Hard fragments (crushed only by a hammer) of manganese deposits differing strongly in appearance from the regional ferromanganese crusts were sampled from depths of 3500–3200 m during the dredging of an unnamed seamount in the Central Basin of the Sea of Japan. Their surface has a black carbonaceous coating; after its removal, the crusts become steel-gray. The specific weight of these crust fragments is 3.35 g/cm3, whereas the regional crusts have a specific weight of <2 g/cm3. X-ray diffraction analysis showed that the sampled fragments consist of pure pyrolusite. There are also fragments of crusts formed by todorokite and birnessite. All pyrolusite samples have an abnormally high content of Mn (up to 63%). The Mn/Fe ratio reaches 9016. The conclusion is drawn that the manganese crusts formed on this seamount are of hydrothermal genesis.
<p>Continuous measurements of gaseous elemental mercury (Hg(0)) in the marine boundary layer (MBL) and Hg(0) fluxes were conducted in the Sea of Japan and the Sea of Okhotsk from September 7 to October 17, 2019. All Hg(0) measurements were carried out using two RA-915M mercury analysers (Lumex LLC, Russia). Hg(0) concentrations in the air were measured at two levels (about 2 m and 20 m above the sea surface) with a time resolution of 30 minutes. Hg(0) fluxes were measured at five sample stations using a dynamic flux chamber.</p><p>During the cruise Hg(0) concentrations varied in the range from 0,47 ng/m<sup>3</sup> to 1,55 ng/m<sup>3</sup>, and from 0,31 ng/m<sup>3</sup> to 2,71 ng/m<sup>3</sup> with medians of 0,92 ng/m<sup>3</sup> for 2 m and 20 m, respectively. Atmospheric Hg(0) concentrations in measurements sites were strongly depended on the regions from where air masses came to the study areas. As a result of the Concentration Weighted Trajectory (CWT) analysis we established 2 regions that influenced the Hg(0) concentrations during the cruise: the Northeast China with the Yellow Sea region and the Kurile Islands sector of the Pacific Ocean. The arrival of air masses from China and the Yellow Sea region caused an increase in Hg(0) concentrations in the air in the Sea of Japan and the Sea of Okhotsk. Elevated concentrations were also observed In the Sea of Okhotsk during the periods air masses came from the Kurile Islands sector of the Pacific Ocean.</p><p>Hg(0) fluxes were measured at 3 stations in the Sea of Japan and at 2 stations in the Sea of Okhotsk. The values ranged from 0,57 ng/m<sup>2</sup>/h to 1,55 ng/m<sup>2</sup>/h, with median value of 1,32 ng/m<sup>2</sup>/h. A positive relationships between Hg(0) flux and air and water temperature were observed.</p><p>This work was supported by the Russian Science Foundation (RSF) (Project &#8470; 19-77-10011) and by the National Natural Science Foundation of China (Projects &#8470;: 41876065, 41420104005, U1606401) and National Program on Global Change and Air-Sea Interaction (Project &#8470; GASI-GEOGE-04).</p>
Data are presented on the chemical composition and the content of microelements including REEs in samples of pyrolusite, todorokite, and birnessite collected from a depth of 3500-3200 m by dredging a nameless elevation in the Central Basin of the Sea of Japan. The samples of pyrolusite are characterized by high hardness and density (3.35 g/cm 3 ). The conclusion of their hydrothermal genesis is made.
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