The postglacial history of Kitkajärvi, North-eastern Finland, as indicated by trend-surface analysis and radio-carbon dating

The Kitka lake complex (Kitkajärvi), some 300 km2 in total area, is located at an altitude of 240.2 m a.s.l. on the Maanselkä watershed. Its waters flow eastwards to the White Sea via the river Kitkajoki. The western parts of the lake basin in particular feature shores now situated on dry land. The clearest raised shore‑line represents a phase of Kitkajärvi called here Early Kitka. The postglacial history of the lake complex is studied here by means of trend‑surface analysis and a combination of pollen stratigraphy with radio‑carbon dating. The area is shown to have undergone deglaciation around 9400–9500 B. P. and to have been supra‑aquatic from the outset. The Early Kitka shore‑line now slopes from west to east with a gradient of approx. 0.2 m/km. At this early phase the lake possessed bifurcation features, having one outflow channel eastwards via Kitkajoki and another westwards into the Gulf of Bothnia via Livojärvi. This latter route, which most probably existed immediately on deglaciation, was closed around 8400 B. P. A gradient curve for the Kitka region is presented based on dated shore­lines, and this suggests an exponential decrease in shore level gradients towards the present day