CLASS

Cold season climate reconstructions from Lakes in the Alpine regions of Switzerland and Sweden

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 Obiettivo del progetto (Objective)

'Past variations in interannual climatic variability are currently not well understood, mainly due to a lack of temperature reconstructions for the winter season. This proposal aims to provide quantitative data on winter-spring temperatures for two lake sites in the Alpine regions of Switzerland and northern Sweden, since these are likely to contain sensitive archives of past climate change. The reconstruction of winter temperatures in these two regions is highly relevant, since local winter temperatures and precipitation are controlled by the variability and strength of the North Atlantic Oscillation (NAO). Increased knowledge on the impact of NAO in these sensitive mountain regions is crucial for a better understanding of future impacts on e.g. lake ecology, water-and energy supplies and winter tourism. In addition, obtained data can be compared to existing summer temperature reconstructions to study changes in interannual variability. A novel methodology developed at the host institute is proposed, using Chrysophyte stomatocysts as a proxy for winter-spring temperatures. However, to distinguish between climate-induced changes in stomatocyst assemblages and the impact of other factors affecting lake ecology, such as human influence, a multi-proxy approach is required including the analysis of pollen, C and N ratios, total biogenic silica and sediment grainsize. At the Swiss site the proposal targets three time periods; I) modern time (AD 1864-present), for validation with measurement data, II) the most intense phase of the Little Ice Age, including the Maunder Minimum (AD 1650-1800) and III) the warmest phase of the Mediaeval Warm Anomaly (a 100 years window, possibly AD 850-950). In Sweden the proposed method has not been applied before, and therefore the method will be tested her for the calibration period, AD 1913-present.'

Introduzione (Teaser)

The effect of global warming on Europe?s fragile mountain ecosystems is now better understood thanks to the work of the EU-backed CLASS project. The initiative has reconstructed past winter temperatures in the Alpine regions of Switzerland and Sweden.

Descrizione progetto (Article)

Improved knowledge of environmental changes enables scientists to better understand the impacts on lake ecology, water and hydro-electric supplies, and winter tourism. Furthermore, data obtained can be compared with existing reconstructions of summer temperatures to investigate changes in yearly temperature variability.

Researchers in the CLASS project have sampled two lakes; one based in the Swiss alps and the other in central Sweden. Scientists at the Swiss site focused on the last 1 000 years, comparing a particularly warm period known as the ?Medieval warm anomaly? and a cool period called the ?Little ice age?. Results from the Swedish site were limited to the period AD 1946-2005 and compared in detail with meteorological data.

Reconstructions were achieved with the aid of Chryosphyte algae, which produce silicon-based objects known as stomatocysts. The stomatocysts are retained in lake deposits and can be studied in detail using a scanning electron microscope. The algae are known to be sensitive to the break up of lake ice, which correlates with average October to April air temperatures.

The CLASS consortium has successfully created a method for cold-season climate reconstructions. This has provided unique insight into a range of climatic parameters including long- and short-term temperature variability. The project?s findings reveal a strong link with ocean current circulation patterns, known as the North Atlantic Oscillation (NAO), which control local winter temperatures and precipitation.

Increased knowledge of the impact of the NAO on sensitive mountain regions across Europe will help policy-makers and scientists to prepare for future climate changes. They will then be in a position to take the best course of action in an attempt to mitigate their effects.