The nature of ferromanganese concretions from the eastern gulf of Finland, Baltic Sea

Composition and genesis of ferromanganese deposits from the northern South China Sea

“…The nodules physical properties such as maximum diameter, density, and weight are similar to nodules reported to occur in the shallow-waters and continental margins in the Baltic Sea, the Gulf of Finland, Black Sea and the Gulf of Cadiz (e.g., Hlawatsch et al, 2002;González et al, 2007;Zhamoida et al, 2007;Baturin, 2010). Rodlike, irregular and concretion morphologies are predom-inant in the Province A nodules (Table 1) as in other shallow water nodules such as those reported from the Gulf of Cadiz (González et al, 2007).…”

“…10d). In addition, the average GR of the NESCS nodules (3320 mm/Myr) is slower than those calculated for shallow-water Baltic Sea nodules (average rate is 20,000 mm/ Myr) (Zhamoida et al, 1996;Hlawatsch et al, 2002), but several (Baturin et al, 2002), Gulf of Cadiz (González et al, 2009), East China Sea (Shan, 1984), Western Philippine Sea (He, 1991;Xu et al, 2006), California margin (Conrad et al, in press). Ocean basins: NW Pacific (Hein et al, 2012), Indian Ocean (Chandnani et al, 2012) and Clarion-Clipperton Fracture Zone (CCFZ) (Wegorzewski and Kuhn, 2014).…”

Extensive Coverage of Marine Mineral Concretions Revealed in Shallow Shelf Sea Areas

“…Previous studies have observed concretions mainly below 40 m depth on ridges and slopes above the depth zone of permanent mud and clay deposition, but less so near the coast in shallower waters (Boström et al, 1982). The major areas of ferromanganese concretions have been concluded to be found on the fringes of seafloor depressions (Glasby et al, 1997), with only scattered occurrences in shallower areas above 40 m depth (Zhamoida et al, 2007). While mineral concretions are known to exist in many parts of coastal sea areas, e.g., in the Black Sea (Baturin, 2010) north-east Atlantic Ocean (González et al, 2010), South China Sea (Zhong et al, 2017), and Kara Sea (Vereshchagin et al, 2019), and the processes affecting their formation have been intensively studied (Ingri, 1985b;Baturin, 2010;González et al, 2010), specific information on their abundance and spatial coverage is still lacking.…”

“…Concretion formation is further driven by microbial reduction, and the diverse bacterial communities associated with concretions affect both their growth and dissolution (Zhang et al, 2002;Yli-Hemminki et al, 2014). As a result of their complex formation mechanisms, the distribution and abundance of mineral concretions on the seafloor is heterogeneous, and they are found in variable shapes and sizes, ranging from < 2 mm buckshot concretions to crusts of >1 m. They are present in a variety of geological settings, and their growth rates vary, depending on environmental conditions, from 0.003 to 0.3 mm a −1 (Zhamoida et al, 2007;Grigoriev et al, 2013). Under oxygen rich conditions, iron and manganese tend to form oxides, contributing to the growth of concretions, while in anoxic conditions concretions are partly dissolved (Zhamoida et al, 2007;Yli-Hemminki et al, 2016).…”

“…Mineral precipitates form hard substrates on predominantly soft seafloors, and they are therefore suggested to increase habitat complexity (Vanreusel et al, 2016) and to provide shelter from seafloor erosion . Due to their capacity to absorb heavy metals and phosphorus, FeMn concretions may further be considered as natural filters on the seafloor (Hlawatsch et al, 2002) and they likely act as a buffering system between oxidized and reduced conditions (Zhamoida et al, 2007). Their ability to trap heavy metals and rare earth elements is related to the mineralogy of the concretions, with especially Mn oxides having a high sorption capacity for metal cations (Miyata et al, 2007).…”