used seven chemical destaining reagents to treat samples of subfossil black spruce (Picea mariana (Mill.) B.S.P.) trees from two lakes in the eastern Canadian boreal forest. We subsequently compared latewood BI (LBI) and delta BI (DBI) time series along with conventional maximum latewood density (MXD) measured from the stained and destained samples. Results showed that the stain of our samples is most likely caused by postsampling oxidation of dissolved ferrous iron in lake sediments that penetrated into wood. Three reagents (ascorbic acid, sodium ascorbate, and sodium dithionite all mixed with ethylenediaminetetraacetic acid) could remove >90 % of Fe. However, even for the best chemical protocol, a discrepancy of about +2 ∘C compared to MXD data remained in the LBI-based temperature reconstruction due to incomplete destaining. On the contrary, the simple mathematical delta correction, DBI, was unaffected by the Fe stain and showed very similar results compared to MXD data (r>0.82) from annual to centennial timescales over the past ∼360 years. This study underlines the difficulty of completely destaining lake subfossil samples while confirming the robustness of the DBI approach. DBI data measured from stained LSTs can be used to perform robust millennial temperature reconstructions.

Highlights

The blue intensity (BI) technique is an alternative to the more expensive X-ray densitometric methodology in producing proxy parameters such as maximum latewood density (MXD) for dendroclimatology (Björklund et al, 2019; McCarroll et al, 2002)
Excellent coherence was reported between the latewood BI (LBI) and MXD data measured from living-tree materials of a number of coniferous tree species across the Northern Hemisphere (Campbell et al, 2007; Kaczka et al, 2018; Österreicher et al, 2015; Rydval et al, 2014; Wilson et al, 2014), suggesting the potential to use BI method in dendroclimatic reconstructions (McCarroll et al, 2013; Rydval et al, 2017; Wilson et al, 2019)
Our study indicates that the simple delta correction of differentiating latewood and earlywood BI values is more effective to resolve the staining biases of BI data from lake subfossil trees (LSTs) than the much more complex and time-consuming chemical destaining protocols tested here

Summary

Introduction

The blue intensity (BI) technique is an alternative to the more expensive X-ray densitometric methodology in producing proxy parameters such as maximum latewood density (MXD) for dendroclimatology (Björklund et al, 2019; McCarroll et al, 2002). MXD is the most suitable tree-ring parameter for summer temperature reconstructions in northern and high-altitude regions (Esper et al, 2014; Frank and Esper, 2005). Excellent coherence was reported between the latewood BI (LBI) and MXD data measured from living-tree materials of a number of coniferous tree species across the Northern Hemisphere (Campbell et al, 2007; Kaczka et al, 2018; Österreicher et al, 2015; Rydval et al, 2014; Wilson et al, 2014), suggesting the potential to use BI method in dendroclimatic reconstructions (McCarroll et al, 2013; Rydval et al, 2017; Wilson et al, 2019)

Methods

Results

Discussion

Conclusion