Abstract
The aim of this study is to establish a calibration of the late wood cellulose carbon and oxygen isotopic inter-annual variability measured on four living oaks (1879–1998) in the Atlantic area (Rennes Forest, Brittany, western France) to meteorological (beginning in 1885) and hydrological (beginning in 1951) data. We find a better tree-to-tree consistency of the δ18O ratio, compared with that of the tree-to-tree variability of the ring width and the δ13C possibly affected by individual competition effects.On a century-long time scale, the δ13C ratio in the cellulose reflects the globally decreasing trend of δ13C in atmospheric CO2, which is mainly due to fossil fuel burning. In contrast with the ring width, which here shows a weak and complex dependence on meteorological parameters, the isotopic composition of the cellulose enables a reliable reconstruction (R2 > 0.45), mainly due to the δ18O signal, of selected summer climatic parameters: relative humidity, soil moisture deficit and temperature. The reconstructed parameters capture both low-frequency variations and extreme dry years (summer droughts). While both summer temperature and annual mean precipitation have a long-term increasing trend, the reconstructed water stress indicators do not show a significant trend during the 20th century. On average one summer drought occurs every seven summers, but this frequency varies in parallel to decadal changes in mean summer temperature, with fewer droughts in the 1930s and 1960s–1970s and more droughts in the 1900s, 1940s and 1990s.
Highlights
In order to describe and understand the climate variability during the last few centuries, global-scale temperature reconstructions have been derived
We obtain monthly slopes from June to August of between 0.23 and 0.44‰ ◦C−1, whereas the previous studies obtain values ranging between 0.29 and 0.58‰ ◦C−1. These results show that the summer temperature and relative humidity have a large impact on the cellulose δ18O
We have shown previously that the cellulose isotopes enable a reconstruction of summer temperature, relative humidity or water stress, which is consistent with the available observations in terms of decadal fluctuations and trends
Summary
In order to describe and understand the climate variability during the last few centuries, global-scale temperature reconstructions have been derived. At coastal locations, where the seasonal and interannual temperature and water stress fluctuations are small, these parameters are not clearly influenced by either summer temperature or available soil moisture In such maritime climate areas, other proxies are necessary to obtain quantified climatic reconstructions, such as tree-ring cellulose isotopes. Obtaining reconstructions of the δ18O of the precipitation using a combination of various archives is possible in the North Atlantic regions, and should bring integrated information on the variability of the climate and water cycle In this framework, tree-ring cellulose isotopic measurements offer the possibility to study the δ18O of the precipitation at the inter-annual scale, and to compare the relative performances of cellulose δ13C versus δ18O as climatic tracers (Edwards et al, 2000)
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