Lakes provide a key to the past. They form important climate archives, also in alpine regions. Lakes ideal for palaeoclimatic studies show the following characteristics:

• Continuous, long-term environmental record (thousands to million of years)
• High temporal resolution: Varves (annual layers) can even provide a seasonal resolution.
• High sensitivity to climate change: Lakes record changes in their environment in the sediments.
• Wide geographic and environmental distribution over all latitudes (e.g. ice cores are limited to polar regions and high-altitude ice caps, tree rings are time-limited and most useful across temperate latitudes)
• Variety of information: Lake sediments often record information in a variety of components that indirectly represent the atmosphere (precipitation, seasonality, temperature, variability, wind, storms, drought), the terrestrial ecosystem (pollen, insects, other fossils, volcani ash, flood recurrence, etc.) or the aqueous system (salinity, evaporation, etc.).
• Comparability over time: Lacustrine sediments can often be compared to their modern counterparts in the same lake, which in turn can be compared to historical and instrumental records for the calibration of climate signals.
   

Sedimentation processes in lakes

Cores consist of sediments deposited over long periods of time. Hence, they provide evidence of changing processes in the catchment and the region (see figure 1).

Clastic input: Debris from slopes, particles from volcanic eruptions, etc. Clastic input may give indications about storm events, natural disasters, humid or dry periods, etc.

Biological input: Pollen and plant macrorests indicate the former vegetation.

Chemical input: Ions precipitate out of the saturated lake water, e.g. calcite.

Human impact is e.g. given by fertilizers (causing high eutrophication and therefore algal production), industrial pollutants, erosion due to agriculture or solid waste.

1 - Overview of sedimentation processes

29 August 2011
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