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Blue intensity and density from northern Fennoscandian tree rings, exploring the potential to improve summer temperature reconstructions with earlywood information
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
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2014 (English)In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 10, no 2, 877-885 p.Article in journal (Refereed) Published
Abstract [en]

Here we explore two new tree-ring parameters, derived from measurements of wood density and blue intensity (BI). The new proxies show an increase in the inter-annual summer temperature signal compared to established proxies, and present the potential to improve long-term performance. At high latitudes, where tree growth is mainly limited by low temperatures, radiodensitometric measurements of wood density, specifically maximum latewood density (MXD), provides a temperature proxy that is superior to that of tree-ring widths. The high cost of developing MXD has led to experimentation with a less expensive method using optical flatbed scanners to produce a new proxy, herein referred to as maximum latewood blue absorption intensity (abbreviated MXBI). MXBI is shown to be very similar to MXD on annual timescales but less accurate on centennial timescales. This is due to the fact that extractives, such as resin, stain the wood differentially from tree to tree and from heartwood to sapwood. To overcome this problem, and to address similar potential problems in radiodensitometric measurements, the new parameters Delta blue intensity (Delta BI) and Delta density are designed by subtracting the ambient BI/ density in the earlywood, as a background value, from the latewood measurements. As a case-study, based on Scots pine trees from Northern Sweden, we show that Delta density can be used as a quality control of MXD values and that the reconstructive performance of warm-season mean temperatures is more focused towards the summer months (JJA - June, July, August), with an increase by roughly 20% when also utilising the interannual information from the earlywood. How-ever, even though the new parameter Delta BI experiences an improvement as well, there are still puzzling dissimilarities between Delta density and Delta BI on multicentennial timescales. As a consequence, temperature reconstructions based on Delta BI will presently only be able to resolve information on decadal-to- centennial timescales. The possibility of trying to calibrate BI into a measure of lignin content or density, similarly to how radiographic measurements are calibrated into density, could be a solution. If this works, only then can Delta BI be used as a reliable proxy in multicentennial-scale climate reconstructions.

Place, publisher, year, edition, pages
2014. Vol. 10, no 2, 877-885 p.
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-104452DOI: 10.5194/cp-10-877-2014ISI: 000335374600031OAI: diva2:723240


Available from: 2014-06-10 Created: 2014-06-10 Last updated: 2014-06-10Bibliographically approved

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Gunnarson, Björn E.
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Department of Physical Geography and Quaternary Geology
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