A bi-proxy reconstruction of Fontainebleau (France) growing season temperature from A.D. 1596 to 2000

摘要

In this paper, we develop a new methodology to estimate past changes ofgrowing season temperature at Fontainebleau (northern France). NorthernFrance temperature fluctuations have been documented by homogenisedinstrumental temperature records (at most 140 year long) and by grapeharvest dates (GHD) series, incorporated in some of the European-scaletemperature reconstructions. We have produced here three new proxy records:δ18O and δ13C of latewood cellulose of livingtrees and timbers from Fontainebleau Forest and Castle, together with ringwidths of the same samples. δ13C data appear to be influencedby tree and age effects; ring widths are not controlled by a single climateparameter. By contrast, δ18O and Burgundy GHD series exhibitstrong links with Fontainebleau growing season maximum temperature. Each ofthese records can also be influenced by other factors such as vine growingpractices, local insolation, or moisture availability. In order to reducethe influence of these potential biases, we have used a linear combinationof the two records to reconstruct inter-annual fluctuations of Fontainebleaugrowing season temperature from 1596 to 2000. Over the instrumental period,the reconstruction is well correlated with the temperature data(R2=0.60).This reconstruction is associated with an uncertainty of ~1.1°C(1.5 standard deviation), and is expected to provide a reference series forthe variability of growing season maximum temperature in Western Europe.Spectral analyses conducted on the reconstruction clearly evidence (i) theinterest of combining the two proxy records in order to improve the powerspectrum of the reconstructed versus observed temperature, (ii) changes inthe spectral properties over the time, with varying weights of periodicitiesranging between ~6 and ~25 years. Available reconstructions ofregional growing season temperature fluctuations get increasingly divergentat the interannual or decadal scale prior to 1800. Our reconstructionsuggests a warm interval in the late 17th century, with the 1680s aswarm as the 1940s, followed by a prolonged cool period from the 1690s to the1850s culminating in the 1770s. The persistency of the late 20thcentury warming trend appears unprecedented.