Holocene fluctuations of cold climate in the Swiss Alps

Abstract

1. (1) This study deals with the vegetational history and climatic development of the Swiss Alps during the Holocene. Correlations with glacial readvancement in the Austrian Alps and the U.S.A. are discussed as well. 2. (2) The following pollen diagrams were established at the Botanical Institute of the University of Basel: three profiles from the ground of the former “Göscheneralp”, one from the mire of “Berg” near the artificial lake of Göscheneralp (Gotthard), and one from a 43 m deep bore made at “Val Frisal” (Vorderrhein). 3. (3) Radiocarbon dating, carried out by the 14C Laboratory at Berne produced the following, important results. Corylus avellana was abundant in Val Frisal prior to 6,700 years B.C. Abies alba had already spread from Tessin to Vorderrhein by about 6,000 years B.C. Picea abies spread from the east by 5,500 years B.C., at the latest (Zone V). The date for Corylus corresponds completely with results obtained in England, The Netherlands and in the Swiss Jura. However, Abies and Picea spread out in the valley of Vorderrhein at least 2,000 years earlier than in “Berner Oberland”. In all the profiles investigated it was found that Alnus viridis did not become prolific before the beginning of the Subboreal —at the earliest by about 3,000 years B.C. (Zone VIII). The two species, Rhododendron ferrugineum and R. hirsutum, existed in the Val Frisal up to the Late Boreal (Zone V). 4. (4) During the Holocene, the altitude of the timber line altered considerably. However, there is no evidence that the climatic conditions required by the forests were different during this time from those existing at present. The timber line was relatively high during the Boreal (Zone V), the early part of the Atlantic (Zone VII) and the Late Subboreal (Zone VIII). The reasons for its actual depression are diverse, and include both human activities and climatic changes which took place during the Late Holocene. 5. (5) The abundance of Corylus pollen grains near the basic moraine in Val Frisal proves that the innermost walls (Daun) were not left by the Weichselian ice before 7,000 years B.C. Consequently, the Preboreal (Zone IV) was a period of retardation in the subalpine-alpine region: the clear walls which dam up the upper basin of Frisal were deposited essentially later than in the Younger Dryas Time (Zone III). These clear walls originated on the boundary between Zones IV and V, and probably the classic “Daun Stadium” has to be included in this period. This palynological result has been well-confirmed by radiocarbon-dated wood from some places closely above the surface of the same basic moraine. The dating given was only about 6,500 years B.C. 6. (6) The Holocene warmth period was interrupted several times by strong fluctuations of cold climates. Some stages in the Swiss and Austrian Alps of lateral glaciers seem to have been caused by these fluctuations. The age of the “Misoxer Kaltphasen” corresponds to that of the Cochrane Readvance in North America (approx. 5,500-4,500 years B.C. in the Swiss Alps, and approx. 5,300 years B.C. in the U.S.A.). 7. (7) The Subboreal-Subatlantic boundary can be distinctly drawn, at Göschenneralp, between 900 and 800 years B.C. Furthermore, the beginning of the “Göschenen Kaltphase 1” is in full accordance with the Alaphah Mountain advance in Alaska. For further details and references, the reader is referred to Zoller 1966).