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The reasons for relative sea level (RSL) changes in the Baltic Sea basin are the glacio-isostatic land uplift and the eustatic movement of the ocean level. The drop in RSL has been the dominant feature of the Holocene shoreline displacement in most of the Baltic basin, except for relatively short periods of transgressions during the Ancylus Lake and Litorina Sea stages.
The Holocene relative sea level changes were investigated in Loviisa area, where the present apparent land uplift rate varies from 2 to 2.5 mm/yr. The investigated 13 isolation basins are located between 1.1 and 29.7 m above present sea level. The methods employed were lithostratigraphic interpretation, diatom analyses and radiocarbon dating (26 conventional and 2 AMS).
The uppermost basin (Lake Pitkajarvi) became isolated from freshwater Baltic Sea basin c. 9000 cal. yr BP, and after that is has been remained as an independent small lake basin. Lake Ryttarjarvi (26.5 m a.s.l.) was also became isolated from freshwater Baltic Sea basin c. 8800 cal. yr BP, but the marine (Litorina) transgression crossed the threshold altitude of the basin c. 8300 cal. yr BP. The reason for this transgression was the global sea level rise, which exceeded the rate of uplift in the study area. However, land uplift rate and sea level rise were almost in balance in this area, as results indicate the amplitude of around one metre for the transgression. The sea level curve for the Loviisa area both indicates a relatively regular uplift and an overall relative sea level lowering during the last 6000 years.
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