Geoscience Reference
In-Depth Information
mon tree response to rising
c
a
is an increase in intrinsic water use efficiency (iWUE)
because, with more CO
2
available in the atmosphere, stomata are able to limit water
out of 126 trees sampled for
13
C across Europe showed improvements in iWUE
over the recent past. As iWUE changes, it is possible that the
δ
13
C-climate rela-
tionship in trees will alter, and quite possibly the relationship between tree-ring
width/density and climate. As trees become less sensitive to moistures stress, they
may not respond as strongly to other climatic limiting factors. The rise in
c
a
can be
likened to moving trees from their climatically sensitive ecological limits to more
mesic sites.
δ
The simple answer to this question is probably 'not always.' There are many circum-
stances where stable isotope dendroclimatology will not really produce anything
that could not be produced more cheaply and easily by using ring widths and densi-
ties. However, there are some clear strengths of the isotope approach, which could
be used to good effect.
•
Stable isotopes can display higher signal strengths, in comparison to equivalent
ring width and density series. This does not really matter where material is abun-
dant, but that is rarely the case in the distant past, and the early years of many
reconstructions are not adequately replicated. Where isotope methods could pro-
duce strong climate signals with fewer trees, they could be used to strengthen
existing long chronologies or to produce viable chronologies where material is
sparse.
•
It would seem that, apart from a short juvenile phase in carbon isotope series,
there are no long-term age-related trends in
13
C, and this characteristic probably
δ
18
O and
δ
δ
applies also to
D series. This means that the 'segment length curse'
probably does not apply in extending reconstructions back in time. At present,
there are too few well-replicated, long tree-ring stable isotope chronologies
available to confidently comment on the low-frequency signals that they con-
tain. We can at least say that they have the potential to retain climate information
at the low frequencies that are so difficult to capture by using other approaches.
•
By using more than one isotope series from the same area, and combining them
with other tree-ring proxies, in a multiproxy approach to dendroclimatology, it
may be possible to reconstruct a wider range of climate parameters and also to
detect climatic conditions in the past that do not occur during the relatively short
calibration periods for which meteorological data are available.
•
Stable isotopes may provide access to climate records in tropical trees, though
the very large number of samples required will necessitate a further leap in the
rate at which samples can be analyzed. The most promising approach is likely to
involve linking an ablating laser to an isotope ratio mass spectrometer.
