Late Holocene environmental changes recorded at Ghetarul de la Focul Viu, Bihor Mts, Romania

Complete text of publication follows. A significant number of ice caves in temperate climatic region contain ice and wood remnants from same site and probably same time span. Ghetarul de la Focul Viu is located in the Bihor Mts. (46.27 deg N , 22.68 deg E) approximately 50 kilometres far from Cluj (Romania). A 772 cm long ice core was extracted in November 2001 from the ice or of the Main Chamber. At the depth of 6.67 meters of the ice core a piece of wood appeared. In addition, a branch outcropping from the ice block at its sidewall at 11.1 meters depth was also sampled. Both wood remnants were undergone radiocarbon age determination. In February of 2002 we have collected ice samples for tritium measurements. This paper synthesizes the isotope and tree-ring data gathered at Focul Viu Ice Cave. The oxygen isotope compositions were analysed in the Institute for Geochemical Research, Hungarian Academy of Sciences (Budapest). Radiocarbon dates of wood samples were determined by gas proportional counting and the tritium content of the water samples were determined by the 3He-ingrowth method in the Institute of the Nuclear Research of the Hungarian Academy of Sciences (Debrecen). We have found a correspondence between the impurity layers of the ice block, δ18O data of the shallow ice core and standardized ring width curve of a conifer species. The 850 ± 50 year BP radiocarbon age (1160-1260 cal AD) from 6.67 m depth of ice indicate, that the stable isotope data of the 7 metres long ice core origin approx. from the past 800-900 years. However, melt events introduce obvious hiatuses in the sequence. The response function analysis revealed that main growth influencing climate factors for Abies alba are June mean temperature and early summer water supply. The sufficiently represented part of the 420 year long tree-ring index curve suggests particular periods unfavourable to annual increment of the firs. Decades unfavourable for fir growth are 2000-1980, 1940-1920, 1890-1870, 1860-1820, while the favourable periods are 1980-1940, 1920-1890, 1870-1860. The fit between the growth favourable decades and the muddy layer concentrations seems to be a promising dating method of the ancient melting events and fragmentally remained ice bands. Previously negative intervals of Easton coefficient time series were fitted to ice accumulating periods. The independent dating methods - Easton coefficient and fir index - show similarity back to 1730 for ice accumulation and melting periods. (author)