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The redox-sensitive trace metal manganese (Mn) is an important electron donor and acceptor in aquatic environments. In stratified basins, the transformation between dissolved Mn2 +, 3 + and particulate Mn(III/IV) oxides constitutes the “manganese pump” at the redoxcline, which separates the oxic surface from anoxic bottom waters. In addition to fluxes of dissolved components and reaction rates, accurate estimates of the sinking velocities of authigenic Mn oxides (MnOx) are an important prerequisite to balance and model such euxinic systems. However, models describing biogeochemical cycles suffer from the lack of measured particle sinking velocities and instead must rely on values calculated according to Stokes' law or on estimates derived from budget calculations. Here we present the first stationary sinking velocities of authigenic MnOx particles from the pelagic redoxclines of the currently anoxic Landsort and Gotland Deeps (Baltic Sea). Sinking velocities were determined on board ship by using high-resolution backlit imaging (shadowgraphy) and manual particle tracking. Within the typical size range of MnOx particles (2–20 μm), the average sinking velocity of 1972 particles was determined to be 0.76 m d− 1, distinctly lower than the values calculated according to Stokes' law and those used in various models. This difference could be attributed to the observed star-shaped structure of the MnOx particles, which was far away from a spherical shape, and to the embedment of the particles in a complex organic matrix, which significantly modified their density and consequently their sinking velocity.

Continuous flow analysis for soluble Fe(II) species in seawater was performed with a colorimetric method using ferene as a spectrophotometric reagent. The method is based on the measurement of absorbance of the [FeII(fer)3]4 --complex at 594 nm. No preconcentration-steps are required. Samples prepared in the laboratory in line with external calibration experiments have been successfully analyzed in the nanomolar range (R2 = 0.959). A detection limit of 20 nM was obtained. Furthermore, investigations were performed in situ with a wet chemical analyzer in the water column of the central Baltic Sea. Finally the results were consistent with measurements made by an independent laboratory based method (ICP-OES).

In autumn 2002 a time-series station was installed in the tidal inlet between the Islands of Langeoog and Spiekeroog (Southern North Sea, NW Germany) to continuously measure physical, chemical, and meteorological parameters, even during extreme weather conditions (gale-force storms, drifting ice). Inside the pole of the station sensor tubes are installed in direction of the prevailing tidal currents. The tubes are equipped with hydrographic sensors (pressure, temperature, conductivity) and allow retrieval of water for nutrient analysis by automated instruments located inside the pole. Dissolved methane and the nutrients ammonia, nitrite, nitrate, phosphate, and silicate are measured at the station. Nutrient patterns obtained during spring and summer 2006 reflect the development of nutrient concentrations during the annual spring phytoplankton bloom. Methane measurements showed a tidal dependence with maxima at low tide, which emphasizes the tidal flat sediments as the dominating source for methane in the open coastal water column.