Chemistry of suspended particles in the southern Baltic Sea

Abstract

Dissolved and suspended concentrations of Al, Ba, Fe, Mn, and Si and suspended P and Ti have been studied in the Baltic proper, the Belt Sea-Kattegat and the Åland Sea. Approximately 20% of total Al, Fe and Mn, 75% of total Si and 99% of total Ba passed a 0.45-μm filter in subsurface water from the Baltic proper. The suspended phase can be divided into three major components, a detrital, a Mn rich and an organic phase. Suspended Al, Ti and most Fe were present in detrital particles. Approximately 50% of suspended Si was detrital while the amount of P in the detrital component was negligible. Suspended P showed a positive correlation to the non-detrital Fe concentration. Non-detrital Mn was strongly enriched in the suspended phase. In some samples 50% of the ashed suspended load was Mn. The Mn-rich particles originate from seasonally anoxic waters within the Baltic proper. During an anoxic episode in the Landsort Deep high dissolved concentrations of Mn were built up in the oxygen-free zone. A concentration of 700 μg l −1 was measured in the bottom water. Dissolved Mn concentrations dropped to values below 1 μg l −1, when the whole water column was oxygenated. Mn-rich particles, 40–80 μg l −1 suspended Mn, were found in the former reduced zone. Large temporal variations in the dissolved and suspended Mn concentrations were observed in the oxidized water column during the studied period. Both Ba and P were scavenged by the Mn-rich phase.