2020 Issue №4

The article is aimed at reconstructing the paleoecological conditions in the Gdansk Basin of the Baltic Sea in the Late Holocene. The hydrological and hydrochemical conditions of its isolated bottom layer are strongly influenced by water exchange with the North Sea, which in connected to the World Ocean. Information on environmental conditions in the past is necessary to understand the observed changes in the Baltic Sea ecosystem, to identify the natural and anthropogenic components of these changes, as well as to make re­liable forecasts. Changes in natural conditions are reflected in the composition of bottom sediments. Based on the complex study of three short sediment cores, including lithological, micropaleontological and geochemical analysis, the environmental conditions in the Gdansk basin in the Post-Litorina stage of the Baltic Sea were reconstructed. According to the correlation of sediment analysis data with published reconstruction results, the sediments of the stud­ied cores were formed during the last three millennia (from the Roman Warm Pe­riod to the Modern Warm Period). Intensified water exchange between the Baltic and North Seas was recorded before the Roman Warm Period, during the Roman Warm Period itself, the Dark Ages and during the Medieval Cli­mate Optimum. Periods of climate warming, characterized by an increase in surface water productivity and bottom water hypoxia, correspond to the Ro­man Warm Period, the Medieval Climatic Optimum, and the Modern Warm Period.

The study focuses on chlorophyll "a"concentration variability in the South-Eastern part of the Baltic sea in summer 2018. The data of the MODIS radiometer installed on Aqua and Terra satellites were used for the analysis. The average concentration of chlorophyll "a" in the warm period of 2018 (May-August) was 3.8 mg/m3 while the average sea surface temperature was 17.7° С. The Maximum concentration of chlorophyll "a" (8.1 mg/m3) was rec­orded in May. However, the most massive development of phytoplankton oc­curred in July — the average monthly concentration of chlorophyll "a" was the highest and exceeded 4.2 mg/m3. August was the warmest month, when the peak sea surface temperature (24.7° С) was observed, and the average monthly temperature reached 21.8° С, which is higher than the average annu­al value for August (2.8° С). Thus chlorophyll "a" concentration for the peri­od under study was revealed at the average multiyear level, and the sea sur­face temperature was higher than the average for 2003—2016 by 2.4° С. The direct influence of the weather anomaly of 2018, which caused the water warming above the long-term average level, on the monthly average concen­trations of chlorophyll “a” was not revealed, that indicates a sustainable state and strength of the south-eastern Baltic Sea ecosystem towards the variability of environmental conditions over several years.