Geoscience Reference
In-Depth Information
from 425 samples, while the density data comprised measurements made on a sub-
sample of 65 of these trees. Though both the ring-width and density chronologies
spanned more than 1400 years, the greater replication of the data in the ring-width
curve was considered more likely to have produced an 'unbiased' RCS curve (i.e.,
one that is not influenced by residual climate variance in the mean of the mea-
surement data for any specific tree age). A curvilinear (negative exponential) curve
was fitted to the ring width RCS curve, but a straight line was fitted to the den-
chronologies were found to diverge noticeably from each other after about 1800,
with the density chronology exhibiting progressively lower index values. Briffa et al.
actual minus estimated ring widths, derived from a regression using the density data
over the period 501-1750 as the predictor variable, and then removing the recent
apparent decline in the density chronology by adding the fitted straight line values
the AD portion of the Torneträsk chronology (Grudd et al. 2002) and 65 maximum latewood den-
sity series (MXD) from Torneträsk (Briffa et al.
1992
)
: (
a
) curves of 5-year means of average TRW
by ring age created without using pith-offset estimates (
thin line
) and using pith-offset estimates
(
thick line
); (
b
)as(
a
) but using MXD; (
c
) 5-year means of TRW by ring age created by using
pith-offset estimates (
thin line
), modified negative exponential curve fitted to the ring width means
created without using pith-offset estimates (
dashed line
) and age-related spline (
thick line
), fitted
to the first 500 years of ring width means and then linearly extended, created by using pith-offset
estimates; (
d
)as(
c
) but using MXD.
Gray shading
shows ring counts by age without pith-offset
estimates (
a
and
b
) and with pith-offset estimates (
c
and
d
)
