Little is known about the timing and the vegetation dynamics shortly after the Last Glacial Maximum (LGM) on the Swiss Plateau 19,000−15,000 cal B.P. Subsequent Late Glacial and Holocene vegetation changes are better known; however, it is unclear if the few available palynological and macrofossil records are able to capture the entire vegetation variability of the region. A new palaeoecological multiproxy study using pollen, spores, charcoal and X-ray fluorescence (XRF) from Burgäschisee (Swiss Plateau, 465 m a.s.l.) is used to reconstruct vegetation, fire and land use for the past 19,000 cal. years. Steppe tundra vegetation established at c. 18,700 cal B.P. only c. 300 years after the end of the LGM and deglaciation. A shift from steppe tundra (Artemisia, Helianthemum) to shrub tundra (Betula nana, Salix, Juniperus) with sporadic tree Betula stands occurred around 16,000 cal B.P., most likely in response to climate warming after the end of Heinrich event 1. Abundant spores of coprophilous fungi (Sporormiella, Cercophora) may reflect the presence of Pleistocene large herbivores (e.g. Mammuthus primigenius, Bison bonasus, Rangifer tarandus). Afforestation started more than 2,000 years later with Juniperus and tree Betula around 14,500 cal B.P. Mixed Betula and Pinus sylvestris forests persisted until the onset of the Holocene at 10,800 cal B.P., when mixed elm forests expanded into the region in response to climate warming. Around 8,200 cal B.P., mesophilous Fagus sylvatica and Abies alba partly replaced more heliophilous species in the forests, when climate became less continental and more moist. Pollen of Cerealia, Plantago lanceolata and other crops and weeds suggest that agricultural activities became significant during the Neolithic around 6,500 cal B.P. (4,550 cal B.C.). Archaeological findings from Neolithic pile dwellings around 5,950 cal B.P. (4,000 cal B.C.) indicate local settlements around the lake. The lake sediments are laminated for most of the last c. 6,800 years. With two independent proxies (XRF and pollen), we can demonstrate that these laminations are annual, suggesting short-term mixing of the lake water due to a more open landscape in response to land use. Our study shows that the annually laminated (varved) sediments from Burgäschisee have a great potential for high resolution multi-proxy analyses covering the past c. 6,800 years. They can provide accurate ages of cultural phases that might be compared with dendro-chronologically dated evidence from lake dwellings.

Compound-specific radiocarbon (14 C) analyses allow studying the fate of individual biomarkers in ecosystems. In lakes with small catchments, terrestrial biomarkers have the potential to be used for the dating of sediments that lack the traditionally targeted terrestrial macrofossils, if the specific organic compounds are deposited soon after production. On the other hand, if the biomarkers have been stored for a significant amount of time in the soils of the catchment before transported to the lake, their age can be used to reconstruct changes in average residence time of organic material on land through time. Here we present a study based on compound-specific 14 C analysis of the sedimentary record of Lake Soppensee, Switzerland, targeting long-chain n-alkanes of exclusive terrigenous origin, and comparing them with sediment ages obtained by high-resolution macrofossil dating. Additionally, we measured 14 C ages of bulk organic matter and carbonate samples to assess the hard water effect. Prior to 3100 cal BP n-alkanes had about the same age as the sediment or they were slightly older, indicating that the vast majority of the terrestrial organic carbon transported to the lake had a short residence time on land. In the samples younger than 3100 cal BP an increasing offset is observed, indicating liberation of old buried soil organic matter that must have accumulated over the previous millennia.

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