Tree-ring width, and tree-ring stable carbon isotope data from SW Alaska

These data include tree-ring chronologies and stable carbon isotope data
for locations in southwestern Alaska that were used in the study
Decoupling of temperature and growth of white spruce at western treeline,
Alaska is unrelated to intrinsic water stress. The ring-width index (RWI)
chronologies were produced by first removing age-related declines in
growth by fitting a modified negative exponential curve, or a zero-slope
curve if there were no age-related declines, to each ring-width series and
then by averaging the individual indices together using a Tukey bi-weight
robust mean (Cook and Kairiukstis 1990) using the dplR package (Bunn 2008)
in R (R Core Team 2018). RWI is a dimentionless index used for tree ring
chronologies. Carbon stable isotope chronologies were produced for a 30-50
year period from each side. Wood was sub-sampled to alpha cellulose using
the modified Brendel et al. (2005) method (Gaudinski et al. 2011) and
analyzed at the University of Arizona, Environmental Isotope Laboratory.
Uncorrected Carbon isotopes (δ13C) are provided with the units in per mil.
Analytical error is 0.03 per mil. δ13C was converted
to 13C discrimination (Δ13C) to correct for changing atmospheric
δ13CO2 since the Industrial Revolution and is also provided in the data
set.