Spectrofluorometric characteristics of fluorescent dissolved organic matter in a surface microlayer in the Southern Baltic coastal waters

Abstract

This paper presents results of characterization of Dissolved Organic Matter (DOM) using fluorescence spectroscopy in the surface microlayers (SML) and subsurface layers (SS) in the Baltic Sea. Samples for spectroscopic measurements were collected during five research cruises in April/May and October 2013 and 2014 in a surface microlayer and a subsurface layer at a depth of 1 m along two transects from the river outlets to the open sea. The first transect was located from the Vistula River outlet to the Gdańsk Deep and the second transect was located from the Łeba River outlet to Słupsk Furrow. Results indicated that DOM fluorescence intensity in the SML is higher by 20% compared to the SS. The Humification Index, HIX values were lower in SML than SS by 13%. That indicates that SML is depleted in molecules with high molecular weight and higher aromaticy. The inverse relationship of fluorescence intensity of dominant peaks with salinity both in SML and SS suggests that FDOM variability is regulated mostly by terrestrial DOM input.