Sources and composition of particulate organic carbon in the Baltic Sea: The use of plant pigments and lignin-phenols as biomarkers

Abstract

Water samples were collected in the Baltic Sea, along a north to south transect that extended from Bothnian Bay to the Baltic proper, in July 1994-just after the period of peak freshwater discharge. Plant pigments and lignin-phenols were used as biomarkers to determine the dominant sources of phytoplankton and terrestrial inputs along the transect. A distinct gradient in chlorophyll a concentrations that increased from north (2.1 μg 1-1) to south (18.9 μg 1-1) indicated that the dominant blooms occurred from the southern Bothnian Sea to the Baltic proper. High fucoxanthin (3.9 μg 1-1) and peridinin (1.9 μg 1-1) concentrations in the Bothnian Bay and Sea reflected late stages of diatom and dinoflagellate blooms, respectively, that typically occur in summer months in the northern Baltic (Andersson et al. 1996). High zeaxanthin (8 μg 1-2) concentrations in the southern Bothnian Sea and Baltic proper indicated dominance of cyanobacterial blooms in these regions. Decreasing concentrations of total lignin-phenols (A) from north (0.22) to south (0.02) indicated that terrestrial inputs of organic carbon were associated with high freshwater inflow into the northern Baltic. Further examination of lignin-phenol ratios indicated that the dominant source of terrestrial material into the Baltic was from woody gymnosperms.