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| Titel |
Blue intensity and density from northern Fennoscandian tree rings, exploring the potential to improve summer temperature reconstructions with earlywood information |
| VerfasserIn |
J. A. Björklund, B. E. Gunnarson, K. Seftigen, J. Esper, H. W. Linderholm |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 10, no. 2 ; Nr. 10, no. 2 (2014-04-30), S.877-885 |
| Datensatznummer |
250116959
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| Publikation (Nr.) |
 copernicus.org/cp-10-877-2014.pdf |
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| Zusammenfassung |
| 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 interannual 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 Δblue intensity
(ΔBI) and Δdensity 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 Δdensity 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. However, even though the new parameter ΔBI
experiences an improvement as well, there are still puzzling dissimilarities
between Δdensity and ΔBI on multicentennial timescales. As
a consequence, temperature reconstructions based on ΔBI 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 ΔBI be used as a reliable proxy in multicentennial-scale
climate reconstructions. |
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