The fluorescence and absorption measurements of the samples collected from a surface microlayer 10 (SML) and a subsurface layer (SS), a depth of 1 m were studied during three research cruises in the Baltic Sea along with hydrophysical studies and meteorological observations. Several absorption (E 2 :E 3 , S, S R ) and fluorescence (fluorescence intensities at peaks: A, C, M, T, the ratio (M+T)/(A+C), HIX) indices of colored and fluorescent organic matter (CDOM and FDOM) helped to describe the changes in molecular size and weight as well as in composition of organic matter. The investigation allow to assess a decrease in the 15 contribution of two terrestrial components (A and C) with increasing salinity (~1.64% and ~1.89 % in SML and ~0.78% and ~0.71 % in SS, respectively) and an increase of in-situ produced components (M and T) with salinity (~0.52% and ~2.83% in SML and ~0.98% and ~1.87% in SS, respectively). Hence, a component T reveals the biggest relative changes along the transect from the Vistula River outlet to Gdansk Deep, both in SML and SS, however an increase was higher in SML than in SS (~18.5% and ~12.3%, 20 respectively). The ratio E 2 :E 3 points to greater changes in a molecular weight of CDOM affected by a higher rate of photobleaching in SML. HIX index reflects a more advanced stage of humification and condensation processes in SS. Finally, the results reveal a higher rate of degradation processes occurring in SML than in SS. Thus, the specific physical properties of surface active organic molecules (surfactants) may modify, in a specific way, the solar light spectrum entering the sea and a penetration depth of the solar radiation. Research 25 on the influence of surfactants on the physical processes linked to the sea surface become an important task, especially in coastal waters and in vicinity of the river mouths.
1.30 measurably different from the underlying water due to the molecules forming SML, called surfactants (Soloviev and Lukas, 2006;Liss and Duce, 2005). Sea surface films are created by organic matter from sea and land sources: (i) dissolved and suspended products of marine plankton contained in seawater, (ii) terrestrial organic matter that enter seawater from a land (natural and synthetic) and (iii) oil products from leakages of the sea-bottom. Surface films dissipate due to loss of material at the sea surface, including 35 microbial degradation, chemical and photo chemical processes, as well as due to absorption and adsorption Ocean Sci. Discuss.,