2002 ARCSS All-Hands Workshop

Reconstruction of Summer Temperatures In Interior Alaska From Tree-Ring Proxies: Evidence for changing synoptic climate regimes.

Valerie A. Barber¹, Glenn P. Juday², Bruce P. Finney^3
1Forestry Sciences/Institute of Marine Science, University of Alaska Fairbanks, PO Box 757220, Fairbanks, AK, 99775-7220, USA, Phone (907) 474-7899, barber@ims.uaf.edu
²Department of Forestry Sciences, University of Alaska Fairbanks, PO Box 757200, Fairbanks, AK, 99775, USA, Phone (907) 474-6717, gjuday@lter.uaf.edu
³Institute of Marine Science, University of Alaska Fairbanks, PO Box 757220, Fairbanks, AK, 99775, USA, Phone (907) 474-7724, finney@ims.uaf.edu

Maximum latewood density and d¹³C discrimination of Interior Alaska white spruce were used to reconstruct summer (May through August) temperature at Fairbanks for the period 1800–1996, one of the first high-resolution reconstructions for this region. This combination of latewood density and d¹³C discrimination explains 59.9% of the variance in summer temperature during the period of record 1906–96. The 200 year reconstruction is characterized by 7 decadal-scale regimes. Regime changes are indicated at 1816, 1834, 1879, 1916, 1937, and 1974, are abrupt, and appear to be the result of synoptic scale climate changes. The overall mean summer temperature for the period of reconstruction was 13.49 °C while the recorded was 13.31 °C; the coldest interval was 1916–37 (12.62 °C) and the warmest was 1974–96 (14.23 °C) for the recorded data. The reconstruction is anomalous compared to other Northern Hemisphere records, especially because of interior Alaska warm periods reconstructed from 1834 to 1851 (14.24 °C) and from 1862 to 1879 (14.19 °C). Autogenic effect of tree growth on the site, altered tree sensitivity, or novel combinations of temperature and precipitation cannot be ruled out as contributors to the anomalously warm 19th century reconstruction, but do not appear to be likely. White spruce radial growth is highly correlated with reconstructed summer temperature, and temperature appears to be a reliable index of carbon uptake in this system.

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