title: Solar and atmospheric forcing on mountain lakes.
abstract: We investigated the influence of long-term external forcing on aquatic communities in Alpine lakes. Fossil microcrustacean (Cladocera) and macrobenthos (Chironomidae) community variability in four Austrian high-altitude lakes, determined as ultra-sensitive to climate change, were compared against records of air temperature, North Atlantic Oscillation (NAO) and solar forcing over the past ~400years. Summer temperature variability affected both aquatic invertebrate groups in all study sites. The influence of NAO and solar forcing on aquatic invertebrates was also significant in the lakes except in the less transparent lake known to have remained uniformly cold during the past centuries due to summertime snowmelt input. The results suggest that external forcing plays an important role in these pristine ecosystems through their impacts on limnology of the lakes. Not only does the air temperature variability influence the communities but also larger-scale external factors related to atmospheric circulation patterns and solar activity cause long-term changes in high-altitude aquatic ecosystems, through their connections to hydroclimatic conditions and light environment. These findings are important in the assessment of climate change impacts on aquatic ecosystems and in greater understanding of the consequences of external forcing on lake ontogeny.
authors.affiliation: University of Helsinki, Department of Geosciences and Geography, Division of Geology and Geochemistry, P.O. Box 64, FI-00014 University of Helsinki, Finland; University of Jyvaskyla, Department of Biological and Environmental Science, Division of Aquatic Sciences, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland; University of Innsbruck, Research Institute for Limnology, Mondseestrasse 9, A-5310 Mondsee, Austria. Electronic address: tomi.luoto@helsinki.fi.
authors.forename: Tomi P
authors.initials: TP
authors.lastname: Luoto
authors.affiliation: University of Jyvaskyla, Department of Biological and Environmental Science, Division of Aquatic Sciences, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland; University of Innsbruck, Research Institute for Limnology, Mondseestrasse 9, A-5310 Mondsee, Austria.
authors.forename: Liisa
authors.initials: L
authors.lastname: Nevalainen
keywords: Aquatic ecology; Chironomidae; Cladocera; Climate change impacts; Global change; Paleolimnology