Ferromanganese summer

In the summer of 2022, Geological Survey of Finland (GTK) has been busy collecting ferromanganese concretions on the research vessel Geomari from several sites along the Finnish south coast, from the Eastern Gulf of Finland to the Archipelago Sea. The concretions have been collected for the Fermaid project, funded by the Academy of Finland, and for the FeCoVERY project, funded by the Finnish Natural Resources Research Foundation.

Ferromanganese concretions are spheroidal, discoidal or plate-like precipitates of iron and manganese hydroxides (Figure 1). They grow slowly on the seafloor and at the same time sequester various substances from the seawater such as phosphorus, nickel, cobalt and rare earth elements.

The Fermaid project studies ferromanganese concretions as paleoceanographic records. Variations in the amounts and isotope ratios of trace elements sequestered in the concretion growth layers at different times reflect conditions in the seafloor environment, such as the oxygen levels and salinity. Ferromanganese concretions therefore record variability in the marine environment in a similar way to sediments deposited on the seafloor, but they are formed in areas where sediment is not being deposited, which makes studying them particularly interesting. The Fermaid project is a collaboration with the University of Helsinki, Tallinn University of Technology, Stockholm University, Australian National University in Canberra and Harvard University.

In the FeCoVERY project, ferromanganese concretions are grown in the laboratory and the effects of geochemical and microbiological processes on their growth are studied. The purpose is to find out experimentally how changes in environmental conditions exactly regulate the sequestration and isotopic composition of trace metals such as cobalt and nickel in ferromanganese concretions, and what is the role of microbial communities in the process. The FeCoVERY project is a collaboration with the University of Helsinki.

Joonas Virtasalo