Biological and optical properties of Baltic surface waters and sea-land interaction – searching for interdependencies
Bielecka, L., Drozdowska, V., Złoch, I., Rak, D., Pelevin, V. V., Koltsova, E. M.
In June 2015, aboard the R/V Akademik Ioffe, surface waters of the Baltic Sea were studied along the Arkona Basin–Gulf of Gdańsk route, combining a 100 µm plankton net with remote (lidar) and in-situ (CTD and surface-microlayer) optical and physical measurements. Nineteen zooplankton taxa were recorded, with abundance ranging from 37,399 ind. m⁻³ in the Słupsk Furrow to 267,744 ind. m⁻³ in the Bornholm Basin and copepods dominating throughout. Fluorescence of surface-microlayer organic matter, indexed by the (M+T)/(A+C) fluorophore ratio, indicated a marine source west of the Słupsk Furrow and a terrestrial source to the east; lidar results likewise split the area into a western and an eastern bio-optical region. CDOM and FDOM concentrations correlated negatively with salinity, and zooplankton structure tracked the water's hydro-optical properties, pointing to sea–land interaction as the common control on the surface waters studied.