Table 1. Tree growth index and reconstructed precipitation series from 515 BC to AD 1993 based on the archaeological and living tree ring datasets from Dulan and Shenge, China

Annual precipitation for the last 2,500 years was reconstructed for northeastern Qinghai from living and archaeological juniper trees. A dominant feature of the precipitation of this area is a high degree of variability in mean rainfall at annual, decadal, and centennial scales, with many wet and dry periods that are corroborated by other paleoclimatic indicators. Reconstructed values of annual precipitation vary mostly from 100 to 300 mm and thus are no different from the modern instrumental record in Dulan. However, relatively dry years with below-average precipitation occurred more frequently in the past than in the present. Periods of relatively dry years occurred during 74-25 BC, AD 51-375, 426-500, 526-575, 626-700, 1100-1225, 1251-1325, 1451-1525, 1651-1750 and 1801-1825. Periods with a relatively wet climate occurred during AD 376-425, 576-625, 951-1050, 1351-1375, 1551-1600 and the present. This variability is probably related to latitudinal positions of winter frontal storms. Another key feature of precipitation in this area is an apparently direct relationship between interannual variability in rainfall with temperature, whereby increased warming in the future might lead to increased flooding and droughts. Such increased climatic variability might then impact human societies of the area, much as the climate has done for the past 2,500 years.

Geochemistry, carbon isotope ratio and radiocarbon ages of sediment core GIK1093-2 from Bornholm Basin, Baltic Sea

Concentrations of Cd, Pb, Zn, Cu, Co, Ni, Fe, and Al203, water content, the amounts of organic carbon, the ratio of 13C/12C and the 14C-activity of the organic fraction were determined with sediment depth from a 34 cm long box-core from the Bornholm Basin (Baltic Sea). The average sedimentation rate was 2.4 mm/yr. The upper portion of the core contained increasing amounts of 14C-inactive organic carbon, and above 3 cm depth, man-made 14C from atomic bomb tests. The concentrations of the heavy metals Cd, Pb, Zn, and Cu increase strongly towards the surface, while other metals, as Fe, Ni and Co remain almost unchanged. This phenomenon is attributed to anthropogenic influences. A comparison of the Kieler Bucht, the Bornholm and the Gotland Basins shows that today the anthropogenic addition of Zn is about 100 mg/m**2 yr in all three basins. The beginning of this excess of Zn, however, is delayed by about 20 years in, the Bornholm Basin and by about 40 years in the Gotland Basin. It is suggested that SW-NE transport of these anthropogenically mobilized metals may be related to periodic bottom water renewal in the Baltic Sea sedimentary basins.