THE BOREAL TRANSGRESSION IN NORTHERN RUSSIA

During the Eemian the North Russian lowland from Kola in the west to Taymyr in the east was transformed into a shallow shelf sea. In major river basins the “Boreal Transgression” penetrated up to 800 km from the present coastline, and the marine sediments exposed along rivers and coasts have been studied for more than 150 years, not least because of their rich marine faunas with boreal species, which now have their northern limits along the Norwegian coast, but occurred as far east as Taymyr, more than 3000 km to the east.

Results from the QUEEN and BALTEEM projects show that the transgression began after the onset of the Eemian and peaked c. 1500 yr into the interglacial. After this, regression set in but major rivers existed as estuaries for another 5000 yr. Micro- and macropalaeontogy show maximum temperatures and salinities in the Early Eemian, followed by a drop in salinity and establishment of a distinct halocline with cold arctic fauna below low saline warm surface water.

For some millennia during the peak transgression the watershed between the White Sea and the Baltic was breached, and a seaway through Karelia connected the Barents and North Seas. However, both previous and our studies show that the seaway was restricted by thresholds in both ends and never functioned as a corridor for major oceanic exchange. Its faunas were low diverse, dominated by the arctic Portlandia arctica, which penetrated further to the south than during the Holocene. At the same time warm extralimital species lived both to the north and south of the seaway.

Although the north Russian lowlands have been inundated by the sea several times during the Quaternary, the Eemian inundation was the most extensive for at least 1 ma. The transgression did not follow the retreating ice, but began in the warm interglacial. The main cause for this singular event was probably the unprecedented high rate of eustatic sea level rise at the opening of the Eemian, which for some time outdid the isostatic rebound after the Saalian ice sheet. This implies that the melting of the Saalian ice sheet in Eurasia was leading the global rhythm. The widespread warm boreal molluscs in the Early Eemian are explained by a more vigourous North Atlantic Drift sending abundant warm saline water north along the European coasts and into the Barents and Kara Seas.