High-resolution record of environmental changes during Boreal (Eemian) transgression from the northeastern White Sea Region

<p>In relation to the overall importance of reconstructing interglacial marine environments and water mass evolution in subpolar and polar northern regions we carried out a high-resolution investigation of a 4.5 m thick sediment sequence of the Boreal (Eemian) marine beds directly overlying Moscovian (Saalian) till in the northeastern White Sea Region. The obtained sediments samples allow for a detailed evaluation of past events on the basis of changes in lithology, microfossils (foraminifers, ostracods, pollen, aquatic palynomorphs) and benthic foraminiferal isotope data (&#948;¹⁸O, &#948;¹³C).</p><p>The early stage of inundation is featured by accumulation of marine clays overlying the till and stands out as a period of harsh, fluvially-affected environmental conditions with cold turbid waters and heavy seasonal sea-ice cover. The abundance of freshwater chlorococcalean algae <em>Botryococcus </em>cf.<em> braunii </em>in the basal part of marine clays right above the till indicates a significant influence of local river runoff at the beginning of inundation, whereas dinocyst assemblage dominated by <em>Islandinium </em>var.<em> minutum</em> reflects harsh and severe marine conditions. Dwarf birches occupied the coast at the onset of inundation, and subsequently gave way to pine-birch forest tundra.</p><p>Further climate amelioration and increasing influence of saline and warm open-sea waters correspond to accumulation of silts and sands of the middle part of the section. These are evidenced by a sharp increase in &#948;18O values as well as the overall abundance and diversity of microfossils. The microfossil assemblage in the middle part of the section is characterized by a high percentage of foraminifers characteristic of the Arctic shelves with high seasonal productivity (<em>Islandiella </em>spp., <em>Nonion labradoricum</em>), occurrence of relatively deep-water Arctic species among foraminifers (<em>Melonis barleeanus</em>) and ostracods (<em>Krithe glacialis</em>), as well as sporadic presence of <em>Penthapharsodinium dalei</em>, <em>Spiniferites</em> cf. <em>pachydermus</em> and <em>Nematosphaeropsis labyrintus </em>among cysts of dinoflagellates. The drastically increased share of pollen of woody plants from mixed dark coniferous-deciduous forest belt indicates forest expansion around sea basin due to more humid and warm climate conditions.</p><p>The final regressive stage, which was caused by isostatic crustal rebound, witnessed the accumulation of sands and gradual decrease of taxonomic diversity and abundance of microfossils, growing proportion of relatively warm-water and shallow-water species especially among ostracods (<em>Finmarchinella finmarchica, Patagonicythere dubia, Cythere lutea, Hemicytherura clathrata)</em>. However, there is no direct indication among the microfossil community for enhanced penetration of warm Atlantic waters. The spore-pollen data testify to the climate deterioration and the absence of thermophylic species in the forest stands. &#160;</p><p>This research was supported by the Russian Science Foundation, project 22-27-00324.</p><p>&#160;</p>