Late‐glacial and early Holocene changes in vegetation and lake‐level at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland)

Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges-Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake-level during the Bolling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophae zone (regional pollen assemblage zone (RPAZ) CHb-2, first part of the Bolling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake-level. A weak rise occurred during this zone. The Juniperus–Hippophae to Betula zone transition coincided with a lake-level lowering, interrupted by a short-lived but marked phase of higher lake-level recorded at the neighbouring site of Hauterive-Champreveyres, but not present at Hauterive/Rouges-Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb-3, second part of the Bolling, ca 14 450–14 000 cal. yr BP), a marked rise in lake-level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake-level associated with raised values in Artemisia and other non-arboreal pollen. The last part of RPAZ CHb-3 saw a fall in lake-level. The lower lake-levels during RPAZ CHb-2 to early RPAZ CHb-3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake-level punctuating the GI 1e might be linked to the so-called Intra-Bolling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen-isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges-Terres lake-level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb-4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb-4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake-levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges-Terres lake-level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 14C yr BP corresponded to periods of generally lower lake-level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley & Sons, Ltd.