Search

On the basis of sediment and pollen analyses of a radiocarbon-dated sediment sequence from Lake Joux in the Swiss Jura Mountains (west-central Europe), this paper presents a high-resolution record of lake-level and vegetation changes for the last millennium. The lake-level record makes it possible to determine that lowstands of the water-table dominated at c. AD 1200-1400, and from 1720 onward, with interruptions by short-lived rise events at c. AD 1340 and 1840. Highstands prevailed at c. AD 1100, and around AD 1450, 1550 and 1700. The comparison of the Joux lake-level record with a solar irradiance record based on cosmogenic nucleides supports the hypothesis of a major solar forcing of climate variations in west-central Europe over the last millennium. In agreement with other palaeohydrological records established in Western Europe and in the central North Atlantic Ocean, the Joux lake-level record suggests that, on a multicentennial scale, the period of the 'Little Ice Age' coincided in the European mid-latitudes with wetter climatic conditions, and probably with an increase in summer precipitation. Variations in the hydrological cycle appear to have been associated with changes in the general atmospheric circulation pattern, probably coupled with variations in oceanic circulation and solar activity. The Joux record also points to changes in water resources expected to result from ongoing global warming. Finally, despite the severe climatic conditions which prevail in the Joux Valley, the human impact history at Lake Joux over the last millennium seems to reflect political choices and economic context more than climatic changes. [ABSTRACT FROM AUTHOR]

The pollen content of three adjacent peat profiles has been analysed to study the development of pasture woodland in the small valley Combe des Amburnex (1300 m a.s.l.). Chronostratigraphy based on lowland pollen assemblages and radiocarbon dates was used to correlate and date the profiles. Forest and mire grazing occurred throughout at least the past two millennia. Before the ninth century the forest consisted of about equal parts of Abies, Fagus and Picea. Thereafter Picea increased and is today strongly dominant in the area, likely an effect of selective browsing. The central part of the valley obtained its modern structure of pastures and forests in the twelfth century, and the pasture woodland in general came into existence during the seventeenth century as an effect of extensive fire activity, possibly charcoal production. In the twentieth century grass and nutrient-demanding species increased relative to other herbs. [ABSTRACT FROM AUTHOR]