Holocene climate variability in Europe: Evidence from delta O-18, textural and extension-rate variations in three speleothems

Time-series O isotope profiles for three U-Th dated stalagmites have revealed that for much of the Holocene, a site on the Atlantic seaboard (SW Ireland) exhibits first-order delta(18)O trends that are almost exactly out of phase with coupled delta(18)O curves from two southern European sites (SE France and NW Italy). In the Irish stalagmite (CC3 from Crag Cave, SW Ireland), low delta(18)O at 10,000 cal yr BP reflects cool conditions. By the early to mid-Holocene (9000- 6000 cal yr BP)delta(18)O had increased, reflecting the onset of warmer conditions on the Atlantic seaboard. This shift to higher delta(18)O was accompanied by a marked increase in the stalagmite extension rate, reinforcing our interpretation that this was a period of relative warmth. Except for an episode of increased extension rare about 5500 yr ago, delta(18)O in the Crag stalagmite exhibits a gradual decrease, accompanied by declining extension rates between 7800 and 3500 cal yr BP, interpreted as a cooling trend. There is evidence for increases in both delta(18)O and stalagmite extension rate in the period from 3500 cal yr BP to the present day suggesting a return to warmer conditions on the Atlantic seaboard. In the stalagmite from NW Italy (ER76, Grotta di Ernesto, Trentino province) the early-Holacene (c. 9200-7800 cal yr BP) is characterised by high delta(18)O, probably indicative of warm and/or dry conditions. Exceptionally low delta(18)O from 7800 to 6900 cal yr BP at this site reflects a well-defined wet phase (Cerin wet phase). In the last three millennia, this stalagmite exhibits a shift to lower delta(18)O, interpreted as some combination of cooler and/or wetter conditions. Unlike the Irish stalagmite, the Italian sample does not show a correlation between delta(18)O and extension rare. Instead, its extension rate correlates roughly with delta(13)C, presumably reflecting a climate-driven vegetation change, In the early Holocene, delta(18)O in the French stalagmite (CL26, Grotte de Clamouse, Herault province, SE France) was low relative to its Holocene average. For much of the period since c, 3500 cal yr BP this stalagmite exhibits higher delta(18)O than in the early Holocene, suggesting warmer conditions. Like the Irish stalagmite, the French sample exhibits a well-defined correlation between delta(18)O and extension rate, Had drip-water availability been the dominant control on delta(18)O at this semi-arid site then higher delta(18)O would have been accompanied by lower, not higher extension rates. This suggests strongly that temperature rather than rainfall amount was the dominant control at this site. While conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early Holocene warm conditions on the Atlantic seaboard (Irish site) coincided with relatively cool conditions at the Clamouse site. By c, 3500 yr ago the pattern appears to have been reversed. (C) 1999 Elsevier Science Ltd. All rights reserved.