Recent paleolimnological studies of the small lakes sediments in the northern Karelian Isthmus have demonstrated that the beginning of organic (gyttja) sedimentation in the Holocene was not simultaneous due to the differences in 1) the lake’s elevation, and 2) the proximity to the Lake Ladoga shoreline. Organic sedimentation in the lakes located at 30 m a.s.l. and higher started around 11000 cal. BP. No major changes in their hydrological conditions have been recorded hereafter. In the lowland lakes (11-20 m a.s.l.) located near the Lake Ladoga shoreline the beginning of organic sedimentation has been dated to 3000-4000 cal. BP. The underlying clayey gyttja contains lower amount of organic matter (10 %) with predominant diatom assemblages typical for Lake Ladoga. Therefore, the rapid increase in organic content in the lake sediments points at the isolation from Lake Ladoga, and enables to date the termination of the Ladoga transgression to 3000-4000 cal. BP. In the lakes situated at 11-14 m a.s.l. near the present watershed between the Gulf of Finland and Lake Ladoga, gyttja accumulation commenced at 3000-4000 cal. BP. Here the organic sediments overlie unsorted sand and silt that contain “large- lake” diatom taxa. Such sedimentary succession indicates that high-energy sedimentary environments (strait or river-like outlet from Lake Ladoga) persisted in the northern Karelian Isthmus until at least 4000 cal. BP when low-energy environments established resulted from Lake Ladoga regression. Hence, the small-lakes sedimentary records provide an independent evidence for the Lake Ladoga - Baltic Sea connection through the main Ladoga outlet in the north of the Karelian Isthmus in the mid-Holocene.
Recent palaeolomnological studies of the small lakes sediments in the northern Karelian Isthmus have demonstrated that the start of organic (gyttja) sedimentation in the Holocene was not simultaneous due to the differences in 1) the lake's elevation, and 2) the proximity to Lake Ladoga shoreline. Organic sedimentation in the lakes located at30 ma.s.l. and higher started around 11000 cal. BP. No major changes in their hydrological conditions have been recorded hereafter. In the lowland lakes (11-20 ma.s.l.) located in the proximity of the Lake Ladoga shoreline the start of organic sedimentation has been dated to 3000-4000 cal. BP. The underlying clayey gyttja contains lower amount of organic matter (ca 10 %) and the diatom assemblages dominated by the “large-lake” diatoms typical for Lake Ladoga. Therefore, the rapid increase in organic content in the lake sediments points at the isolation from Lake Ladoga, and enables to date the termination of the Ladoga transgression to 3000-4000 cal. BP. In the lakes situated at 11-14 ma.s.l. near the present watershed between the Gulf of Finland and Lake Ladoga, gyttja accumulation commenced at 3000-4000 cal. BP. Here the organic sediments overlie unsorted sand and silt that contain “large-lake” diatom taxa. Such sedimentary succession indicates that high-energy sedimentary environments (strait or river-like outlet from Lake Ladoga) persisted in the northern Karelian Isthmus until at least 4000 cal. BP when low-energy environments established resulted from Lake Ladoga regression. Hence, the small-lakes sedimentary records provide an independent evidence for the Lake Ladoga – Baltic Sea connection through the main Ladoga outlet in the north of the Karelian Isthmus in the mid-Holocene.
The authors declare that there are no conflicts of interest present.