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Saarinen, T. 2003 (December): A 3000-year palaeoenvironmental record from annually laminated sediment of Lake Korttajärvi, central Finland. Boreas, Vol. 26, High-resolution physical analyses (varve thickness and relative X-ray density) were conducted on a 3000-year varved sediment sequence in Lake Korttajärvi, central Finland. Climate and the local environment strongly influence the properties of the lake sediments, and, through a combination of physical proxies, severe and favourable climate periods and anthropogenic effects on sedimentation with an annual to decadal resolution could be detected. We observed previously identified historical climate periods in the Lake Korttajärvi varve record. The Medieval Climate Anomaly (often termed the Medieval Warm Period) of AD 980-1250, which is characterized by highly organic sediment and a minor minerogenic flux during mild winters, started and terminated abruptly, but also included a short (30-year) colder period lasting between AD 1115 and AD 1145. The Little Ice Age, however, was not clear in our record, although there were two minor cooling periods in AD 1580-1630 and AD 1650-1710. Natural variability in the sediment record was disrupted by increased human impact in the catchment area at AD 1720. There is a distinct positive anomaly in mineral matter accumulation between 907 and 875 BC, which indicates more severe climate conditions. This period exists contemporary with a cold event, recorded worldwide, c. 2800 years ago.

A palaeomagnetic study of the Lake Nautajärvi sediment sequence in central Finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for Holocene stratigraphic correlation and age control. Based on x-ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the Lake Nautajärvi varve sequence, which covers nearly 10000 years with an estimated counting error of less than ±1% and a mean sedimentation rate of 0.66 mm yr-1. We reconstructed a record of the palaeomagnetic secular variation (PSV) of the Earth's magnetic field in this nearly 7 m long section of clastic-organic varves. Mineral magnetic measurements indicated that pseudosingle-domain magnetite is the major carrier of the remanence. PSV shows many of the familiar features of declination and inclination that have previously been recorded in northern Europe. In addition, the Lake Nautajärvi record contains a continuous record of relative palaeointensity.