Slow-sinking particle export measured in the North Atlantic during the M87/1 cruise in April 2012

Slow-sinking particles were sampled using the Marine Snow Catcher (MSC). For a full description of the MSC and flux calculations see Riley et al. (2012). The MSC was deployed at four depths between 50 - 650 m during four visit at Stations 1 (63°3' N 11°0' W) and three visits at Station 2 (62°5' N 2°3' W) to obtain depth profiles of slow-sinking material. The MSC was further deployed at 50 m during two visits at Station 3 (60°2' N 1°0' E). A total of 33 MSC were deployed. Slow-sinking particles were analysed for particulate organic carbon (POC), particulate inorganic carbon (PIC), biogenic silica (BSi), and Chlorophyll a (total, >10 µm).

(Table 1) Composition of manganese-iron accumulates in the Kiel Bay, western Baltic Sea

Manganese-iron accumulates in the Kiel Bay were investigated with regard to their occurence, chemical composition and formation. Three morphologically different types were identified: a) growth on mussels, b) spherical nodules (ca. 1-3 cm) and c) disshaped symetrical and asymetrical nodules (up to 10 cm). Average values from 110 accumulates representing the three types were: Mn 29.3%, Fe 10.0%, Co 77 ppm, Ni 97 ppm, Cu 21 ppm and Zn 340 ppm. Accumulates on mussels showed the highest trace metal concentrations. A growth rate of ca. 0.6 mm/yr for type (a) was estimated. Heavy metal concentrations were determined in ca. 60 sediment and 30 pore water samples, and in 110 Baltic sea water samples. During certain periods, large increases in Mn values (up to 400 (µg/l) were found in the deeper waters. These concentrations develop during periods of strong stagnant conditions in the sediments where dissolution of Mn oxides, and diffusion mobilizes the Mn into the overlying waters. The manganese is then reprecipitated close to the boundary of the O2-enriched surface waters. This critical O2-concentration was found to be 40% saturation. In the Kiel Bay, Mn-Fe-accumulates are found in a zone which marks the upper limit sometimes reached by the deep waters of lower O2-concentration. Additionally, the availability of larger particles (especially stones or mussels) on the sediment surface is necessary. These conditions are met in the Kiel Bay in a water depth of 20-28 m at several places.