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Torneträsk tree-ring width and density AD 500 – 2004: A test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
2008 (English)In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 31, 843-857 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents updated tree-ring width(TRW) and maximum density (MXD) from Tornetra¨sk innorthern Sweden, now covering the period AD 500–2004. Byincluding data from relatively young trees for the most recentperiod, a previously noted decline in recent MXD is eliminated.Non-climatological growth trends in the data areremoved using Regional Curve Standardization (RCS), thusproducingTRWandMXDchronologies with preserved lowfrequencyvariability. The chronologies are calibrated usinglocal and regional instrumental climate records. A bootstrappedresponse function analysis using regional climatedata shows that tree growth is forced by April–August temperaturesand that the regression weights for MXD are muchstronger than for TRW. The robustness of the reconstructionequation is verified by independent temperature data andshows that 63–64% of the instrumental inter-annual variationis captured by the tree-ring data. This is a significantimprovement compared to previously published reconstructionsbased on tree-ring data from Tornetra¨sk. Adivergence phenomenon around AD 1800, expressed as anincrease in TRW that is not paralleled by temperature andMXD, is most likely an effect of major changes in the densityof the pine population at this northern tree-line site. The biasintroduced by this TRW phenomenon is assessed by producinga summer temperature reconstruction based onMXDexclusively. The new data show generally higher temperatureestimates than previous reconstructions based onTornetra¨sk tree-ring data. The late-twentieth century, however,is not exceptionally warm in the new record: Ondecadal-to-centennial timescales, periods around AD 750,1000, 1400, and 1750 were equally warm, or warmer. The200-year long warm period centered on AD 1000 was significantlywarmer than the late-twentieth century (p\0.05)and is supported by other local and regional paleoclimatedata. The new tree-ring evidence from Tornetra¨sk suggeststhat this ‘‘Medieval WarmPeriod’’ in northern Fennoscandiawas much warmer than previously recognized.

Place, publisher, year, edition, pages
2008. Vol. 31, 843-857 p.
National Category
Climate Research
Research subject
Physical Geography
URN: urn:nbn:se:su:diva-22690DOI: 10.1007/s00382-007-0358-2ISI: 000260370300007OAI: diva2:189270
Part of urn:nbn:se:su:diva-1034Available from: 2011-02-03 Created: 2006-05-08 Last updated: 2011-02-03Bibliographically approved
In thesis
1. Tree Rings as Sensitive Proxies of Past Climate Change
Open this publication in new window or tab >>Tree Rings as Sensitive Proxies of Past Climate Change
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the boreal forests of the Northern Hemisphere, time series of tree-ring width (TRW) and maximum density in the latewood (MXD) are highly correlated to local instrumental summer-temperature data and are thus widely used as proxies in high-resolution climate reconstructions. Hence, much of our present knowledge about climatic variability in the last millennium is based on tree-rings. However, many tree-ring records have a lack of data in the most recent decades, which severely hampers our ability to place the recent temperature increase in a longer-timescale perspective of natural variability.

The main objective of this thesis is to update and extend the Torneträsk TRW and MXD records in northern Sweden. Local instrumental climate-data is used to calibrate the new tree-ring records. The results show that TRW is mainly forced by temperature in the early growing season (June/July) while MXD has a wider response window (June – August) and has a higher correlation to temperature. Two reconstructions of summer temperature are made for (i) the last 7,400 years based on TRW, and (ii) the last 1,500 years based on a combination of TRW and MXD. The reconstructions show natural variability on timescales from years to several centuries. The 20th century does not stand out as a notably warm period in the long timescale perspective. A medieval period from AD 900 – 1100 is markedly warmer than the 20th century.

The environmental impact from a large explosive volcanic eruption in 1628/1627 BC is analysed in the tree rings of 14C-dated bog pines in south-central Sweden and in absolutely-dated subfossil pines from Torneträsk. The results show evidence of an impact in the southern site at approximately this time but no detectable impact in the North.

Subfossil trees of Fitzroya cupressoides in southern Chile were 14C-dated to approx. 50,000 years BP and amalgamated into a 1,229-year TRW chronology. This tree-ring record is the oldest in the world. The variability in this Last-glacial chronology is similar to the variability in present-day living trees of the same species. These results suggest that the growth–forcing mechanisms 50,000 years ago were similar to those at present.

Place, publisher, year, edition, pages
Stockholm: Institutionen för naturgeografi och kvartärgeologi, 2006. 75 p.
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 1
Tree ring, width, density, climate, temperature, change, variability, sensitivity, Torneträsk, Tornetrask, Sweden, Fennoscandia, explosive, volcanic, eruption, Santorini, Thera, subfossil, Fitzroya, Chile
National Category
Physical Geography
urn:nbn:se:su:diva-1034 (URN)91-7155-251-0 (ISBN)
Public defence
2006-06-02, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00
Available from: 2006-05-08 Created: 2006-05-08Bibliographically approved

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