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This paper examines tree-ring width and δ13C chronologies from a network of five Iberian pine forests to determine their sensitivity to climate variability under different site conditions. Interseries comparisons revealed better and more homogenous agreement among δ13C records than among tree-ring width series of the different sites. This suggests that δ13C ratios may preferentially record large-scale climatic signals, whereas ring-width variations may reflect more local factors. A negative relationship was found between ring-width and δ13C. As inferred from response function analyses, ring-width and δ13C showed significant relationships with climate. The analyses of different sites and species revealed unshared tree-ring width responses to summer temperature and precipitation, whereas all δ13C series were highly sensitive to current year summer precipitation and, to a lesser extent, to current summer temperature. A strong summer precipitation signal seems to dominate the δ13C of trees growing under Mediterranean climate, even when the mean climatic site conditions do not indicate distinct summer drought. Therefore, δ13C values reflect precipitation variability during the summer season better than tree-ring widths. This demonstrates that δ13C from tree-rings can be a very useful tool for climatic reconstruction in the Mediterranean region, especially when climate-growth relationships are weak. [ABSTRACT FROM AUTHOR]

Nearly 13,000 years ago, the warming trend into the Holocene was sharply interrupted by a reversal to near glacial conditions. Climatic causes and ecological consequences of the Younger Dryas (YD) have been extensively studied, however proxy archives from the Mediterranean basin capturing this period are scarce and do not provide annual resolution. Here, we report a hydroclimatic reconstruction from stable isotopes (δ 18 O, δ 13 C) in subfossil pines from southern France. Growing before and during the transition period into the YD (12 900-12 600 cal BP), the trees provide an annually resolved, continuous sequence of atmospheric change. Isotopic signature of tree sourcewater (δ 18 O sw ) and estimates of relative air humidity were reconstructed as a proxy for variations in air mass origin and precipitation regime. We find a distinct increase in inter-annual variability of sourcewater isotopes (δ 18 O sw ), with three major downturn phases of increasing magnitude beginning at 12 740 cal BP. The observed variation most likely results from an amplified intensity of North Atlantic (low δ 18 O sw ) versus Mediterranean (high δ 18 O sw ) precipitation. This marked pattern of climate variability is not seen in records from higher latitudes and is likely a consequence of atmospheric circulation oscillations at the margin of the southward moving polar front.