SYNCHRONOUS HOLOCENE CLIMATIC OSCILLATIONS RECORDED ON THE SWISS PLATEAU AND AT TIMBERLINE IN THE ALPS

Eight synchronous pre-Roman cold phases were found at 9600-9200, 8600- 8150, 7550-6900, 6600-6200, 5350-4900, 4600-4400, 3500-3200 and 2600-2 350 radiocarbon years BP by reconstructing past climate at two sites o n the Swiss Plateau and at timberline in the Alps. The cooling events during the early-and mid-Holocene represent temperature values similar to today, and apparently the onset of cooling events represents a dev iation from today's mean annual temperature of about 1 degrees C and i s triggered at a 1000-year periodicity. At Wallisellen-Langachermoos ( 440 m), a former oligotrophic lake near Zurich, the correlation betwee n summertime lake levels and the seed production of the amphi-Atlantic aquatic plant Najas flexilis was used to reconstruct lake levels over a 3000-year period during the first part of the Holocene. At Lake See dorf on the western Swiss Plateau (609 m) the sedimentological, palyno logical and macrofossil record revealed fluctuations of lake levels fo r the complete Holocene. From Lago Basso in the southern Alps (2250 m, Val San Giacomo near Splugen Pass, Northern Italy) the terrestrial pl ant macrofossils - especially Pinus cembra and Larix - allowed the rec onstruction of timberline fluctuations controlled by climate. A simila r climatic pattern was found at Gouille Rion pond in the central Swiss Alps (2343 m, Val d'Heremence) with plant macrofossils and pollen con centrations and percentages. We postulate that these climatic events a re detectable throughout central Europe by independent methods in comb ination with precise AMS-radiocarbon datings on terrestrial plant rema ins. Our data fit other proxy records of regional climatic change, suc h as cool intervals from Greenland ice cores, glacier movements in the Swiss and Austrian Alps, and dendro-densitometry on subfossil wood, a s well as the palaeoclimatic data from the Jura Mountains of France ob tained by sedimentological analyses. Thus our data indicate that the N orthern Hemisphere climate was less stable during the Holocene than pr eviously believed.